@article{xu_xue_stuard_ade_zhang_yao_li_li_2021, title={Reducing Energy Disorder of Hole Transport Layer by Charge Transfer Complex for High Performance p-i-n Perovskite Solar Cells}, volume={33}, ISSN={["1521-4095"]}, DOI={10.1002/adma.202006753}, abstractNote={Solution-processed organic semiconductor charge-transport layers (OS-CTLs) with high mobility, low trap density, and energy level alignment have dominated the important progress in p–i–n planar perovskite solar cells (pero-SCs). Unfortunately, their inevitable long chains result in weak molecular stacking, which is likely to generate high energy disorder and deteriorate the charge-transport ability of OS-CTLs. Here, a charge-transfer complex (CTC) strategy to reduce the energy disorder in the OS-CTLs by doping an organic semiconductor, 4,4′-(4,8-bis(5-(trimethylsilyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (BDT-Si), in a commercial hole-transport layer (HTL), poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine (PTAA), is proposed. The formation of the CTC makes the PTAA conjugated backbone electron-deficient, resulting in a quinoidal and stiffer character, which is likely to planarize the PTAA backbone and enhance the ordering of the film in nanoscale. The resultant HTL exhibits a reduced energy disorder, which simultaneously promotes hole transport in the HTL, hole extraction at the interface, energy level alignment, and quasi-Fermi level splitting in the device. As a result, the p–i–n planar pero-SCs with optimized HTL exhibit the best power conversion efficiency of 21.87% with good operating stability. This finding demonstrates that the CTC strategy is an effective way to reduce the energy disorder in HTLs and to improve the performance of planar pero-SCs.}, number={13}, journal={ADVANCED MATERIALS}, author={Xu, Guiying and Xue, Rongming and Stuard, Samuel J. and Ade, Harald and Zhang, Chenjie and Yao, Jianlin and Li, Yaowen and Li, Yongfang}, year={2021}, month={Apr} }
 @article{szymanski_henry_stuard_vongsaysy_courtel_vellutini_bertrand_ade_chambon_wantz_2020, title={Balanced Charge Transport Optimizes Industry-Relevant Ternary Polymer Solar Cells}, volume={4}, ISSN={["2367-198X"]}, url={https://doi.org/10.1002/solr.202000538}, DOI={10.1002/solr.202000538}, abstractNote={Bulk heterojunction polymer solar cells based on a novel combination of materials are fabricated using industry-compliant conditions for large area manufacturing. The relatively low-cost polymer PTQ10 is paired with the nonfullerene acceptor 4TIC-4F. Devices are processed using a nonhalogenated solvent to comply with industrial usage in absence of any thermal treatment to minimize the energy footprint of the fabrication. No solvent additive is used. Adding the well-known and low-cost fullerene derivative PC61BM acceptor to this binary blend to form a ternary blend, the power conversion efficiency (PCE) is improved from 8.4% to 9.9% due to increased fill factor (FF) and open-circuit voltage (VOC) while simultaneously improving the stability. The introduction of PC61BM is able to balance the hole–electron mobility in the ternary blends, which is favourable for high FF. This charge transport behavior is correlated with the bulk heterojunction (BHJ) morphology deduced from grazing-incidence wide-angle X-ray scattering (GIWAXS), atomic force microscopy (AFM), and surface energy analysis. In addition, the industrial figure of merit (i-FOM) of this ternary blend is found to increase drastically upon addition of PC61BM due to an increased performance–stability–cost balance.}, number={11}, journal={SOLAR RRL}, publisher={Wiley}, author={Szymanski, Robin and Henry, Reece and Stuard, Samuel and Vongsaysy, Uyxing and Courtel, Stephanie and Vellutini, Luc and Bertrand, Melanie and Ade, Harald and Chambon, Sylvain and Wantz, Guillaume}, year={2020}, month={Nov} }
 @article{lei_seyitliyev_stuard_mendes_dong_fu_chen_he_yi_zhu_et al._2020, title={Efficient Energy Funneling in Quasi-2D Perovskites: From Light Emission to Lasing}, volume={32}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201906571}, abstractNote={Quasi-2D Ruddlesden–Popper halide perovskites with a large exciton binding energy, self-assembled quantum wells, and high quantum yield draw attention for optoelectronic device applications. Thin films of these quasi-2D perovskites consist of a mixture of domains having different dimensionality, allowing energy funneling from lower-dimensional nanosheets (high-bandgap domains) to 3D nanocrystals (low-bandgap domains). High-quality quasi-2D perovskite (PEA)2(FA)3Pb4Br13 films are fabricated by solution engineering. Grazing-incidence wide-angle X-ray scattering measurements are conducted to study the crystal orientation, and transient absorption spectroscopy measurements are conducted to study the charge-carrier dynamics. These data show that highly oriented 2D crystal films have a faster energy transfer from the high-bandgap domains to the low-bandgap domains (<0.5 ps) compared to the randomly oriented films. High-performance light-emitting diodes can be realized with these highly oriented 2D films. Finally, amplified spontaneous emission with a low threshold 4.16 µJ cm−2 is achieved and distributed feedback lasers are also demonstrated. These results show that it is important to control the morphology of the quasi-2D films to achieve efficient energy transfer, which is a critical requirement for light-emitting devices.}, number={16}, journal={ADVANCED MATERIALS}, author={Lei, Lei and Seyitliyev, Dovletgeldi and Stuard, Samuel and Mendes, Juliana and Dong, Qi and Fu, Xiangyu and Chen, Yi-An and He, Siliang and Yi, Xueping and Zhu, Liping and et al.}, year={2020}, month={Apr} }
