TY - BOOK TI - World Scientific handbook of organic optoelectronic devices A3 - So, Franky A3 - Huang, Jinsong A3 - Yongbo, Yuan A3 - Thompson, Barry C. DA - 2018/// PY - 2018/// PB - World Scientific Publishing Company ER - TY - JOUR TI - Soft X-ray Microscopy: History, Status, and Future AU - Ade, Harald T2 - Microscopy and Microanalysis AB - An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button. DA - 2018/8// PY - 2018/8// DO - 10.1017/S1431927618005494 VL - 24 IS - S1 SP - 1000-1001 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927618005494 DB - Crossref ER - TY - JOUR TI - Long-Lived, Non-Geminate, Radiative Recombination of Photogenerated Charges in a Polymer/Small-Molecule Acceptor Photovoltaic Blend AU - Ziffer, Mark E. AU - Jo, Sae Byeok AU - Zhong, Hongliang AU - Ye, Long AU - Liu, Hongbin AU - Lin, Francis AU - Zhang, Jie AU - Li, Xiaosong AU - Ade, Harald W. AU - Jen, Alex K.-Y. AU - Ginger, David S. T2 - Journal of the American Chemical Society AB - Minimization of open-circuit-voltage ( VOC) loss is required to transcend the efficiency limitations on the performance of organic photovoltaics (OPV). We study charge recombination in an OPV blend comprising a polymer donor with a small molecule nonfullerene acceptor that exhibits both high photovoltaic internal quantum efficiency and relatively high external electroluminescence quantum efficiency. Notably, this donor/acceptor blend, consisting of the donor polymer commonly referred to as PCE10 with a pseudoplanar small molecule acceptor (referred to as FIDTT-2PDI) exhibits relatively bright delayed photoluminescence on the microsecond time scale beyond that observed in the neat material. We study the photoluminescence decay kinetics of the blend in detail and conclude that this long-lived photoluminescence arises from radiative nongeminate recombination of charge carriers, which we propose occurs via a donor/acceptor CT state located close in energy to the singlet state of the polymer donor. Additionally, crystallographic and spectroscopic studies point toward low subgap disorder, which could be beneficial for low radiative and nonradiative losses. These results provide an important demonstration of photoluminescence due to nongeminate charge recombination in an efficient OPV blend, a key step in identifying new OPV materials and materials-screening criteria if OPV is to approach the theoretical limits to efficiency. DA - 2018/7/14/ PY - 2018/7/14/ DO - 10.1021/JACS.8B05834 VL - 140 IS - 31 SP - 9996-10008 J2 - J. Am. Chem. Soc. LA - en OP - SN - 0002-7863 1520-5126 UR - http://dx.doi.org/10.1021/JACS.8B05834 DB - Crossref ER - TY - JOUR TI - Controlling Blend Morphology for Ultrahigh Current Density in Nonfullerene Acceptor-Based Organic Solar Cells AU - Song, Xin AU - Gasparini, Nicola AU - Ye, Long AU - Yao, Huifeng AU - Hou, Jianhui AU - Ade, Harald AU - Baran, Derya T2 - ACS Energy Letters AB - In this Letter, we highlight a system with a well-known polymer donor (PTB7-Th) blended with a narrow band gap nonfullerene acceptor (IEICO-4F) as the active layer and 1-chloronaphthalene (CN) as the solvent additive. Optimization of the photoactive layer nanomorphology yields a short-circuit current density value of 27.3 mA/cm2, one of the highest values in organic solar cells reported to date, which competes with other types of solution-processed solar cells such as perovskite or quantum dot devices. Along with decent open-circuit voltage (0.71 V) and fill factor values (66%), a power conversion efficiency of 12.8% is achieved for the champion devices. Morphology characterizations elucidate that the origin of this high photocurrent is mainly the increased π–π coherence length of the acceptor, the domain spacing, as well as the mean-square composition variation of the blend. Optoelectronic measurements confirm a balanced hole and electron mobility and reduced trap-assisted recombination for the best devices. DA - 2018/1/23/ PY - 2018/1/23/ DO - 10.1021/ACSENERGYLETT.7B01266 VL - 3 IS - 3 SP - 669-676 J2 - ACS Energy Lett. LA - en OP - SN - 2380-8195 2380-8195 UR - http://dx.doi.org/10.1021/ACSENERGYLETT.7B01266 DB - Crossref ER - TY - JOUR TI - Polymer Solar Cells: Miscibility-Function Relations in Organic Solar Cells: Significance of Optimal Miscibility in Relation to Percolation (Adv. Energy Mater. 28/2018) AU - Ye, Long AU - Collins, Brian A. AU - Jiao, Xuechen AU - Zhao, Jingbo AU - Yan, He AU - Ade, Harald T2 - Advanced Energy Materials AB - In article number 1703058, Harald Ade and co-workers present the determination of liquidus miscibility and its temperature dependence of organic films by scanning transmission X-ray microscopy and outline an approach to convert liquidus miscibility to an effective Flory-Huggins interaction parameter χ, which will pave a way to predict morphology and processing strategies of polymer solar cells. DA - 2018/10// PY - 2018/10// DO - 10.1002/AENM.201870124 VL - 8 IS - 28 SP - 1870124 J2 - Adv. Energy Mater. LA - en OP - SN - 1614-6832 UR - http://dx.doi.org/10.1002/AENM.201870124 DB - Crossref ER - TY - JOUR TI - Surpassing 10% Efficiency Benchmark for Nonfullerene Organic Solar Cells by Scalable Coating in Air from Single Nonhalogenated Solvent AU - Ye, Long AU - Xiong, Yuan AU - Zhang, Qianqian AU - Li, Sunsun AU - Wang, Cheng AU - Jiang, Zhang AU - Hou, Jianhui AU - You, Wei AU - Ade, Harald T2 - Advanced Materials AB - The commercialization of nonfullerene organic solar cells (OSCs) critically relies on the response under typical operating conditions (for instance, temperature and humidity) and the ability of scale-up. Despite the rapid increase in power conversion efficiency (PCE) of spin-coated devices fabricated in a protective atmosphere, the efficiencies of printed nonfullerene OSC devices by blade coating are still lower than 6%. This slow progress significantly limits the practical printing of high-performance nonfullerene OSCs. Here, a new and relatively stable nonfullerene combination is introduced by pairing the nonfluorinated acceptor IT-M with the polymeric donor FTAZ. Over 12% efficiency can be achieved in spin-coated FTAZ:IT-M devices using a single halogen-free solvent. More importantly, chlorine-free, blade coating of FTAZ:IT-M in air is able to yield a PCE of nearly 11% despite a humidity of ≈50%. X-ray scattering results reveal that large π-π coherence length, high degree of face-on orientation with respect to the substrate, and small domain spacing of ≈20 nm are closely correlated with such high device performance. The material system and approach yield the highest reported performance for nonfullerene OSC devices by a coating technique approximating scalable fabrication methods and hold great promise for the development of low-cost, low-toxicity, and high-efficiency OSCs by high-throughput production. DA - 2018/1/10/ PY - 2018/1/10/ DO - 10.1002/ADMA.201705485 VL - 30 IS - 8 SP - 1705485 J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/ADMA.201705485 DB - Crossref KW - blade coating KW - film morphology KW - nonfullerene acceptors KW - nonhalogenated solvents KW - organic solar cells ER - TY - JOUR TI - Enhanced piezoelectricity of thin film hafnia-zirconia (HZO) by inorganic flexible substrates AU - Hsain, H. Alex AU - Sharma, Pankaj AU - Yu, Hyeonggeun AU - Jones, Jacob L. AU - So, Franky AU - Seidel, Jan T2 - Applied Physics Letters AB - Hf0.5Zr0.5O2 (HZO) films are grown on rigid glass and flexible polyimide substrates using non-rapid thermal annealing. Films are comparatively investigated using macroscopic and local probe-based approaches to characterize their ferroelectric and piezoelectric properties. The polarization-electric field (P-E) measurements reveal that the ferroelectric characteristics of these thin films agree with the observed switchable piezoresponse hysteresis loops as well as electrically written, oppositely oriented domains. Moreover, the HZO thin films grown on flexible polyimide substrates display significantly enhanced piezoelectric response in comparison to the films grown on rigid substrates. This effect is likely due to improved domain wall motion caused by the mechanical release of the film-substrate couple. These findings suggest that inherently lead-free HZO thin films on flexible substrates are potential candidate materials for improved piezoelectric applications in wearable devices. DA - 2018/7/9/ PY - 2018/7/9/ DO - 10.1063/1.5031134 VL - 113 IS - 2 SP - 022905 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.5031134 DB - Crossref ER - TY - JOUR TI - Semi-transparent vertical organic light-emitting transistors AU - Yu, Hyeonggeun AU - Ho, Szuheng AU - Barange, Nilesh AU - Larrabee, Ryan AU - So, Franky T2 - Organic Electronics AB - Vertical organic light-emitting transistor (VOLET) having an organic light-emitting diode integrated with a vertical thin-film transistor is promising for transparent electronics because the vertical device structure potentially offers a display with a large aperture ratio and a low power consumption. However, making a transparent VOLET has been challenging due to the requirements for all transparent electrodes including fabrication of a porous source electrode for current modulation in the device. Here, we report a semi-transparent VOLET with a large modulation of light emitted through