@article{steckmann_angunawela_kashani_zhu_nahid_ade_gadisa_2022, title={Ultrathin P(NDI2OD-T2) Films with High Electron Mobility in Both Bottom-Gate and Top-Gate Transistors}, volume={3}, ISSN={["2199-160X"]}, url={https://doi.org/10.1002/aelm.202101324}, DOI={10.1002/aelm.202101324}, abstractNote={Ultrathin organic films (typically < 10 nm) attracted great attention due to their (semi)transparency and unique optoelectronic properties that benefit applications such as sensors and flexible electronics. At the core of that, achieving high mobility in an ultrathin film is essential for the efficient operation of relevant electronic devices. While the state-of-the-art material systems, e.g., P(NDI2OD-T2) also known as N2200 can achieve high mobility in a thin film (typically > 20 nm), multitudinous challenges remain in processing an ultrathin film exhibiting desired charge transport morphology within a preferred thickness limit. Here, high electron mobility (a tenfold increase compared to annealed spin-coated films) is reported in both the top and bottom-gate configuration organic field-effect transistors comprising ultrathin N2200 films produced with a water-floating film transfer method. A range of characterization techniques are used to investigate these ultrathin films and their microstructure, and conclude that favorable edge-on polymer orientation at the top as well as throughout the ultrathin film thickness and the quality of π–π ordering as captured by the largest coherences length resulted in this high mobility in N2200 ultrathin films, in stark contrast to the commonly observed microstructural gradient in spin-coated thin films. The results provide new insight into the electronic and microstructural properties of thin films of organic semiconductors.}, journal={ADVANCED ELECTRONIC MATERIALS}, author={Steckmann, Thomas and Angunawela, Indunil and Kashani, Somayeh and Zhu, Youqin and Nahid, Masrur M. and Ade, Harald and Gadisa, Abay}, year={2022}, month={Mar} }
 @article{angunawela_nahid_ghasemi_amassian_ade_gadisa_2020, title={The Critical Role of Materials’ Interaction in Realizing Organic Field-Effect Transistors Via High-Dilution Blending with Insulating Polymers}, volume={12}, url={https://doi.org/10.1021/acsami.0c04208}, DOI={10.1021/acsami.0c04208}, abstractNote={High-performance low-band-gap polymer semiconductors are visibly colored, making them unsuitable for transparent and imperceptible electronics without reducing film thickness to the nanoscale range. Herein, we demonstrate polymer/insulator blends exhibiting favorable miscibility that improves the transparency and carrier transport in an organic field-effect transistor (OFET) device. The mesoscale structures leading to more efficient charge transport in ultrathin films relevant to the realization of transparent and flexible electronic applications are explored based on thermodynamic material interaction principles in conjunction with optical and morphological studies. By blending the commodity polymer polystyrene (PS) with two high-performing polymers, PDPP3T and P (NDI2OD-T2) (known as N2200), a drastic difference in morphology and fiber network are observed due to considerable differences in the degree of thermodynamic interaction between the conjugated polymers and PS. Intrinsic material interaction behavior establishes a long-range intermolecular interaction in the PDPP3T polymer fibrillar network dispersed in the majority (80%) PS matrix resulting in a ca. 3-fold increased transistor hole mobility of 1.15 cm2 V-1 s-1 (highest = 1.5 cm2 V-1 s-1) as compared to the pristine material, while PS barely affects the electron mobility in N2200. These basic findings provide important guidelines to achieve high mobility in transparent OFETs.}, number={23}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Angunawela, Indunil and Nahid, Masrur M. and Ghasemi, Masoud and Amassian, Aram and Ade, Harald and Gadisa, Abay}, year={2020}, month={Jun}, pages={26239–26249} }