 @article{kim_kim_gadisa_stuard_nahid_kwon_bae_kim_park_won_et al._2020, title={Morphological-Electrical Property Relation in Cu(In,Ga)(S,Se)(2) Solar Cells: Significance of Crystal Grain Growth and Band Grading by Potassium Treatment}, volume={16}, ISSN={["1613-6829"]}, DOI={10.1002/smll.202003865}, abstractNote={Solution-processed Cu(In,Ga)(S,Se)2 (CIGS) has a great potential for the production of large-area photovoltaic devices at low cost. However, CIGS solar cells processed from solution exhibit relatively lower performance compared to vacuum-processed devices because of a lack of proper composition distribution, which is mainly instigated by the limited Se uptake during chalcogenization. In this work, a unique potassium treatment method is utilized to improve the selenium uptake judiciously, enhancing grain sizes and forming a wider bandgap minimum region. Careful engineering of the bandgap grading structure also results in an enlarged space charge region, which is favorable for electron–hole separation and efficient charge carrier collection. Besides, this device processing approach has led to a linearly increasing electron diffusion length and carrier lifetime with increasing the grain size of the CIGS film, which is a critical achievement for enhancing photocurrent yield. Overall, 15% of power conversion efficiency is achieved in solar cells processed from environmentally benign solutions. This approach offers critical insights for precise device design and processing rules for solution-processed CIGS solar cells.}, number={48}, journal={SMALL}, author={Kim, Joo-Hyun and Kim, Min Kyu and Gadisa, Abay and Stuard, Samuel J. and Nahid, Masrur Morshed and Kwon, Soyeong and Bae, Soohyun and Kim, Byoungwoo and Park, Gi Soon and Won, Da Hye and et al.}, year={2020}, month={Dec} }
 @article{liang_li_wang_qin_stuard_peng_deng_ade_ye_geng_2020, title={Optimization Requirements of Efficient Polythiophene:Nonfullerene Organic Solar Cells}, volume={4}, ISSN={["2542-4351"]}, url={https://publons.com/wos-op/publon/33106087/}, DOI={10.1016/j.joule.2020.04.014}, abstractNote={Summary Polythiophene (PT) and its derivatives have attracted long-standing attention in the organic photovoltaic community for their low cost and high scalability of synthesis. However, due to the lack of rational guidelines in controlling morphology and matching materials, the power conversion efficiencies (PCEs) based on PTs reported so far are generally below 10%. Here, we establish the first-ever relationship between miscibility, morphology, and device performance of binary blends, based on various nonfullerene acceptors (ITIC-Th1, ITIC, IT4F, IDIC, and Y6) and a PT derivative named PDCBT-Cl by scattering and calorimetric characterizations. Benefiting from a properly quenched mixed phase, PDCBT-Cl:ITIC-Th1 system shows the best efficiency of over 12%. Conversely, the blend of PDCBT-Cl and the star acceptor Y6 remained in a homogeneous state due to their high miscibility, resulting in abysmal performance with PCE of 0.5%. Specific guidelines are also proposed to remediate the performance of PDCBT-Cl:Y6, which are crucial for advancing their practical applications.}, number={6}, journal={JOULE}, author={Liang, Ziqi and Li, Miaomiao and Wang, Qi and Qin, Yunpeng and Stuard, Sam J. and Peng, Zhongxiang and Deng, Yunfeng and Ade, Harald and Ye, Long and Geng, Yanhou}, year={2020}, month={Jun}, pages={1278–1295} }
 @article{kang_ye_xu_an_stuard_zhang_yao_ade_hou_2019, title={A Printable Organic Cathode Interlayer Enables over 13% Efficiency for 1-cm(2) Organic Solar Cells}, volume={3}, ISSN={["2542-4351"]}, url={https://publons.com/wos-op/publon/17838771/}, DOI={10.1016/j.joule.2018.10.024}, abstractNote={Summary Currently, most cathode interlayer (CIL) materials for organic solar cells (OSCs) cannot be processed by printing techniques, which severely limits their use in practical productions. Herein, we report a naphthalene diimide (NDI)-based small-molecular compound (N,N-dimethylamino)propyl naphthalene diimide (NDI-N) as printable CIL for OSCs. NDI-N exhibits a unique advantage that combines the merits of high crystallinity and good film-forming property in one material, endowing the semiconductor with excellent electron-transport properties and good processability. By using the NDI-N as CIL, a high power-conversion efficiency (PCE) of 13.9% was achieved in a PBDB-T-2F:IT-4F-based OSC device. More importantly, a large-area OSC device of 1 cm2 was fabricated by using the blade-coated NDI-N CIL and an outstanding PCE of 13.2% was achieved, which represents the highest efficiency of large-area OSCs. The results in this work may pave the way for low-cost and mass production of OSCs.}, number={1}, journal={JOULE}, author={Kang, Qian and Ye, Long and Xu, Bowei and An, Cunbin and Stuard, Samuel J. and Zhang, Shaoqing and Yao, Huifeng and Ade, Harald and Hou, Jianhui}, year={2019}, month={Jan}, pages={227–239} }