the top and bottom electrodes using a nano-porous indium-tin oxide (ITO) source electrode, a Mg:Ag drain electrode, and an ITO gate electrode. The porous ITO source electrode is not only important for luminance modulation, but the nano-textured film morphology also enhances light extraction from the device. Finally, we show that the off current of the VOLET can be suppressed with an electron transporting layer (C60), leading to a large luminance on/off ratio of 104. DA - 2018/4// PY - 2018/4// DO - 10.1016/J.ORGEL.2018.01.030 VL - 55 SP - 126-132 J2 - Organic Electronics LA - en OP - SN - 1566-1199 UR - http://dx.doi.org/10.1016/J.ORGEL.2018.01.030 DB - Crossref KW - Vertical field effect transistor KW - Light-emitting transistor KW - Light extraction KW - Transparent electronic KW - Porous electrode ER - TY - JOUR TI - Vertical Organic-Inorganic Hybrid Perovskite Schottky Junction Transistors AU - Yu, Hyeonggeun AU - Cheng, Yuanhang AU - Shin, Donghun AU - Tsang, Sai-Wing AU - So, Franky T2 - Advanced Electronic Materials AB - Abstract While organolead halide perovskite materials have attracted considerable attention for high efficiency solar cells, they have shown little potential for use in field‐effect transistors (FETs) due to the limited current modulation at room temperature. Here, by developing a vertically gated methylammonium lead iodide (MAPbI 3 )/indium‐tin oxide (ITO) Schottky junction, a room temperature‐operable vertical MAPbI 3 thin‐film transistor is reported. Due to the injection‐controlled gating mechanism as well as the vertical channel structure, a current modulation ratio up to 10 4 is achieved. Fabrication of a nanoporous ITO source electrode forming a highly rectifying Schottky junction with the MAPbI 3 layer is the key for the large current modulation. It is discovered that the electron transporting layers on top of the MAPbI 3 layer play an important role in achieving a large current rectification of 10 7 at the Schottky junction and hence large current on/off ratios of the resulting transistor. DA - 2018/3/22/ PY - 2018/3/22/ DO - 10.1002/AELM.201800039 VL - 4 IS - 5 SP - 1800039 J2 - Adv. Electron. Mater. LA - en OP - SN - 2199-160X UR - http://dx.doi.org/10.1002/AELM.201800039 DB - Crossref KW - organic-inorganic hybrid perovskite KW - patterned electrodes KW - Schottky junctions KW - vertical transistors ER - TY - JOUR TI - Impact of Nonfullerene Molecular Architecture on Charge Generation, Transport, and Morphology in PTB7-Th-Based Organic Solar Cells AU - Yi, Xueping AU - Gautam, Bhoj AU - Constantinou, Iordania AU - Cheng, Yuanhang AU - Peng, Zhengxing AU - Klump, Erik AU - Ba, Xiaochu AU - Ho, Carr Hoi Yi AU - Dong, Chen AU - Marder, Seth R. AU - Reynolds, John R. AU - Tsang, Sai-Wing AU - Ade, Harald AU - So, Franky T2 - Advanced Functional Materials AB - Abstract Despite the rapid development of nonfullerene acceptors (NFAs), the fundamental understanding on the relationship between NFA molecular architecture, morphology, and device performance is still lacking. Herein, poly[[4,8‐bis[5‐(2‐ethylhexyl)thiophene‐2‐yl]benzo[1,2‐b:4,5‐b0]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]] (PTB7‐Th) is used as the donor polymer to compare an NFA with a 3D architecture (SF‐PDI4) to a well‐studied NFA with a linear acceptor–donor–acceptor (A–D–A) architecture (ITIC). The data suggest that the NFA ITIC with a linear molecular structure shows a better device performance due to an increase in short‐circuit current ( J sc ) and fill factor (FF) compared to the 3D SF‐PDI4. The charge generation dynamics measured by femtosecond transient absorption spectroscopy (TAS) reveals that the exciton dissociation process in the PTB7‐Th:ITIC films is highly efficient. In addition, the PTB7‐Th:ITIC blend shows a higher electron mobility and lower energetic disorder compared to the PTB7‐Th:SF‐PDI4 blend, leading to higher values of J sc and FF. The compositional sensitive resonant soft X‐ray scattering (R‐SoXS) results indicate that ITIC molecules form more pure domains with reduced domain spacing, resulting in more efficient charge transport compared with the SF‐PDI4 blend. It is proposed that both the molecular structure and the corresponding morphology of ITIC play a vital role for the good solar cell device performance. DA - 2018/6/21/ PY - 2018/6/21/ DO - 10.1002/ADFM.201802702 VL - 28 IS - 32 SP - 1802702 J2 - Adv. Funct. Mater. LA - en OP - SN - 1616-301X UR - http://dx.doi.org/10.1002/ADFM.201802702 DB - Crossref KW - charge generation KW - charge transport KW - molecular architecture KW - morphology KW - nonfullerene acceptors ER - TY - JOUR TI - Increased Exciton Delocalization of Polymer upon Blending with Fullerene AU - Gautam, Bhoj AU - Klump, Erik AU - Yi, Xueping AU - Constantinou, Iordania AU - Shewmon, Nathan AU - Salehi, Amin AU - Lo, Chi Kin AU - Zheng, Zilong AU - Brédas, Jean-Luc AU - Gundogdu, Kenan AU - Reynolds, John R. AU - So, Franky T2 - Advanced Materials AB - Abstract Interfaces between donor and acceptor in a polymer solar cell play a crucial role in exciton dissociation and charge photogeneration. While the importance of charge transfer (CT) excitons for free carrier generation is intensively studied, the effect of blending on the nature of the polymer excitons in relation to the blend nanomorphology remains largely unexplored. In this work, electroabsorption (EA) spectroscopy is used to study the excited‐state polarizability of polymer excitons in several polymer:fullerene blend systems, and it is found that excited‐state polarizability of polymer excitons in the blends is a strong function of blend nanomorphology. The increase in excited‐state polarizability with decreased domain size indicates that intermixing of states at the interface between the donor polymers and fullerene increases the exciton delocalization, resulting in an increase in exciton dissociation efficiency. This conclusion is further supported by transient absorption spectroscopy and time‐resolved photoluminescence measurements, along with the results from time‐dependent density functional theory calculations. These findings indicate that polymer excited‐state polarizability is a key parameter for efficient free carrier generation and should be considered in the design and development of high‐performance polymer solar cells. DA - 2018/6/11/ PY - 2018/6/11/ DO - 10.1002/adma.201801392 VL - 30 IS - 30 SP - 1801392 J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/adma.201801392 DB - Crossref KW - charge transfer states KW - electroabsorption KW - exciton delocalization KW - Frenkel exciton KW - polarizability ER - TY - JOUR TI - Randomly Distributed Conjugated Polymer Repeat Units for High-Efficiency Photovoltaic Materials with Enhanced Solubility and Processability AU - Xu, Bing AU - Pelse, Ian AU - Agarkar, Shruti AU - Ito, Shunichiro AU - Zhang, Junxiang AU - Yi, Xueping AU - Chujo, Yoshiki AU - Marder, Seth AU - So, Franky AU - Reynolds, John R. AU - al. T2 - ACS APPLIED MATERIALS & INTERFACES AB - Three structurally disordered terpolymer derivatives of PffBT4T-2OD (PCE11), prepared by replacing a varied amount of bithiophene linkers with single thiophenes, were found to exhibit reduced aggregation in solution with increasing thiophene content, while important redox and optoelectronic properties remained similar to those of PffBT4T-2OD. Solar cells based on random terpolymer-PC71BM blends exhibited average power conversion efficiencies of over 9.5% when processed with preheated substrates, with fill factors above 70%, exceeding those from PffBT4T-2OD. Thanks to increased solubility, random terpolymer devices were able to be fabricated on room-temperature substrates, reaching virtually identical performance among all three polymers despite remarkable thicknesses of ∼400 nm. Thus, we show that the random terpolymer approach is successful in improving processability while maintaining device performance. DA - 2018/12/26/ PY - 2018/12/26/ DO - 10.1021/acsami.8b15522 VL - 10 IS - 51 SP - 44583-44588 SN - 1944-8244 KW - conjugated polymers KW - organic photovoltaics KW - random terpolymers KW - bulk heterojunction solar cells KW - organic electronics ER - TY - JOUR TI - Donor polymer based on alkylthiophene side chains for efficient non- fullerene organic solar cells: insights into fluorination and side chain effects on polymer aggregation and blend morphology AU - Liu, Jing AU - Ma, Lik-Kuen AU - Li, Zhengke AU - Hu, Huawei AU - Sheong, Fu Kit AU - Zhang, Guangye AU - Ade, Harald AU - Yan, He T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - The synergistic effects of overfluorination and alkylthiophene side chain strategies led to 10.60% efficiency for non-fullerene organic solar cells. DA - 2018/12/14/ PY - 2018/12/14/ DO - 10.1039/c8ta08769e VL - 6 IS - 46 SP - 23270-23277 SN - 2050-7496 ER - TY - JOUR TI - Side-Chain Sequence Enabled Regioisomeric Acceptors for Conjugated Polymers AU - Luo, Xuyi AU - Tran, Dung T. AU - Kadlubowski, Natalie M. AU - Ho, Carr Hoi Yi AU - Riley, Parand AU - So, Franky AU - Mei, Jianguo T2 - MACROMOLECULES AB - Side-chain sequence enabled regioisomeric acceptors, bearing different side-chain sequences on the same conjugated backbone, are herein reported. Two regioregular polymers PTBI-1 and PTBI-2 and one regiorandom polymer PTBI-3 were synthesized from these two regioisomeric acceptors for a comparative study. UV–vis–NIR absorption spectroscopy and electrochemical study confirmed similar frontier molecular orbital levels of the three polymers in their solid state. More intriguingly, absorption profiles suggest that the sequence of side chains greatly governs the aggregation behaviors. Furthermore, the PTBI-2 film shows larger ordered domains than PTBI-1 and PTBI-3 films, as supported by AFM and GIWAXS measurements. As a result, PTBI-2-based FET devices achieved an average hole mobility of 1.37 cm2 V–1 s–1, much higher than the two polymers with other side-chain sequences. The regiorandom PTBI-3 exhibited the lowest average hole mobility of 0.27 cm2 V–1 s–1. This study highlights the significant impact of side-chain sequence regioisomerism on aggregation behaviors, morphologies, and subsequently charge transport properties of donor–acceptor type conjugated polymers. DA - 2018/11/13/ PY - 2018/11/13/ DO - 10.1021/acs.macromol.8b01946 VL - 51 IS - 21 SP - 8486-8492 SN - 1520-5835 ER - TY - JOUR TI - Donor Conjugated Polymers with Polar Side Chain Groups: The Role of Dielectric Constant and Energetic Disorder on Photovoltaic Performance AU - Xu, B. AU - Yi, X. AU - Huang, T. AU - Zheng, Z. AU - Zhang, J. AU - Salehi, A. AU - Coropceanu, V. AU - Ho, C.H.Y. AU - Marder, S.R. AU - Toney, M.F. AU - Brédas, J.-L. AU - So, F. AU - Reynolds, J.R. T2 - Advanced Functional Materials AB - Abstract To better understand the correlation of the dielectric properties with the photovoltaic response in conjugated polymer:fullerene bulk heterojunction materials, the concept of introducing minimal structural change is employed to increase the polymer dielectric constant via polar cyano groups added to the end of butyl or octyl side chains in the poly(dithienosilole‐thienopyrrolodione) system. Density functional theory calculations confirm that the polar groups do not affect the polymer electronic structure but can lead to an increase in overall dipole moment depending on the polymer chain conformation. Despite the increased dielectric constant (from 2.7 to 4.3 for cyano‐octyl side chains and from 2.7 to 3.2 for the cyano‐butyl analogues), the device characteristics employing the cyano‐containing polymers are inferior to those of the devices made with unfunctionalized alkyl chains. It is found that the hole mobilities for the cyano‐containing polymers are two orders of magnitude lower compared to those for the parent polymers and suggest this is due to an increase in energetic disorder caused by the strong local permanent dipoles associated with the cyano groups. The study highlights the complexity in the relationship between the dielectric constant of organic materials, the morphologies that are induced, and their photovoltaic performance. DA - 2018/// PY - 2018/// DO - 10.1002/adfm.201803418 VL - 28 IS - 46 SP - 1803418 SN - 1616-3028 KW - conjugated polymers KW - energetic disorder KW - organic electronics KW - organic solar cells KW - photovoltaic devices ER - TY - JOUR TI - A time-resolved millimeter wave conductivity (TR-mmWC) apparatus for charge dynamical properties of semiconductors AU - Roy, Biswadev AU - Jones, Charles R. AU - Vlahovic, B. AU - Ade, Harald W. AU - Wu, Marvin H. T2 - REVIEW OF SCIENTIFIC INSTRUMENTS AB - This article demonstrates a contactless, time-resolved, millimeter wave conductivity apparatus capable of measuring photoconductivity of a diverse range of materials. This cavity-less system determines the time-dependent magnitude of a sample’s charge carrier density-mobility product by monitoring the response of a continuous, millimeter-wave probe beam following excitation of the sample by an ultrafast laser pulse. The probe beam is tunable from 110 GHz to 170 GHz and the sample response data can be obtained over the sub-nanosecond to millisecond time interval. This system has been tested on silicon wafers, S-I GaAs, perovskite thin films, SiO2-Ge(nc), and CdSxSe1−x nanowire samples. We demonstrate a minimum detectable photoconductance change of ∼1 µS, an estimated time resolution for conductance decay of ∼100 ps, and a dynamic range greater than 57 dB. The calibration constant of the system, needed for quantitative calculation of photoconductivity from experimental data, has been determined using silicon wafers. This system has several advantages over currently used microwave and terahertz techniques, such as facile tunability of probe frequency and substantially wider time range for study of decay kinetics, while maintaining an open sample environment that enables characterization of a wide range of sample sizes under controlled environmental conditions. DA - 2018/10// PY - 2018/10// DO - 10.1063/1.5026848 VL - 89 IS - 10 SP - SN - 1089-7623 UR - https://doi.org/10.1063/1.5026848 ER - TY - JOUR TI - The finale of a trilogy: comparing terpolymers and ternary blends with structurally similar backbones for use in organic bulk heterojunction solar cells AU - Kelly, Mary Allison AU - Zhang, Qianqian AU - Peng, Zhengxing AU - Noman, Victoria AU - Zhu, Chenhui AU - Ade, Harald AU - You, Wei T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - Comparing the efficiency of terpolymers vs. ternary blends, this study focuses on two polymers with structurally similar backbones (monoCNTAZ and FTAZ) yet markedly different open circuit voltages. DA - 2018/10/21/ PY - 2018/10/21/ DO - 10.1039/c8ta05132a VL - 6 IS - 39 SP - 19190-19200 SN - 2050-7496 ER - TY - JOUR TI - Improvement of Photovoltaic Performance of Polymer Solar Cells by Rational Molecular Optimization of Organic Molecule Acceptors AU - Li, Xiaojun AU - Yao, Jia AU - Angunawela, Indunil AU - Sun, Chenkai AU - Xue, Lingwei AU - Liebman-Pelaez, Alexander AU - Zhu, Chenhui AU - Yang, Chunhe AU - Zhang, Zhi-Guo AU - Ade, Harald AU - Li, Yongfang T2 - ADVANCED ENERGY MATERIALS AB - Abstract Two n‐type organic semiconductor (n‐OS) small molecules m ‐ITIC‐2F and m ‐ITIC‐4F with fluorinated 2‐(2,3‐dihydro‐3‐oxo‐1H‐inden‐1‐ylidene)propanedinitrile (IC) terminal moieties are prepared, for the application as an acceptor in polymer solar cells (PSCs), to further improve the photovoltaic performance of the n‐OS acceptor 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene) indanone) ‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐sindaceno[1,2‐b:5,6‐b′]‐dithiophene ( m ‐ITIC). Compared to m ‐ITIC, these two new acceptors show redshifted absorption, higher molecular packing order, and improved electron mobilities. The power conversion efficiencies (PCE) of the as‐cast PSCs with m ‐ITIC‐2F or m ‐ITIC‐4F as an acceptor and a low‐cost donor–acceptor (D–A) copolymer PTQ10 as a donor reach 11.57% and 11.64%, respectively, which are among the highest efficiency for the as‐cast PSCs so far. Furthermore, after thermal annealing treatment, improved molecular packing and enhanced phase separation are observed, and the higher PCE of 12.53% is achieved for both PSCs based on the two acceptors. The respective and unique advantage with the intrinsic high degree of order, molecular packing, and electron mobilities of these two acceptors will be suitable to match with different p‐type organic semiconductor donors for higher PCE values, which provide a great potential for the PSCs commercialization in the near future. These results indicate that rational molecular structure optimization is of great importance to further improve photovoltaic properties of the photovoltaic materials. DA - 2018/8/16/ PY - 2018/8/16/ DO - 10.1002/aenm.201800815 VL - 8 IS - 23 SP - SN - 1614-6840 KW - molecular structure optimization KW - n-type organic semiconductors KW - organic molecule acceptors KW - polymer solar cells KW - power conversion efficiencies ER - TY - JOUR TI - Effects of fused-ring regiochemistry on the properties and photovoltaic performance of n-type organic semiconductor acceptors AU - Li, Xiaojun AU - Huang, He AU - Peng, Zhengxing AU - Sun, Chenkai AU - Yang, Dengchen AU - Zhou, Jiadong AU - Liebman-Pelaez, Alex AU - Zhu, Chenhui AU - Zhang, Zhi-Guo AU - Zhang, Zhanjun AU - Xie, Zengqi AU - Ade, Harald AU - Li, Yongfang T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - The effects of fused-ring regiochemistry on the physicochemical and photovoltaic properties of n-type organic semiconductor (n-OS) acceptors are investigated. DA - 2018/9/7/ PY - 2018/9/7/ DO - 10.1039/c8ta05920a VL - 6 IS - 33 SP - 15933-15941 SN - 2050-7496 ER - TY - JOUR TI - Effect of Side-Chain Engineering of Bithienylbenzodithiophene-alt-fluorobenzotriazole-Based Copolymers on the Thermal Stability and Photovoltaic Performance of Polymer Solar Cells AU - Huang, He AU - Bin, Haijun AU - Peng, Zhengxing AU - Qiu, Beibei AU - Sun, Chenkai AU - Liebman-Pelaez, Alex AU - Zhang, Zhi-Guo AU - Zhu, Chenhui AU - Ade, Harald AU - Zhang, Zhanjun AU - Li, Yongfang T2 - MACROMOLECULES AB - Side-chain engineering of conjugated polymer donor materials is an important way for improving photovoltaic performances of polymer solar cells (PSCs). On the basis of the polymer J61 synthesized in our group, here, we design and synthesize three new 2D-conjugated polymers J62, J63, and J64 with different types of side chains to further investigate the effect of side chain on their physicochemical and photovoltaic properties. With the narrow