 @article{hu_oswald_hu_stuard_nahid_yan_chen_ade_neilson_you_2019, title={Aryl-Perfluoroaryl Interaction in Two-Dimensional Organic-Inorganic Hybrid Perovskites Boosts Stability and Photovoltaic Efficiency}, volume={1}, ISSN={["2639-4979"]}, DOI={10.1021/acsmaterialslett.9b00102}, abstractNote={Two-dimensional (2D) organic–inorganic hybrid perovskites (OIHPs) have showed impressive stability, compared to their three-dimensional (3D) counterparts. However, tuning the chemical structure of the organic cations to simultaneously improve the device performance and stability of 2D OIHP solar cells is rarely reported. Here, we demonstrate that by introducing a classic noncovalent aryl-perfluoroaryl interaction, 2D OIHP solar cells with 1:1 mixed phenethylammonium (PEA) and perfluorophenethylammonium (F5-PEA) can achieve an efficiency of >10% with much enhanced stability using a simple deposition at low temperature without using any additives. The competing effects of surface morphology and crystal orientation with an increased amount of F5-PEA result in the highest efficiency at a 1:1 ratio, while single-crystal studies reveal the expected aryl-perfluoroaryl interaction, accounting for the highest device stability of 2D OIHP solar cell at 1:1 ratio as well. This work provides an example where tuning the interactions of organic cations via molecular engineering can have a profound effect on device performance and stability of 2D OIHP solar cells.}, number={1}, journal={ACS MATERIALS LETTERS}, author={Hu, Jun and Oswald, Iain W. H. and Hu, Huamin and Stuard, Samuel J. and Nahid, Masrur Morshed and Yan, Liang and Chen, Zheng and Ade, Harald and Neilson, James R. and You, Wei}, year={2019}, month={Jul}, pages={171–176} }
 @article{carpenter_ghasemi_gann_angunawela_stuard_rech_ritchie_brendan t. o'connor_atkin_you_et al._2019, title={Competition between Exceptionally Long-Range Alkyl Sidechain Ordering and Backbone Ordering in Semiconducting Polymers and Its Impact on Electronic and Optoelectronic Properties}, volume={29}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201806977}, abstractNote={Intra- and intermolecular ordering greatly impacts the electronic and optoelectronic properties of semiconducting polymers. The interrelationship between ordering of alkyl sidechains and conjugated backbones has yet to be fully detailed, despite much prior effort. Here, the discovery of a highly ordered alkyl sidechain phase in six representative semiconducting polymers, determined from distinct spectroscopic and diffraction signatures, is reported. The sidechain ordering exhibits unusually large coherence lengths (≥70 nm), induces torsional/twisting backbone disorder, and results in a vertically multilayered nanostructure with ordered sidechain layers alternating with disordered backbone layers. Calorimetry and in situ variable temperature scattering measurements in a model system poly{4-(5-(4,8-bis(3-butylnonyl)-6-methylbenzo[1,2-b:4,5-b′]dithiophen-2-yl)thiophen-2-yl)-2-(2-butyloctyl)-5,6-difluoro-7-(5-methylthiophen-2-yl)-2H-benzo[d][1,2,3]triazole} (PBnDT-FTAZ) clearly delineate this competition of ordering that prevents simultaneous long-range order of both moieties. The long-range sidechain ordering can be exploited as a transient state to fabricate PBnDT-FTAZ films with an atypical edge-on texture and 2.5× improved field-effect transistor mobility. The observed influence of ordering between the moieties implies that improved molecular design can produce synergistic rather than destructive ordering effects. Given the large sidechain coherence lengths observed, such synergistic ordering should greatly improve the coherence length of backbone ordering and thereby improve electronic and optoelectronic properties such as charge transport and exciton diffusion lengths.}, number={5}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Carpenter, Joshua H. and Ghasemi, Masoud and Gann, Eliot and Angunawela, Indunil and Stuard, Samuel J. and Rech, Jeromy James and Ritchie, Earl and Brendan T. O'Connor and Atkin, Joanna and You, Wei and et al.}, year={2019}, month={Feb} }