bandgap n-type organic semiconductor (n-OS) ITIC as acceptor, the optimized PSCs based on polymer donor of J62 with linear octyl, J63 with linear unsaturated hexylene, and J64 with cyclohexane side chains display power conversion efficiency (PCE) of 10.81%, 8.13%, and 8.59%, respectively. After thermal treatment at 200 °C for 2 h on the active layer,the PCE of the PSC based on J63 still keeps 92% of the original value, which verifies that the cross-linking of the polymer can improve the thermal stability of PSCs. Morphological studies show that the active layer based on J63 displays strong lamellar packing with RMS 1.26, and the active layer based on J64 shows little phase separation with RMS 0.65. The RMS of the active layer based on J62 is 0.900, and the size of phase separation is between that of J63 and J64, which indicates the excessive high lamellar packing or low phase separation is harmful to the performance of PSCs. These results indicate that the side-chain engineering is an effective way to adjust the aggregation of polymers and the morphology of blend films, which are key factors to influence the performance of PSCs. DA - 2018/8/14/ PY - 2018/8/14/ DO - 10.1021/acs.macromol.8b01036 VL - 51 IS - 15 SP - 6028-6036 SN - 1520-5835 ER - TY - JOUR TI - A Highly Crystalline Fused-Ring n-Type Small Molecule for Non-Fullerene Acceptor Based Organic Solar Cells and Field-Effect Transistors AU - Song, Xin AU - Gasparini, Nicola AU - Nahid, Masrur Morshed AU - Chen, Hu AU - Macphee, Sky Marie AU - Zhang, Weimin AU - Norman, Victoria AU - Zhu, Chenhui AU - Bryant, Daniel AU - Ade, Harald AU - McCulloch, Iain AU - Baran, Derya T2 - ADVANCED FUNCTIONAL MATERIALS AB - Abstract N‐type organic small molecules (SMs) are attracting attention in the organic electronics field, due to their easy purification procedures with high yield. However, only a few reports show SMs that perform well in both organic field‐effect transistors (OFETs) and organic solar cells (OSCs). Here, the synthesis and characterization of an n‐type small molecule with an indacenodithieno[3,2‐b]thiophene (IDTT) core unit and linear alkylated side chain (C 16 ) (IDTTIC) are reported. Compared to the state‐of‐the‐art n‐type molecule IDTIC, IDTTIC exhibits smaller optical bandgap and higher absorption coefficient, which is due to the enhanced intramolecular effect. After mixing with the polymer donor PBDB‐T, IDTIC‐based solar cells deliver a power conversion efficiency of only 5.67%. In stark contrast, the OSC performance of IDTTIC improves significantly to 11.2%. It is found that the superior photovoltaic properties of PBDB‐T:IDTTIC blends are mainly due to reduced trap‐assisted recombination and enhanced molecular packing coherence length and higher domain purity when compared to IDTIC. Moreover, a significantly higher electron mobility of 0.50 cm 2 V −1 s −1 for IDTTIC in OFET devices than for IDTIC (0.15 cm 2 V −1 s −1 ) is obtained. These superior performances in OSCs and OFETs demonstrate that SMs with extended π‐conjugation of the backbone possess a great potential for application in organic electronic devices. DA - 2018/8/29/ PY - 2018/8/29/ DO - 10.1002/adfm.201802895 VL - 28 IS - 35 SP - SN - 1616-3028 KW - fused-ring small molecules KW - high photo-to-current efficiency KW - non-fullerene acceptors KW - organic field-effect transistors KW - organic solar cells ER - TY - JOUR TI - Miscibility-Function Relations in Organic Solar Cells: Significance of Optimal Miscibility in Relation to Percolation AU - Ye, Long AU - Collins, Brian A. AU - Jiao, Xuechen AU - Zhao, Jingbo AU - Yan, He AU - Ade, Harald T2 - ADVANCED ENERGY MATERIALS AB - Abstract Polymer solar cells (PSCs) continue to be a promising low‐cost and lead‐free photovoltaic technology. Of critical importance to PSCs is understanding and manipulating the composition of the amorphous mixed phase, which is governed by the thermodynamic molecular interactions of the polymer donor and acceptor molecules and the kinetics of the casting process. This progress report clarifies and defines nomenclature relating to miscibility and its relevance and implications to PSC devices in light of new developments. Utilizing a scanning transmission X‐ray microscopy method, the temperature dependences of “molecular miscibility” in the presence of fullerene crystals, now referred to liquidus miscibility, are presented for a number of representative blends. An emphasis is placed on relating the amorphous miscibility of high‐efficiency PSC blends at a given processing temperature with their actual device performance and stability. It is shown and argued that a system with an amorphous miscibility close to percolation exhibits the most stable morphology. Furthermore, an approach is outlined to convert liquidus miscibility to an effective Flory–Huggins interaction parameter χ. Crucially, determination of temperature‐dependent amorphous miscibility paves a way to rationally optimize the stability and mixing behaviors of PSCs at actual processing and operating temperatures. DA - 2018/10/5/ PY - 2018/10/5/ DO - 10.1002/aenm.201703058 VL - 8 IS - 28 SP - SN - 1614-6840 UR - https://doi.org/10.1002/aenm.201703058 KW - miscibility KW - percolation thresholds KW - polymer solar cells KW - scanning transmission X-ray microscopy ER - TY - JOUR TI - Carboxylate substitution position influencing polymer properties and enabling non-fullerene organic solar cells with high open circuit voltage and low voltage loss AU - Liu, Jing AU - Ma, Lik-Kuen AU - Sheong, Fu Kit AU - Zhang, Lin AU - Hu, Huawei AU - Zhang, Jing-Xuan AU - Zhang, Jianquan AU - Li, Zhengke AU - Ma, Chao AU - Han, Xu AU - Pan, Ding AU - Ade, Harald AU - Ma, Wei AU - Yan, He T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - A novel polymer P3TAE enables a high VOC of 1.20 V and a PCE of 8.10% for non-fullerene OSCs. DA - 2018/9/21/ PY - 2018/9/21/ DO - 10.1039/c8ta04935a VL - 6 IS - 35 SP - 16874-16881 SN - 2050-7496 ER - TY - JOUR TI - Effect of Ring-Fusion on Miscibility and Domain Purity: Key Factors Determining the Performance of PDI-Based Nonfullerene Organic Solar Cells AU - Hu, Huawei AU - Li, Yunke AU - Zhang, Jianquan AU - Peng, Zhengxing AU - Ma, Lik-kuen AU - Xin, Jingming AU - Huang, Jiachen AU - Ma, Tingxuan AU - Jiang, Kui AU - Zhang, Guangye AU - Ma, Wei AU - Ade, Harald AU - Yan, He T2 - ADVANCED ENERGY MATERIALS AB - Abstract Compared to the rapid development of nonfullerene organic solar cells (OSCs) based on the state‐of‐the‐art indacenodithiophene (IDT)‐based small molecule acceptors (SMAs), the progress for perylene diimide (PDI)‐based electron acceptors has lagged behind owing to the lack of understanding on the structure–morphology–performance relationship of PDI SMAs. Given the ease of synthesis for PDIs and their high intrinsic electron mobility, it is crucial to identify key material parameters that influence the polymer:PDI blend morphology and to develop rational approaches for molecular design toward high‐performance PDI‐based SMAs. In this study, three pairs of PDI‐based SMAs with and without ring‐fusion are investigated and it is found that ring‐fusion and domain purity are the key structural and morphological factors determining the fill factors (FFs) and efficiencies of PDI‐based nonfullerene OSCs. This data shows that nonfullerene OSCs based on the ring‐fused PDI‐based SMAs exhibit much higher average domain purity and thus increased charge mobilities, which lead to enhanced FFs compared to those solar cells based on nonfused PDIs. This is explained by higher Florry Huggins interaction parameters as observed by melting point depression measurements. This study suggests that increasing repulsive molecular interactions to lower the miscibility between the polymer donor and PDI acceptor is the key to improve the FF and performance of PDI‐based devices. DA - 2018/9/14/ PY - 2018/9/14/ DO - 10.1002/aenm.201800234 VL - 8 IS - 26 SP - SN - 1614-6840 KW - average domain purity KW - miscibility KW - nonfullerene organic solar cells KW - perylene diimide KW - ring fusion ER - TY - JOUR TI - Modulation of End Groups for Low-Bandgap Nonfullerene Acceptors Enabling High-Performance Organic Solar Cells AU - Chen, Yuzhong AU - Liu, Tao AU - Hu, Huawei AU - Ma, Tingxuan AU - Lai, Joshua Yuk Lin AU - Zhang, Jianquan AU - Ade, Harald AU - Yan, He T2 - ADVANCED ENERGY MATERIALS AB - Abstract The field of nonfullerene organic solar cells (OSCs) has seen an impressive progress, largely due to advances in high‐performance small molecule acceptors (SMAs). As a large portion of the solar energy is located in the near‐infrared region, it is important to develop ultralow‐bandgap SMAs that have extended absorption in the spectral range of 800–1000 nm to maximize light absorption and efficiencies. In this work, three low‐bandgap SMAs, namely, IXIC, IXIC‐2Cl, and IXIC‐4Cl, are designed and synthesized with same fused terthieno[3,2‐ b ]thiophene donor unit and different end groups (EGs). The three SMAs all have low optical bandgap ( E g ) of 1.35, 1.30, and 1.25 eV, respectively. The chlorination on EGs can lower the energy level and broaden absorption range of the SMAs. As a result, the V oc of the devices is reduced but the J sc is significantly increased. In addition, the addition of chlorine atoms can enhance π–π stacking and crystallinity of the SMAs, which result in high fill factors. Overall, the optimum EGs are monochlorine‐substituted IC and OSCs based on PBDB‐T:IXIC‐2Cl that can achieve remarkable power conversion efficiencies (PCEs) of 12.2%, which is one of the highest PCEs for nonfullerene organic solar cells based on low‐bandgap SMAs. DA - 2018/9/25/ PY - 2018/9/25/ DO - 10.1002/aenm.201801203 VL - 8 IS - 27 SP - SN - 1614-6840 KW - end groups KW - low-bandgap small molecule acceptors KW - near-infrared KW - organic solar cells ER - TY - JOUR TI - Shear-Enhanced Transfer Printing of Conducting Polymer Thin Films AU - Sen, Pratik AU - Xiong, Yuan AU - Zhang, Qanqian AU - Park, Sungjune AU - You, Wei AU - Ade, Harald AU - Kudenov, Michael W. AU - Brendan T. O'Connor, T2 - ACS APPLIED MATERIALS & INTERFACES AB - Polymer conductors that are solution-processable provide an opportunity to realize low-cost organic electronics. However, coating sequential layers can be hindered by poor surface wetting or dissolution of underlying layers. This has led to the use of transfer printing where solid film inks are transferred from a donor substrate to partially fabricated devices using a stamp. This approach typically requires favorable adhesion differences between the stamp, ink, and receiving substrate. Here, we present a shear-assisted organic printing (SHARP) technique that employs a shear load on a post-less polydimethylsiloxane (PDMS) elastomer stamp to print large-area polymer films that can overcome large unfavorable adhesion differences between the stamp and receiving substrate. We explore the limits of this process by transfer printing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films with varied formulation that tune the adhesive fracture energy. Using this platform, we show that the SHARP process is able to overcome a 10-fold unfavorable adhesion differential without the use of a patterned PDMS stamp, enabling large-area printing. The SHARP approach is then used to print PEDOT:PSS films in the fabrication of high-performance semitransparent organic solar cells. DA - 2018/9/19/ PY - 2018/9/19/ DO - 10.1021/acsami.8b09968 VL - 10 IS - 37 SP - 31560-31567 SN - 1944-8244 KW - transfer printing KW - adhesion KW - PEDOT:PSS KW - surfactant KW - organic photovoltaics ER - TY - JOUR TI - Sub-Band Gap Turn-On Near-Infrared-to-Visible Up-Conversion Device Enabled by an Organic?Inorganic Hybrid Perovskite Photovoltaic Absorber AU - Yu, Hyeonggeun AU - Cheng, Yuanhang AU - Li, Menglin AU - Tsang, Sai-Wing AU - So, Franky T2 - ACS APPLIED MATERIALS & INTERFACES AB - Direct integration of an infrared (IR) photodetector with an organic light-emitting diode (OLED) enables low-cost, pixel-free IR imaging. However, the operation voltage of the resulting IR-to-visible up-conversion is large because of the series device architecture. Here, we report a low-voltage near-IR (NIR)-to-visible up-conversion device using formamidinium lead iodide as a NIR absorber integrated with a phosphorescent OLED. Because of the efficient photocarrier injection from the hybrid perovskite layer to the OLED, we observed a sub-band gap turn-on of the OLED under NIR illumination. The device showed a NIR-to-visible up-conversion efficiency of 3% and a luminance on/off ratio of 103 at only 5 V. Finally, we demonstrate pixel-free NIR imaging using the up-conversion device. DA - 2018/5/9/ PY - 2018/5/9/ DO - 10.1021/acsami.8b00592 VL - 10 IS - 18 SP - 15920-15925 SN - 1944-8244 KW - organo-halide perovskite KW - infrared imaging KW - up-conversion KW - organic light-emitting diode KW - photovoltaic ER - TY - JOUR TI - Molecular engineering of perylene-diimide-based polymer acceptors containing heteroacene units for all-polymer solar cells AU - Suranagi, Sanjaykumar R. AU - Singh, Ranbir AU - Kim, Joo-Hyun AU - Kim, Min AU - Ade, Harald AU - Cho, Kilwon T2 - ORGANIC ELECTRONICS AB - Polymer acceptors based on perylene diimide (PDI) with three symmetrical S-heteroacene backbone units of different sizes were synthesized for use in all-polymer solar cells (all-PSCs). The effects of varying the size of the heteroacene unit on the backbone of the PDI polymer are evident in the absorption spectra and their energy level offsets, which are correlated with their morphological and photovoltaic properties. These newly synthesized polymers were employed as acceptors with the polymer poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)] (PPDT2FBT) as the donor in all-PSCs that were found to exhibit modest power conversion efficiencies. The variations in photovoltaic properties of all-PSCs are investigated by characterizing the charge generation, carrier mobilities and recombination. The morphological disorder at the polymer/PPDT2FBT interface and average composition variations are revealed by using grazing incidence wide angle X-ray scattering (GIWAXS) and resonance soft X-ray scattering (R-SoXS) characterizations. DA - 2018/7// PY - 2018/7// DO - 10.1016/j.orgel.2018.02.015 VL - 58 SP - 222-230 SN - 1878-5530 KW - Perylene-diimide KW - All-polymer solar cell KW - Bulk-heterojunction KW - Resonance soft X-ray scattering ER - TY - JOUR TI - High-Efficiency All-Small-Molecule Organic Solar Cells Based on an Organic Molecule Donor with Alkylsilyl-Thienyl Conjugated Side Chains AU - Bin, Haijun AU - Yao, Jia AU - Yang, Yankang AU - Angunawela, Indunil AU - Sun, Chenkai AU - Gao, Liang AU - Ye, Long AU - Qiu, Beibei AU - Xue, Lingwei AU - Zhu, Chenhui AU - Yang, Chunhe AU - Zhang, Zhi-Guo AU - Ade, Harald AU - Li, Yongfang T2 - ADVANCED MATERIALS AB - Abstract Two medium‐bandgap p‐type organic small molecules H21 and H22 with an alkylsily‐thienyl conjugated side chain on benzo[1,2‐ b :4,5‐ b ′]dithiophene central units are synthesized and used as donors in all‐small‐molecule organic solar cells (SM‐OSCs) with a narrow‐bandgap n‐type small molecule 2,2′‐((2Z,2′Z)‐((4,4,9,9‐tetrahexyl‐4,9‐dihydro‐ s ‐indaceno[1,2‐ b :5,6‐ b ′]dithiophene‐2,7‐diyl)bis(methanylylidene))bis(3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (IDIC) as the acceptor. In comparison to H21 with 3‐ethyl rhodanine as the terminal group, H22 with cyanoacetic acid esters as the terminal group shows blueshifted absorption, higher charge‐carrier mobility and better 3D charge pathway in blend films. The power conversion efficiency (PCE) of the SM‐OSCs based on H22:IDIC reaches 10.29% with a higher open‐circuit voltage of 0.942 V and a higher fill factor of 71.15%. The PCE of 10.29% is among the top efficiencies of nonfullerene SM‐OSCs reported in the literature to date. DA - 2018/7/5/ PY - 2018/7/5/ DO - 10.1002/adma.201706361 VL - 30 IS - 27 SP - SN - 1521-4095 KW - alkylsilyl-thienyl conjugated side-chains KW - organic small-molecule donor materials KW - organic solar cells ER - TY - JOUR TI - Flexoelectricity in a metal/ferroelectric/semiconductor heterostructure AU - Huang, Shujin AU - Yau, Hei-Man AU - Yu, Hyeonggeun AU - Qi, Lu AU - So, Franky AU - Dai, Ji-Yan AU - Jiang, Xiaoning T2 - AIP ADVANCES AB - The flexoelectricity in a 100 nm-thick BaTiO3 (BTO) thin film based metal/ferroelectric insulator/semiconductor (MFS) heterostructure was reported in this letter. The transverse flexoelectric coefficient of the BTO thin film in the heterojunction structure was measured to be 287-418 μC/m at room temperature, and its temperature dependence shows that the flexoelectric effect in the BTO thin film was dominated in the paraelectric phase. We showed that the BTO thin film capacitance could be controlled at multi-levels by introducing ferroelectric and flexoelectric polarization in the film. These results are promising for understanding of the flexoelectricity in epitaxial ferroelectric thin films and practical applications of the enhanced flexoelectricity in nanoscale devices. DA - 2018/6// PY - 2018/6// DO - 10.1063/1.5031162 VL - 8 IS - 6 SP - SN - 2158-3226 ER - TY - JOUR TI - Every Atom Counts: Elucidating the Fundamental Impact of Structural Change in Conjugated Polymers for Organic Photovoltaics AU - Lo, Chi Kin AU - Gautam, Bhoj R. AU - Selter, Philipp AU - Zheng, Zilong AU - Oosterhout, Stefan D. AU - Constantinou, Iordania AU - Knitsch, Robert AU - Wolfe, Rylan M. W. AU - Yi, Xueping AU - Bredas, Jean-Luc AU - So, Franky AU - Toney, Michael F. AU - Coropceanu, Veaceslav AU - Hansen, Michael Ryan AU - Gundogdu, Kenan AU - Reynolds, John R. T2 - CHEMISTRY OF MATERIALS AB - As many conjugated polymer-based organic photovoltaic (OPV) materials provide substantial solar power conversion efficiencies (as high as 13%), it is important to develop a deeper understanding of how the primary repeat unit structures impact device performance. In this work, we have varied the group 14 atom (C, Si, Ge) at the center of a bithiophene fused ring to elucidate the impact of a minimal repeat unit structure change on the optical, transport, and morphological properties, which ultimately control device performance. Careful polymerization and polymer purification produced three “one-atom change” donor–acceptor conjugated alternating copolymers with similar molecular weights and dispersities. DFT calculation, absorption spectroscopy, and high-temperature solution 1H nuclear magnetic resonance (NMR) results indicate that poly(dithienosilole-alt-thienopyrrolodione), P(DTS-TPD), and poly(dithienogermole-alt-thienopyrrolodione), P(DTG-TPD) exhibit