 @article{ghasemi_hu_peng_rech_angunawela_carpenter_stuard_wadsworth_mcculloch_you_et al._2019, title={Delineation of Thermodynamic and Kinetic Factors that Control Stability in Non-fullerene Organic Solar Cells}, volume={3}, ISSN={["2542-4351"]}, DOI={10.1016/j.joule.2019.03.020}, abstractNote={•NF-OSCs with optimal miscibility are intrinsically stable against demixing•Crystallization of NF-SMA needs to be suppressed through proper vitrification•Polymers and NF-SMA with high Tg are needed to achieve long-term OSCs stability In recent years, the performance of organic solar cells (OSCs) has greatly improved with the development of novel non-fullerene small molecular acceptors (NF-SMA). The rapid increase in power conversion efficiency, now surpassing 15%, highlights an immediate and increasing need to understand the longevity and lifetime of NF-OSCs. However, the field relies mainly on a laborious trial-and-error approach to select polymer:NF-SMA pairs with desirable device stability. Here, we provide a structure-property relation that explains the morphological stability and burn-in degradation due to excessive demixing or crystallization. The framework presented in our study shows that a specific balance of interactions between polymer and NF-SMA can offer a short-term solution against excessive demixing. Long-term morphological stability that also suppresses crystallization can only be achieved by freezing in the initial quenched morphology through the use of polymers and/or NF-SMAs with low flexibility. Although non-fullerene small molecular acceptors (NF-SMAs) are dominating current research in organic solar cells (OSCs), measurements of thermodynamics drivers and kinetic factors determining their morphological stability are lacking. Here, we delineate and measure such factors in crystallizable NF-SMA blends and discuss four model systems with respect to their meta-stability and degree of vitrification. We determine for the first time the amorphous-amorphous phase diagram in an NF-SMA system and show that its deep quench depth can result in severe burn-in degradation. We estimate the relative phase behavior of four other materials systems. Additionally, we derive room-temperature diffusion coefficients and conclude that the morphology needs to be stabilized by vitrification corresponding to diffusion constants below 10−22 cm2/s. Our results show that to achieve stability via rational molecular design, the thermodynamics, glass transition temperature, diffusion properties, and related structure-function relations need to be more extensively studied and understood. Although non-fullerene small molecular acceptors (NF-SMAs) are dominating current research in organic solar cells (OSCs), measurements of thermodynamics drivers and kinetic factors determining their morphological stability are lacking. Here, we delineate and measure such factors in crystallizable NF-SMA blends and discuss four model systems with respect to their meta-stability and degree of vitrification. We determine for the first time the amorphous-amorphous phase diagram in an NF-SMA system and show that its deep quench depth can result in severe burn-in degradation. We estimate the relative phase behavior of four other materials systems. Additionally, we derive room-temperature diffusion coefficients and conclude that the morphology needs to be stabilized by vitrification corresponding to diffusion constants below 10−22 cm2/s. Our results show that to achieve stability via rational molecular design, the thermodynamics, glass transition temperature, diffusion properties, and related structure-function relations need to be more extensively studied and understood. The performance of solution-processed organic solar cells (OSCs) based on bulk heterojunction (BHJ) blends of a pair of donor and acceptor materials has greatly improved with the development of novel non-fullerene small molecular acceptors (NF-SMA).1Yan C. Barlow S. Wang Z. Yan H. Jen A.K.-Y. Marder S.R. Zhan X. Non-fullerene acceptors for organic solar cells.Nat. Rev. Mater. 2018; 3: 18003Crossref Scopus (1785) Google Scholar, 2Zhang G. Zhao J. Chow P.C.Y. Jiang K. Zhang J. Zhu Z. Zhang J. Huang F. Yan H. Nonfullerene acceptor molecules for bulk heterojunction organic solar cells.Chem. Rev. 2018; 118: 3447-3507Crossref PubMed Scopus (1160) Google Scholar, 3Li S. Liu W. Li C.Z. Shi M. Chen H. Efficient organic solar cells with non-fullerene acceptors.Small. 2017; 13: 1701120Crossref Scopus (200) Google Scholar, 4Nielsen C.B. Holliday S. Chen H.Y. Cryer S.J. McCulloch I. Non-fullerene electron acceptors for use in organic solar cells.Acc. Chem. 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The stability of NF-SMA OSCs and, importantly, its thermodynamic drivers and mechanical or thermal factors that relate to vitrification, remain largely unexplored. To rationally enhance the operational lifetime of NF-SMA-based OSCs, the factors that control the morphological stability of the active layer need to be investigated and understood in depth. An efficiency loss in the first few hundred hours of the operation of an unstable OSC is generally referred to as “burn-in” and can be caused by various factors such as trap state formation,27Peters C.H. Sachs-Quintana I.T. Mateker W.R. Heumueller T. Rivnay J. Noriega R. Beiley Z.M. Hoke E.T. Salleo A. McGehee M.D. The mechanism of burn-in loss in a high efficiency polymer solar cell.Adv. Mater. 2012; 24: 663-668Crossref PubMed Scopus (217) Google Scholar photo-oxidation and oligomerization,28Burlingame Q. Tong X. Hankett J. Slootsky M. Chen Z. Forrest S.R. 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Burn-in driven by over-purification of mixed domains and/or crystallization have been extensively studied and linked to morphological instability in fullerene-based systems,22Li N. Perea J.D. Kassar T. Richter M. Heumueller T. Matt G.J. Hou Y. Güldal N.S. Chen H. Chen S. et al.Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing.Nat. Commun. 2017; 8: 14541Crossref PubMed Scopus (263) Google Scholar, 30Mendaza A.D. Melianas A. Rossbauer S. Bäcke O. Nordstierna L. Erhart P. Olsson E. Anthopoulos T.D. Inganäs O. Müller C. High-entropy mixtures of pristine fullerenes for solution-processed transistors and solar cells.Adv. Mater. 2015; 27: 7325-7331Crossref PubMed Scopus (45) Google Scholar, 31Lindqvist C. Bergqvist J. Bäcke O. Gustafsson S. Wang E. Olsson E. Inganäs O. Andersson M.R. Müller C. Fullerene mixtures enhance the thermal stability of a non-crystalline polymer solar cell blend.Appl. Phys. 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Horiz. 2014; 1: 270-279Crossref Google Scholar For an amorphous polymer donor and with suppression of the crystallization of the small molecule acceptor (SMA), the phase diagram is asymmetric and there are only two domains: the acceptor-rich small molecule domain that is almost pure in sufficiently immiscible systems, and the donor rich, mixed amorphous domain.37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar In addition to these two domains, a semi-crystalline donor based device has an additional pure polymer crystalline domain. The crystallization of the SMA (fullerene or NF-SMA) is usually prevented in fresh devices by quenching the acceptor into an amorphous, vitrified state.15de Zerio A.D. Müller C. Glass forming acceptor alloys for highly efficient and thermally stable ternary organic solar cells.Adv. Energy Mater. 2018; 8: 1702741Crossref Scopus (69) Google Scholar This two- or three-phase morphology must be carefully optimized to maximize the photon absorption, exciton separation, and charge transportation and extraction simultaneously. Such an optimization often creates mixed domains with an unstable composition (Figure 1).22Li N. Perea J.D. Kassar T. Richter M. Heumueller T. Matt G.J. Hou Y. Güldal N.S. Chen H. Chen S. et al.Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing.Nat. Commun. 2017; 8: 14541Crossref PubMed Scopus (263) Google Scholar, 38Liu Y. Zhao J. Li Z. Mu C. Ma W. Hu H. Jiang K. Lin H. Ade H. Yan H. Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells.Nat. Commun. 2014; 5: 5293Crossref PubMed Scopus (2727) Google Scholar, 39Müller C. On the glass transition of polymer semiconductors and its impact on polymer solar cell stability.Chem. Mater. 2015; 27: 2740-2754Crossref Scopus (179) Google Scholar, 40Ye L. Collins B.A. Jiao X. Zhao J. Yan H. Ade H. Miscibility-function relations in organic solar cells: significance of optimal miscibility in relation to percolation.Adv. Energy Mater. 2018; 8: 1703058Crossref Scopus (194) Google Scholar For crystallizable SMAs, the meta-stable state of the amorphous domains is governed by the binodal composition, also referred to as the miscibility gap.41Rathi P. Huang T.M. Dayal P. Kyu T. Crystalline−amorphous interaction in relation to the phase diagrams of binary polymer blends containing a crystalline constituent.J. Phys. Chem. B. 2008; 112: 6460-6466Crossref PubMed Scopus (37) Google Scholar The thermodynamically favored (stable) state involves SMA crystals, a state described by the liquidus in the phase diagram. This state depletes the mixed domains of SMA relative to the binodal because of the extra chemical potential of the crystals. Please note that we will use the term binodal or miscibility gap and liquidus for simplicity even in cases where the liquid phases have vitrified to an amorphous glass below the glass transition temperature Tg, and the phase boundaries correspond to solid-solid transitions. The binodal or miscibility gap is governed by the miscibility limit of the donor or acceptor materials in the majority phase, which can be parameterized in favorable cases by the effective amorphous-amorphous Flory-Huggins (F-H) interaction parameter χ.42Kouijzer S. Michels J.J. van den Berg M. Gevaerts V.S. Turbiez M. Wienk M.M. Janssen R.A.J. Predicting morphologies of solution processed polymer: fullerene blends.J. Am. Chem. Soc. 2013; 135: 12057-12067Crossref PubMed Scopus (241) Google Scholar, 43Kozub D.R. Vakhshouri K. Orme L.M. Wang C. Hexemer A. Gomez E.D. Polymer crystallization of partially miscible polythiophene/fullerene mixtures controls morphology.Macromolecules. 