different rotational conformations when compared to poly(cyclopentadithiophene-alt-thienopyrrolodione), P(DTC-TPD). Solid-state 1H MAS NMR experiments reveal that the greater probability of the anticonformation in P(DTS-TPD) and P(DTG-TPD) prevail in the solid phase. The conformational variation seen in solution and solid-state NMR in turn affects the polymer stacking and intermolecular interaction. Two-dimension 1H-1H DQ-SQ NMR correlation spectra shows aromatic–aromatic correlations for P(DTS-TPD) and P(DTG-TPD), which on the other hand is absent for P(DTC-TPD). In a thin-film interchain packing study using grazing incidence wide-angle X-ray scattering (GIWAXS), we observe the π-face of the conjugated backbones of P(DTC-TPD) aligned edge-on to the substrate, whereas in contrast the π-faces of P(DTS-TPD) and P(DTG-TPD) align parallel to the surface. These differences in polymer conformations and backbone orientations lead to variations in the OPV performance of blends with the fullerene PC71BM, with the device containing P(DTC-TPD):PCBM having a lower fill factor and a lower power conversion efficiency. Ultrafast transient absorption spectroscopy shows the P(DTC-TPD):PCBM blend to have a more pronounced triplet formation from bimolecular recombination of initially separated charges. With a combination of sub-bandgap external quantum efficiency measurements and DFT calculations, we present evidence that the greater charge recombination loss is the result of a lower lying triplet energy level for P(DTC-TPD), leading to a higher rate of recombination and lower OPV device performance. Importantly, this study ties ultimate photovoltaic performance to morphological features in the active films that are induced from the processing solution and are a result of minimal one-atom differences in polymer repeat unit structure. DA - 2018/5/8/ PY - 2018/5/8/ DO - 10.1021/acs.chemmater.8b00590 VL - 30 IS - 9 SP - 2995-3009 SN - 1520-5002 ER - TY - JOUR TI - A Wide Band Gap Polymer with a Deep Highest Occupied Molecular Orbital Level Enables 14.2% Efficiency in Polymer Solar Cells AU - Li, Sunsun AU - Ye, Long AU - Zhao, Wenchao AU - Yan, Hongping AU - Yang, Bei AU - Liu, Delong AU - Li, Wanning AU - Ade, Harald AU - Hou, Jianhui T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - To simultaneously achieve low photon energy loss (Eloss) and broad spectral response, the molecular design of the wide band gap (WBG) donor polymer with a deep HOMO level is of critical importance in fullerene-free polymer solar cells (PSCs). Herein, we developed a new benzodithiophene unit, i.e., DTBDT-EF, and conducted systematic investigations on a WBG DTBDT-EF-based donor polymer, namely, PDTB-EF-T. Due to the synergistic electron-withdrawing effect of the fluorine atom and ester group, PDTB-EF-T exhibits a higher oxidation potential, i.e., a deeper HOMO level (ca. −5.5 eV) than most well-known donor polymers. Hence, a high open-circuit voltage of 0.90 V was obtained when paired with a fluorinated small molecule acceptor (IT-4F), corresponding to a low Eloss of 0.62 eV. Furthermore, side-chain engineering demonstrated that subtle side-chain modulation of the ester greatly influences the aggregation effects and molecular packing of polymer PDTB-EF-T. With the benefits of the stronger interchain π–π interaction, the improved ordering structure, and thus the highest hole mobility, the most symmetric charge transport and reduced recombination are achieved for the linear decyl-substituted PDTB-EF-T (P2)-based PSCs, leading to the highest short-circuit current density and fill factor (FF). Due to the high Flory–Huggins interaction parameter (χ), surface-directed phase separation occurs in the P2:IT-4F blend, which is supported by X-ray photoemission spectroscopy results and cross-sectional transmission electron microscope images. By taking advantage of the vertical phase distribution of the P2:IT-4F blend, a high power conversion efficiency (PCE) of 14.2% with an outstanding FF of 0.76 was recorded for inverted devices. These results demonstrate the great potential of the DTBDT-EF unit for future organic photovoltaic applications. DA - 2018/6/13/ PY - 2018/6/13/ DO - 10.1021/jacs.8b02695 VL - 140 IS - 23 SP - 7159-7167 SN - 0002-7863 ER - TY - JOUR TI - Multiple Cases of Efficient Nonfullerene Ternary Organic Solar Cells Enabled by an Effective Morphology Control Method AU - Jiang, Kui AU - Zhang, Guangye AU - Yang, Guofang AU - Zhang, Jianquan AU - Li, Zhengke AU - Ma, Tingxuan AU - Hu, Huawei AU - Ma, Wei AU - Ade, Harald AU - Yan, He T2 - ADVANCED ENERGY MATERIALS AB - Abstract Ternary organic solar cells (OSCs) have attracted much research attention, as they can maintain the simplicity of the single‐junction device architecture while broadening the absorption range of OSCs. However, one main challenge that limits the development of ternary OSCs is the difficulty in controlling the morphology of ternary OSCs. In this paper, an effective approach to control the morphology is presented that leads to multiple cases of efficient nonfullerene ternary OSCs with efficiencies of up to 11.2%. This approach is based on a donor polymer with strong temperature dependent aggregation properties processed from hot solutions without any solvent additives and a pair of small molecular acceptors (SMAs) that have similar surface tensions and thus low propensity to form discrete phases. Such a ternary blend exhibits a simplified bulk‐heterojunction morphology that is similar to the morphology of previously reported binary blends. As a result, an almost linear relationship between V OC and film composition is observed for all nonfullerene ternary devices. Meanwhile, by carefully designing a control system with a large interfacial tension, a different phase separation and V OC dependence is demonstrated. This morphology control approach can be applicable to more material systems and accelerates the development of the ternary OSC field. DA - 2018/3/26/ PY - 2018/3/26/ DO - 10.1002/aenm.201701370 VL - 8 IS - 9 SP - SN - 1614-6840 UR - https://doi.org/10.1002/aenm.201701370 KW - morphology KW - non-fullerene KW - organic solar cells KW - photovoltaics KW - surface tension KW - small molecular acceptors KW - ternary blends ER - TY - JOUR TI - Measuring Temperature-Dependent Miscibility for Polymer Solar Cell Blends: An Easily Accessible Optical Method Reveals Complex Behavior AU - Peng, Zhengxing AU - Jiao, Xuechen AU - Ye, Long AU - Li, Sunsun AU - Rech, Jeromy James AU - You, Wei AU - Hou, Jianhui AU - Ade, Harald T2 - CHEMISTRY OF MATERIALS AB - In bulk-heterojunction polymer solar cells (PSC), the molecular-level mixing between conjugated polymer donors and small-molecule acceptors plays a crucial role in obtaining a desirable morphology and good device stability. It has been recently shown that the thermodynamic limit of this mixing can be quantified by the liquidus miscibility, the composition of the small-molecule acceptor in amorphous phases in the presence of small-molecule crystals, and then converted to the Flory–Huggins interaction parameter χ. This conversion maps out the amorphous miscibility. Moreover, the quantitative relations between χ and the fill factor of PSC devices were established recently. However, the commonly used measurement of this liquidus miscibility, scanning transmission X-ray microscopy, is not easily and readily accessible. Here, we delineate a method based on common visible light microscopy and ultraviolet–visible absorption spectroscopy to replace the X-ray measurements. To demonstrate the feasibility of this technique and methodology, a variety of conjugated polymers (PffBT4T-C9C13, PDPP3T PBDT-TS1, PTB7-Th, and FTAZ) and their miscibility with fullerenes or nonfullerene small molecules (PC71BM, PC61BM, and EH-IDTBR) are characterized. The establishment of this methodology will pave the way to a wider use of the liquidus miscibility and the critical miscibility-function relations to optimize the device performance and obtain good stability in PSCs and other devices. DA - 2018/6/26/ PY - 2018/6/26/ DO - 10.1021/acs.chemmater.8b00889 VL - 30 IS - 12 SP - 3943-3951 SN - 1520-5002 ER - TY - JOUR TI - Alkyl Chain Regiochemistry of Benzotriazole-Based Donor Polymers Influencing Morphology and Performances of Non-Fullerene Organic Solar Cells AU - Chen, Shangshang AU - Zhang, Lin AU - Ma, Chao AU - Meng, Dong AU - Zhang, Jianquan AU - Zhang, Guangye AU - Li, Zhengke AU - Chow, Philip C. Y. AU - Ma, Wei AU - Wang, Zhaohui AU - Wong, Kam Sing AU - Ade, Harald AU - Yan, He T2 - ADVANCED ENERGY MATERIALS AB - Abstract The effects of alkyl chain regiochemistry on the properties of donor polymers and performances of non‐fullerene organic solar cells are investigated. Two donor polymers (PfBTAZ and PfBTAZS) are compared that have nearly identical chemical structures except for the regiochemistry of alkyl chains. The optical properties and crystallinity of two polymers are nearly identical yet the PfBTAZ:O‐IDTBR blend exhibits nearly double domain size compared to the blend based on PfBTAZS:O‐IDTBR. To reveal the origins of the very different domain size of two blends, the morphology of neat polymer films is characterized, and it is found that PfBTAZ tends to aggregate into much larger polymer fibers without the presence of O‐IDTBR. This indicates that it is not the polymer:O‐IDTBR interactions but the intrinsic aggregation properties of two polymers that determine the morphology features of neat and blend films. The stronger aggregation tendency of PfBTAZ could be explained by its more co‐planar geometry of the polymer backbone arising from the different alkyl chain regiochemistry. Combined with the similar trend observed in another set of donor polymers (PTFB‐P and PTFB‐PS), the results provide an important understanding of the structure–property relationships that could guide the development of donor polymers for non‐fullerene organic solar cells. DA - 2018/4/16/ PY - 2018/4/16/ DO - 10.1002/aenm.201702427 VL - 8 IS - 11 SP - SN - 1614-6840 KW - alkyl chains KW - morphology KW - organic solar cells KW - small-molecular acceptors ER - TY - JOUR TI - A High-Efficiency Organic Solar Cell Enabled by the Strong Intramolecular Electron Push-Pull Effect of the Nonfullerene Acceptor AU - Li, Wanning AU - Ye, Long AU - Li, Sunsun AU - Yao, Huifeng AU - Ade, Harald AU - Hou, Jianhui T2 - ADVANCED MATERIALS AB - Besides broadening of the absorption spectrum, modulating molecular energy levels, and other well-studied properties, a stronger intramolecular electron push-pull effect also affords other advantages in nonfullerene acceptors. A strong push-pull effect improves the dipole moment of the wings in IT-4F over IT-M and results in a lower miscibility than IT-M when blended with PBDB-TF. This feature leads to higher domain purity in the PBDB-TF:IT-4F blend and makes a contribution to the better photovoltaic performance. Moreover, the strong push-pull effect also decreases the vibrational relaxation, which makes IT-4F more promising than IT-M in reducing the energetic loss of organic solar cells. Above all, a power conversion efficiency of 13.7% is recorded in PBDB-TF:IT-4F-based devices. DA - 2018/4/19/ PY - 2018/4/19/ DO - 10.1002/adma.201707170 VL - 30 IS - 16 SP - SN - 1521-4095 KW - intramolecular electron push-pull effect KW - miscibility KW - nonfullerene acceptor KW - organic solar cell KW - vibrational relaxation ER - TY - JOUR TI - The Role of FRET in Non-Fullerene Organic Solar Cells: Implications for Molecular Design AU - Gautam, Bhoj R. AU - Younts, Robert AU - Carpenter, Joshua AU - Ade, Harald AU - Gundogdu, Kenan T2 - JOURNAL OF PHYSICAL CHEMISTRY A AB - Non-fullerene acceptors (NFAs) have been demonstrated to be promising candidates for highly efficient organic photovoltaic (OPV) devices. The tunability of absorption characteristics of NFAs can be used to make OPVs with complementary donor–acceptor absorption to cover a broad range of the solar spectrum. However, both charge transfer from donor to acceptor moieties and energy (energy) transfer from high-bandgap to low-bandgap materials are possible in such structures. Here, we show that when charge transfer and exciton transfer processes are both present, the coexistence of excitons in both domains can cause a loss mechanism. Charge separation of excitons in a low-bandgap material is hindered due to exciton population in the larger bandgap acceptor domains. Our results further show that excitons in low-bandgap material should have a relatively long lifetime compared to the transfer time of excitons from higher bandgap material in order to contribute to the charge separation. These observations provide significant guidance for design and development of new materials in OPV applications. DA - 2018/4/19/ PY - 2018/4/19/ DO - 10.1021/acs.jpca.7b12807 VL - 122 IS - 15 SP - 3764-3771 SN - 1089-5639 ER - TY - JOUR TI - Polymer non-fullerene solar cells of vastly different efficiencies for minor side-chain modification: impact of charge transfer, carrier lifetime, morphology and mobility AU - Awartani, Omar M. AU - Gautam, Bhoj AU - Zhao, Wenchao AU - Younts, Robert AU - Hou, Jianhui AU - Gundogdu, Kenan AU - Ade, Harald T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - The performance of the 11.25% efficient PBDB-T : ITIC system degraded to 4.35% after a minor side-chain modification in PBDB-O : ITIC. In this study, the underlying reasons behind this vast difference in efficiencies are investigated. DA - 2018/7/14/ PY - 2018/7/14/ DO - 10.1039/c7ta01746d VL - 6 IS - 26 SP - 12484-12492 SN - 2050-7496 UR - https://doi.org/10.1039/C7TA01746D ER - TY - JOUR TI - Langmuir-Blodgett Thin Films of Diketopyrrolopyrrole-Based Amphiphiles AU - Lo, Chi Kin AU - Wang, Cheng-Yin AU - Oosterhout, Stefan D. AU - Zheng, Zilong AU - Yi, Xueping AU - Fuentes-Hernandez, Canek AU - So, Franky AU - Coropceanu, Veaceslav AU - Bredas, Jean-Luc AU - Toney, Michael F. AU - Kippelen, Bernard AU - Reynolds, John R. T2 - ACS APPLIED MATERIALS & INTERFACES AB - We report on two π-conjugated donor–acceptor–donor (D–A–D) molecules of amphiphilic nature, aiming to promote intermolecular ordering and carrier mobility in organic electronic devices. Diketopyrrolopyrrole was selected as the acceptor moiety that was disubstituted with nonpolar and polar functional groups, thereby providing the amphiphilic structures. This structural design resulted in materials with a strong intermolecular order in the solid state, which was confirmed by differential scanning calorimetry and polarized optical microscopy. Langmuir–Blodgett (LB) films of ordered mono- and multilayers were transferred onto glass and silicon substrates, with layer quality, coverage, and intermolecular order controlled by layer compression pressure on the LB trough. Organic field-effect transistors and organic photovoltaics devices with active layers consisting of the amphiphilic conjugated D–A–D-type molecules were constructed to demonstrate that the LB technique is an effective layer-by-layer deposition approach to fabricate self-assembled, ordered thin films. DA - 2018/4/11/ PY - 2018/4/11/ DO - 10.1021/acsami.7b18239 VL - 10 IS - 14 SP - 11995-12004 SN - 1944-8252 KW - Langmuir-Blodgett KW - monolayer KW - amphiphilic molecules KW - diketopyrrolopyrrole KW - layer-by-layer deposition KW - organic field-effect transistor KW - donor-acceptor-donor molecules ER - TY - JOUR TI - A polymer design strategy toward green solvent processed efficient non-fullerene polymer solar cells AU - Qin, Yunpeng AU - Ye, Long AU - Zhang, Shaoqing AU - Zhu, Jie AU - Yang, Bei AU - Ade, Harald AU - Hou, Jianhui T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - This work suggests an effective material design strategy to prepare efficient PSCs with a green solvent, which is important in PSCs. DA - 2018/3/14/ PY - 2018/3/14/ DO - 10.1039/c8ta00368h VL - 6 IS - 10 SP - 4324-4330 SN - 2050-7496 ER - TY - JOUR TI - Quantitative relations between interaction parameter, miscibility and function in organic solar cells AU - Ye, Long AU - Hu, Huawei AU - Ghasemi, Masoud AU - Wang, Tonghui AU - Collins, Brian A. AU - Kim, Joo-Hyun AU - Jiang, Kui AU - Carpenter, Joshua H. AU - Li, Hong AU - Li, Zhengke AU - McAfee, Terry AU - Zhao, Jingbo AU - Chen, Xiankai AU - Lai, Joshua Lin Yuk AU - Ma, Tingxuan AU - Bredas, Jean-Luc AU - Yan, He AU - Ade, Harald T2 - NATURE MATERIALS DA - 2018/3// PY - 2018/3// DO - 10.1038/s41563-017-0005-1 VL - 17 IS - 3 SP - 253-260 SN - 1476-4660 ER - TY - JOUR TI - Manipulating Refractive Index in Organic Light-Emitting Diodes AU - Salehi, Amin AU - Chen, Ying AU - Fu, Xiangyu AU - Peng, Cheng AU - So, Franky T2 - ACS APPLIED MATERIALS & INTERFACES AB - In a conventional organic light-emitting diode (OLED), only a fraction of light can escape to the glass substrate and air. Most radiation is lost to two major channels: waveguide modes and surface plasmon polaritons. It is known that reducing the refractive indices of the constituent layers in an OLED can enhance light extraction. Among all of the layers, the refractive index of the electron transport layer (ETL) has the largest impact on light extraction because it is the layer adjacent to the metallic cathode. Oblique angle deposition (OAD) provides a way to manipulate the refractive index of a thin film by creating an ordered columnar void structure. In this work, using OAD, the refractive index of tris(8-hydroxyquinoline)aluminum (Alq3) can be tuned from 1.75 to 1.45. With this low-index ETL deposited by OAD, the resulting phosphorescent OLED shows nearly 30% increase in light extraction efficiency. DA - 2018/3/21/ PY - 2018/3/21/ DO - 10.1021/acsami.7b18514 VL - 10 IS - 11 SP - 9595-9601 SN - 1944-8244 KW - organic light-emitting diodes KW - oblique angle deposition KW - spectroscopic ellipsometry KW - refractive index KW - electron transport layer ER - TY - JOUR TI - Integrated circuits based on conjugated polymer monolayer AU - Li, Mengmeng AU - Mangalore, Deepthi Kamath AU - Zhao, Jingbo AU - Carpenter, Joshua H. AU - Yan, Hongping AU - Ade, Harald AU - Yan, He AU - Muellen, Klaus AU - Blom, Paul W. M. AU - Pisula, Wojciech AU - Leeuw, Dago M. AU - Asadi, Kamal T2 - NATURE COMMUNICATIONS AB - It is still a great challenge to fabricate conjugated polymer monolayer field-effect transistors (PoM-FETs) due to intricate crystallization and film formation of conjugated polymers. Here we demonstrate PoM-FETs based on a single monolayer of a conjugated polymer. The resulting PoM-FETs are highly reproducible and exhibit charge carrier mobilities reaching 3 