2011; 44: 5722-5726Crossref Scopus (240) Google Scholar It has been shown recently that the temperature-dependent χ(T) is quantitatively related to the domain purity and fill factor (FF) in a number of systems.37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar A relatively high χ is needed for strong-enough phase separation and, thus, high device FF. However, an excessive repulsive molecular interaction between donor and acceptor materials can lead to over-purification of the mixed domains (i.e., with an SMA concentration below the percolation threshold), which would negatively affect device performance predominantly because of charge trapping and mono-molecular recombination.37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar, 40Ye L. Collins B.A. Jiao X. Zhao J. Yan H. Ade H. Miscibility-function relations in organic solar cells: significance of optimal miscibility in relation to percolation.Adv. Energy Mater. 2018; 8: 1703058Crossref Scopus (194) Google Scholar, 44Bartelt J.A. Beiley Z.M. Hoke E.T. Mateker W.R. Douglas J.D. Collins B.A. Tumbleston J.R. Graham K.R. Amassian A. Ade H. et al.The importance of fullerene percolation in the mixed regions of polymer-fullerene bulk heterojunction solar cells.Adv. Energy Mater. 2013; 3: 364-374Crossref Scopus (406) Google Scholar, 45Ye L. Li S. Liu X. Zhang X. Ghasemi M. Xiong Y. Hou J. Ade H. Quenching to the percolation threshold in organic solar cells.Joule. 2018; 3: 443-458Abstract Full Text Full Text PDF Scopus (142) Google Scholar Schematics of the possible scenarios of morphology evolution in an upper critical solution temperature (UCST) polymer:SMA blend with an amorphous donor and crystallizable SMA with a low and an optimal miscibility are illustrated in Figure 1. Severe burn-in degradation can be expected when the optimal morphology is quenched near the percolation threshold and is far from the miscibility gap, referred to as a “low-” or “hypo-miscibility” system (Figure 1A). On the other hand, a device with a miscibility gap close to the percolation threshold (Figure 1B) during the normal device operation conditions is referred to as “optimal miscibility” and is expected to exhibit a relatively stable morphology and thus lower or slower burn-in degradation. Hyper-miscibility systems typically yield low performance37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar and are not further considered. One example of a hypo-miscibility, high-performing polymer:SMA blend system (as illustrated in Figure 1A) is PffBT4T-2OD:PC71BM, with a PC71BM meta-stable equilibrium concentration in the mixed domains well below the percolation threshold.38Liu Y. Zhao J. Li Z. Mu C. Ma W. Hu H. Jiang K. Lin H. Ade H. Yan H. Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells.Nat. Commun. 2014; 5: 5293Crossref PubMed Scopus (2727) Google Scholar, 40Ye L. Collins B.A. Jiao X. Zhao J. Yan H. Ade H. Miscibility-function relations in organic solar cells: significance of optimal miscibility in relation to percolation.Adv. Energy Mater. 2018; 8: 1703058Crossref Scopus (194) Google Scholar Consequently, abnormally strong burn-in degradation is observed in PffBT4T-2OD:PC71BM solar cells as [6,6]-phenyl C61 or C71 butyric acid methyl ester (PCBM) readily diffuses even at RT.22Li N. Perea J.D. Kassar T. Richter M. Heumueller T. Matt G.J. Hou Y. Güldal N.S. Chen H. Chen S. et al.Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing.Nat. Commun. 2017; 8: 14541Crossref PubMed Scopus (263) Google Scholar In contrast, PCDTBT:PC71BM is a near optimally miscible system, which should provide improved shelf stability with regard to demixing of the mixed domain when compared to PffBT4T-2OD:PC71BM.37Ye L. Hu H. Ghasemi M. Wang T. Collins B.A. Kim J.H. Jiang K. Carpenter J.H. Li H. Li Z. et al.Quantitative relations between interaction parameter, miscibility and function in organic solar cells.Nat. Mater. 2018; 17: 253-260Crossref PubMed Scopus (432) Google Scholar However, PCDTBT:PC61BM blends, similar to other fullerene-based OSCs, are prone to crystallization of the fullerene, and although these blends are thermodynamically stabilized against amorphous demixing, they are only kinetically stabilized against degradation by crystallization, the second main morphological degradation pathway.46Li Z. Ho Chiu K. Shahid Ashraf R. Fearn S. Dattani R. Cheng Wong H. Tan C.H. Wu J. Cabral J.T. Durrant J.R. Toward improved lifetimes of organic solar cells under thermal stress: substrate-dependent morphological stability of PCDTBT: PCBM films and devices.Sci. Rep. 2015; 5: 15149Crossref PubMed Scopus (46) Google Scholar, 47Wong H.C. Li Z. Tan C.H. Zhong H. Huang Z. Bronstein H. McCulloch I. Cabral J.T. Durrant J.R. Morphological stability and performance of polymer–fullerene solar cells under thermal stress: the impact of photoinduced PC60BM oligomerization.ACS Nano. 2014; 8: 1297-1308Crossref PubMed Scopus (115) Google Scholar It is known that thermal annealing can boost the efficiency of many OSCs; however, heating may accelerate the transition of the morphology from the meta-stable miscibility gap to the liquidus or directly and simultaneously lead to crystallization failure as a result of nucleation or growth of SMA crystals.15de Zerio A.D. Müller C. Glass forming acceptor alloys for highly efficient and thermally stable ternary organic solar cells.Adv. Energy Mater. 