cm2 V-1 s-1. The high performance is attributed to the strong interactions of the polymer chains present already in solution leading to pronounced edge-on packing and well-defined microstructure in the monolayer. The high reproducibility enables the integration of discrete unipolar PoM-FETs into inverters and ring oscillators. Real logic functionality has been demonstrated by constructing a 15-bit code generator in which hundreds of self-assembled PoM-FETs are addressed simultaneously. Our results provide the state-of-the-art example of integrated circuits based on a conjugated polymer monolayer, opening prospective pathways for bottom-up organic electronics. DA - 2018/1/31/ PY - 2018/1/31/ DO - 10.1038/s41467-017-02805-5 VL - 9 SP - SN - 2041-1723 ER - TY - JOUR TI - Surpassing 10% efficiency benchmark for nonfullerene organic solar cells by scalable coating in air from single nonhalogenated solvent AU - Ye, Long AU - Xiong, Y. AU - Zhang, Q. Q. AU - Li, S. S. AU - Wang, C. AU - Jiang, Z. AU - Hou, J. H. AU - You, W. AU - Ade, Harald T2 - Advanced Materials AB - Realizing over 10% efficiency in printed organic solar cells via scalable materials and less toxic solvents remains a grand challenge. In article number 1705485, Harald Ade and co-workers report chlorine-free, in-air blade-coating of a new photoactive combination, FTAZ:IT-M, which is able to yield an efficiency of nearly 11%, despite a high humidity of ≈50%. DA - 2018/// PY - 2018/// DO - 10.1002/adma.201870054 VL - 30 IS - 8 ER - TY - JOUR TI - Influence of Donor Polymer on the Molecular Ordering of Small Molecular Acceptors in Nonfullerene Polymer Solar Cells AU - Hu, Huawei AU - Jiang, Kui AU - Chow, Philip C. Y. AU - Ye, Long AU - Zhang, Guangye AU - Li, Zhengke AU - Carpenter, Joshua H. AU - Ade, Harald AU - Yan, He T2 - ADVANCED ENERGY MATERIALS AB - Abstract Nonfullerene polymer solar cells (PSCs) based on polymer donors and nonfullerene small molecular acceptors (SMAs) have recently attracted considerable attention. Although much of the progress is driven by the development of novel SMAs, the donor polymer also plays an important role in achieving efficient nonfullerene PSCs. However, it is far from clear how the polymer donor choice influences the morphology and performance of the SMAs and the nonfullerene blends. In addition, it is challenging to carry out quantitative analysis of the morphology of polymer:SMA blends, due to the low material contrast and overlapping scattering features of the π–π stacking between the two organic components. Here, a series of nonfullerene blends is studied based on ITIC‐Th blended with five different donor polymers. Through quantitative morphology analysis, the (010) coherence length of the SMA is characterized and a positive correlation between the coherence length of the SMA and the device fill factor (FF) is established. The study reveals that the donor polymer can significantly change the molecular ordering of the SMA and thus improve the electron mobility and domain purity of the blend, which has an overall positive effect that leads to the enhanced device FF for nonfullerene PSCs. DA - 2018/2/15/ PY - 2018/2/15/ DO - 10.1002/aenm.201701674 VL - 8 IS - 5 SP - SN - 1614-6840 KW - coherence length KW - morphology KW - polymer solar cells KW - small molecular acceptor KW - X-ray scattering ER - TY - JOUR TI - High-Performance Wide Bandgap Copolymers Using an EDOT Modified Benzodithiophene Donor Block with 10.11% Efficiency AU - Feng, Kui AU - Yang, Guofang AU - Xu, Xiaopeng AU - Zhang, Guangjun AU - Yan, He AU - Awartani, Omar AU - Ye, Long AU - Ade, Harald AU - Li, Ying AU - Peng, Qiang T2 - ADVANCED ENERGY MATERIALS AB - Abstract Newly developed benzo[1,2‐b:4,5‐b′]dithiophene (BDT) block with 3,4‐ethylenedioxythiophene (EDOT) side chains is first employed to build efficient photovoltaic copolymers. The resulting copolymers, PBDTEDOT‐BT and PBDTEDOTFBT, have a large bandgap more than 1.80 eV, which is attributed to the increased steric hindrance between the BDT and EDOT skeletons. Both copolymers possess the satisfied absorptions, low‐lying highest occupied molecular orbital (HOMO) levels and high crystallinity. Using the fluorination strategy, PBDTEDOT‐FBT exhibits a wider and stronger absorption and a deeper HOMO level than those of PBDTEDOT‐BT. PBDTEDOT‐FBT:[6,6]‐Phenyl C 71 butyric acid methyl ester (PC 71 BM) blend also shows the higher hole mobility and better surface morphology compared with the PBDTEDOTBT:PC 71 BM blend. Combination of above advantages, PBDTEDOT‐FBT devices exhibit much higher power conversion efficiency (PCE) of 10.11%, with an improved open circuit voltage (V oc ) of 0.86 V, short circuit current densities (J sc ) of 16.01 mA cm −2 , and fill factor (FF) of 72.6%. This work not only provides a newly efficient candidate of BDT donor block modified with EDOT conjugated side chains, but also achieves high‐performance large bandgap copolymers for polymer solar cells (PSCs) via the synergistic effect of fluorination and side chain engineering strategies. DA - 2018/2/26/ PY - 2018/2/26/ DO - 10.1002/aenm.201602773 VL - 8 IS - 6 SP - SN - 1614-6840 KW - ethylenedioxythiophene (EDOT) KW - fluorination KW - polymer solar cells KW - side chain engineering KW - wide bandgap copolymers ER - TY - JOUR TI - Charge Generation and Recombination in an Organic Solar Cell with Low Energetic Offsets AU - Ran, Niva A. AU - Love, John A. AU - Heiber, Michael C. AU - Jiao, Xuechen AU - Hughes, Michael P. AU - Karki, Akchheta AU - Wang, Ming AU - Brus, Viktor V. AU - Wang, Hengbin AU - Neher, Dieter AU - Ade, Harald AU - Bazan, Guillermo C. AU - Nguyen, Thuc-Quyen T2 - ADVANCED ENERGY MATERIALS AB - Abstract Organic bulk heterojunction (BHJ) solar cells require energetic offsets between the donor and acceptor to obtain high short‐circuit currents ( J SC ) and fill factors ( FF ). However, it is necessary to reduce the energetic offsets to achieve high open‐circuit voltages ( V OC ). Recently, reports have highlighted BHJ blends that are pushing at the accepted limits of energetic offsets necessary for high efficiency. Unfortunately, most of these BHJs have modest FF values. How the energetic offset impacts the solar cell characteristics thus remains poorly understood. Here, a comprehensive characterization of the losses in a polymer:fullerene BHJ blend, PIPCP:phenyl‐C61‐butyric acid methyl ester (PC 61 BM), that achieves a high V OC (0.9 V) with very low energy losses ( E loss = 0.52 eV) from the energy of absorbed photons, a respectable J SC (13 mA cm −2 ), but a limited FF (54%) is reported. Despite the low energetic offset, the system does not suffer from field‐dependent generation and instead it is characterized by very fast nongeminate recombination and the presence of shallow traps. The charge‐carrier losses are attributed to suboptimal morphology due to high miscibility between PIPCP and PC 61 BM. These results hold promise that given the appropriate morphology, the J SC , V OC , and FF can all be improved, even with very low energetic offsets. DA - 2018/2/15/ PY - 2018/2/15/ DO - 10.1002/aenm.201701073 VL - 8 IS - 5 SP - SN - 1614-6840 KW - energetic offset KW - fill factor KW - morphology KW - organic solar cells KW - recombination ER - TY - JOUR TI - A Facile Method to Fine-Tune Polymer Aggregation Properties and Blend Morphology of Polymer Solar Cells Using Donor Polymers with Randomly Distributed Alkyl Chains AU - Yao, Huatong AU - Li, Yunke AU - Hu, Huawei AU - Chow, Philip C. Y. AU - Chen, Shangshang AU - Zhao, Jingbo AU - Li, Zhengke AU - Carpenter, Joshua H. AU - Lai, Joshua Yuk Lin AU - Yang, Guofang AU - Liu, Yuhang AU - Lin, Haoran AU - Ade, Harald AU - Yan, He T2 - ADVANCED ENERGY MATERIALS AB - Abstract The device performance of polymer solar cells (PSCs) is strongly dependent on the blend morphology. One of the strategies for improving PSC performance is side‐chain engineering, which plays an important role in controlling the aggregation properties of the polymers and thus the domain crystallinity/purity of the donor–acceptor blends. In particular, for a family of high‐performance donor polymers with strong temperature‐dependent aggregation properties, the device performances are very sensitive to the size of alkyl chains, and the best device performance can only be achieved with an optimized odd‐numbered alkyl chain. However, the synthetic route of odd‐numbered alkyl chains is costly and complicated, which makes it difficult for large‐scale synthesis. Here, this study presents a facile method to optimize the aggregation properties and blend morphology by employing donor polymers with a mixture of two even‐numbered, randomly distributed alkyl chains. In a model polymer system, this study suggests that the structural and electronic properties of the random polymers comprising a mixture of 2‐octyldodecyl and 2‐decyltetradecyl alkyl chains can be systematically tuned by varying the mixing ratio, and a high power conversion efficiency (11.1%) can be achieved. This approach promotes the scalability of donor polymers and thus facilitates the commercialization of PSCs. DA - 2018/2/26/ PY - 2018/2/26/ DO - 10.1002/aenm.201701895 VL - 8 IS - 6 SP - SN - 1614-6840 KW - fullerene KW - high efficiency KW - polymer solar cells KW - random polymers KW - side-chain engineering ER -