2018; 8: 1702741Crossref Scopus (69) Google Scholar The propensity for this transition to occur will depend on Tg, which is an indicator of the degree of vitrification at RT. Conceptually, there are three main classes of systems for crystallizable NF-SMA: class I systems that are unstable as a result of demixing and crystallization (low Tg case in Figure 1A), class II systems that have meta-stable mixed domains but can crystallize (low Tg case in Figure 1B), and class III systems that are kinetically stabilized irrespective of whether they are meta-stable or not (high Tg cases). Class III can be subdivided into class IIIa when a hypo-miscibility system is vitrified and class IIIb when an optimal miscibility, meta-stable system is vitrified. In Figure 1, we measure the phase diagrams of NF-SMA OSC systems for the first time at least partially and delineate thermodynamic drivers and kinetic factors for stability in the three main classes of NF-SMA OSC systems delineated above. We select and utilize the well-known, prototypical NF-SMAs (i.e., EH-IDTBR and ITIC) selectively blended with the prototypical semiconductor polymers P3HT (semi-crystalline, ductile) and FTAZ (amorphous, ductile) to yield three different donor-acceptor blend-based systems in this study (P3HT:EH-IDTBR, FTAZ:EH-IDTBR, and FTAZ:ITIC) that systematically exemplify the characteristics of the different scenarios. We determine their device morphology and operational shelf-stability for variable processing conditions. We also investigate the thermodynamic drivers and kinetic factors of a previously reported relatively stable NF-SMA system based on another prototypical amorphous donor, namely PTB7-Th:EH-IDTBR,19Baran D. Gasparini N. Wadsworth A. Tan C.H. Wehbe N. Song X. Hamid Z. Zhang W. Neophytou M. Kirchartz T. et al.Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination.Nat. Commun. 2018; 9: 2059Crossref PubMed Scopus (134) Google Scholar as a comparison (the 4th system). It is found that P3HT:EH-IDTBR-based OSCs suffer from severe burn-in degradation in both as-cast and annealed samples. The severe efficiency loss of P3HT:EH-IDTBR devices is more pronounced in annealed devices compared to as-cast devices, even when these films are only briefly annealed at moderately elevated temperatures (120°C for 10 min). Even short periods of annealing are sufficient to nucleate crystals of the NF-SMA, which then assert their presence and negative influence over time. On the other hand, as-cast blend films based on FTAZ:EH-IDTBR exhibit low burn-in loss, whereas strong burn-in degradation occurs readily in annealed FTAZ:EH-IDTBR devices. In contrast, by substituting EH-IDTBR with ITIC, the FTAZ:ITIC-based systems provide OSCs with reduced burn-in degradation in both as-cast and low temperature annealed (120°C) devices, but with severe burn-in in high T annealed (180°C) devices. We determine χ(T) for P3HT:EH-IDTBR, the liquidus for FTAZ:EH-IDTBR, and FTAZ:ITIC-based systems, and the binodal at 110°C and 100°C for PTB7-Th:EH-IDTBR. In addition, we estimated RT diffusion coefficients of 1.7 × 10−17, 2.0 × 10−18, and 4 × 10−20 cm2/s for EH-IDTBR in P3HT, FTAZ, and PTB7-Th, respectively, and analyzed device stability in light of the thermodynamic and kinetic knowledge gained. The diffusion coefficient of EH-IDTBR in P3HT- and FTAZ-based systems is sufficiently high to enable demixing and crystallization burn-in after low T annealing or even in as-cast devices. The more robust morphology of PTB7-Th:EH-IDTBR devices is attributed to the smaller diffusion coefficient of EH-IDTBR in PTB7-Th. These results indicate that NF-SMA OSCs can be stabilized by employing an NF-SMA with a high Tg or a polymer with lower ductility that suppresses the crystallization of the NF-SMA. In order for NF-SMA-based OSCs to be a viable technology, the quenched morphology that gives high performance has to be stabilized against demixing or crystallization by a high degree of vitrification with low diffusion (∼1 × 10−22 cm2/s) or systems have to be meta-stable with a mixed composition near the percolation threshold, and the crystallization of the NF-SMA has to be suppressed or intr}, number={5}, journal={JOULE}, author={Ghasemi, Masoud and Hu, Huawei and Peng, Zhengxing and Rech, Jeromy James and Angunawela, Indunil and Carpenter, Joshua H. and Stuard, Samuel J. and Wadsworth, Andrew and McCulloch, Iain and You, Wei and et al.}, year={2019}, month={May}, pages={1328–1348} }
 @article{hu_ye_ghasemi_balar_rech_stuard_you_brendan t. o'connor_ade_2019, title={Highly Efficient, Stable, and Ductile Ternary Nonfullerene Organic Solar Cells from a Two-Donor Polymer Blend}, volume={31}, ISSN={["1521-4095"]}, url={https://publons.com/wos-op/publon/18518240/}, DOI={10.1002/adma.201808279}, abstractNote={Organic solar cells (OSCs) are one of the most promising cost-effective options for utilizing solar energy, and, while the field of OSCs has progressed rapidly in device performance in the past few years, the stability of nonfullerene OSCs has received less attention. Developing devices with both high performance and long-term stability remains challenging, particularly if the material choice is restricted by roll-to-roll and benign solvent processing requirements and desirable mechanical durability. Building upon the ink (toluene:FTAZ:IT-M) that broke the 10% benchmark when blade-coated in air, a second donor material (PBDB-T) is introduced to stabilize and enhance performance with power conversion efficiency over 13% while keeping toluene as the solvent. More importantly, the ternary OSCs exhibit excellent thermal stability and storage stability while retaining high ductility. The excellent performance and stability are mainly attributed to the inhibition of the crystallization of nonfullerene small-molecular acceptors (SMAs) by introducing a stiff donor that also shows low miscibility with the nonfullerene SMA and a slightly higher highest occupied molecular orbital (HOMO) than the host polymer. The study indicates that improved stability and performance can be achieved in a synergistic way without significant embrittlement, which will accelerate the future development and application of nonfullerene OSCs.}, number={17}, journal={ADVANCED MATERIALS}, publisher={Wiley}, author={Hu, Huawei and Ye, Long and Ghasemi, Masoud and Balar, Nrup and Rech, Jeromy James and Stuard, Samuel J. and You, Wei and Brendan T. O'Connor and Ade, Harald}, year={2019}, month={Apr} }
 @article{hu_oswald_stuard_nahid_zhou_williams_guo_yan_hu_chen_et al._2019, title={Synthetic control over orientational degeneracy of spacer cations enhances solar cell efficiency in two-dimensional perovskites}, volume={10}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-019-08980-x}, abstractNote={Abstract Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. Chemical tuning of spacer organic cations has attracted great interest due to their additional functionalities. However, how the chemical nature of the organic cations affects the properties of two-dimensional perovskites and devices is rarely reported. Here we demonstrate that the selection of spacer cations (i.e., selective fluorination of phenethylammonium) affects the film properties of two-dimensional perovskites, leading to different device performance of two-dimensional perovskite solar cells (average n = 4). Structural analysis reveals that different packing arrangements and orientational disorder of the spacer cations result in orientational degeneracy and different formation energies, largely explaining the difference in film properties. This work provides key missing information on how spacer cations exert influence on desirable electronic properties and device performance of two-dimensional perovskites via the weak and cooperative interactions of these cations in the crystal lattice.}, journal={NATURE COMMUNICATIONS}, author={Hu, Jun and Oswald, Iain W. H. and Stuard, Samuel J. and Nahid, Masrur Morshed and Zhou, Ninghao and Williams, Olivia F. and Guo, Zhenkun and Yan, Liang and Hu, Huamin and Chen, Zheng and et al.}, year={2019}, month={Mar} }
 @article{lin_fang_zhao_shao_stuard_nahid_ade_wang_shield_zhou_et al._2019, title={Unveiling the operation mechanism of layered perovskite solar cells}, volume={10}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-019-08958-9}, abstractNote={Abstract Layered perovskites have been shown to improve the stability of perovskite solar cells while its operation mechanism remains unclear. Here we investigate the process for the conversion of light to electrical current in high performance layered perovskite solar cells by examining its real morphology. The layered perovskite films in this study are found to be a mixture of layered and three dimensional (3D)-like phases with phase separations at micrometer and nanometer scale in both vertical and lateral directions. This phase separation is explained by the surface initiated crystallization process and the competition of the crystallization between 3D-like and layered perovskites. We further propose that the working mechanisms of the layered perovskite solar cells involve energy transfer from layered to 3D-like perovskite network. The impact of morphology on efficiency and stability of the hot-cast layered perovskite solar cells are also discussed to provide guidelines for the future improvement.}, journal={NATURE COMMUNICATIONS}, author={Lin, Yun and Fang, Yanjun and Zhao, Jingjing and Shao, Yuchuan and Stuard, Samuel J. and Nahid, Masrur Morshed and Ade, Harald and Wang, Qi and Shield, Jeffrey E. and Zhou, Ninghao and et al.}, year={2019}, month={Mar} }