 @article{angunawela_ye_bin_zhang_gadisa_li_ade_2019, title={Multi-length scale morphology of nonfullerene all-small molecule blends and its relation to device function in organic solar cells}, volume={3}, ISSN={["2052-1537"]}, url={https://doi.org/10.1039/C8QM00503F}, DOI={10.1039/C8QM00503F}, abstractNote={Device characteristics of a pair of nonfullerene small molecule solar cells were well correlated to their mesoscale morphology<italic>via</italic>resonant soft X-ray scattering.}, number={1}, journal={MATERIALS CHEMISTRY FRONTIERS}, publisher={Royal Society of Chemistry (RSC)}, author={Angunawela, Indunil and Ye, Long and Bin, Haijun and Zhang, Zhi-Guo and Gadisa, Abay and Li, Yongfang and Ade, Harald}, year={2019}, month={Jan}, pages={137–144} }
 @article{zhu_gadisa_peng_ghasemi_ye_xu_zhao_ade_2019, title={Rational Strategy to Stabilize an Unstable High-Efficiency Binary Nonfullerene Organic Solar Cells with a Third Component}, volume={9}, ISSN={["1614-6840"]}, url={http://dx.doi.org/10.1002/aenm.201900376}, DOI={10.1002/aenm.201900376}, abstractNote={Long device lifetime is still a missing key requirement in the commercialization of nonfullerene acceptor (NFA) organic solar cell technology. Understanding thermodynamic factors driving morphology degradation or stabilization is correspondingly lacking. In this report, thermodynamics is combined with morphology to elucidate the instability of highly efficient PTB7-Th:IEICO-4F binary solar cells and to rationally use PC71BM in ternary solar cells to reduce the loss in the power conversion efficiency from ≈35% to <10% after storage for 90 days and at the same time improve performance. The hypomiscibility observed for IEICO-4F in PTB7-Th (below the percolation threshold) leads to overpurification of the mixed domains. By contrast, the hypermiscibility of PC71BM in PTB7-Th of 48 vol% is well above the percolation threshold. At the same time, PC71BM is partly miscible in IEICO-4F suppressing crystallization of IEICO-4F. This work systematically illustrates the origin of the intrinsic degradation of PTB7-Th:IEICO-4F binary solar cells, demonstrates the structure–function relations among thermodynamics, morphology, and photovoltaic performance, and finally carries out a rational strategy to suppress the degradation: the third component needs to have a miscibility in the donor polymer at or above the percolation threshold, yet also needs to be partly miscible with the crystallizable acceptor.}, number={20}, journal={ADVANCED ENERGY MATERIALS}, publisher={Wiley}, author={Zhu, Youqin and Gadisa, Abay and Peng, Zhengxing and Ghasemi, Masoud and Ye, Long and Xu, Zheng and Zhao, Suling and Ade, Harald}, year={2019}, month={May} }
 @article{kim_schaefer_ma_zhao_turner_ghasemi_constantinou_so_yan_gadisa_et al._2019, title={The Critical Impact of Material and Process Compatibility on the Active Layer Morphology and Performance of Organic Ternary Solar Cells}, volume={9}, ISSN={["1614-6840"]}, url={https://doi.org/10.1002/aenm.201802293}, DOI={10.1002/aenm.201802293}, abstractNote={Although ternary solar cells (TSCs) offer a cost-effective prospect to expand the absorption bandwidth of organic solar cells, only few TSCs have succeeded in surpassing the performance of binary solar cells (BSCs) primarily due to the complicated morphology of the ternary blends. Here, the key factors that create and limit the morphology and performance of the TSCs are elucidated. The origin of morphology formation is explored and the role of kinetic factors is investigated. The results reveal that the morphology of TSC blends considered in this study are characterized with either a single length-scale or two length-scale features depending on the composition of the photoactive polymers in the blend. This asymmetric morphology development reveals that TSC blend morphology critically depends on material compatibility and polymer solubility. Most interestingly, the fill factor (FF) of TSCs is found to linearly correlate with the relative standard deviation of the fullerene distribution at small lengths. This is the first time that such a correlation has been shown for ternary systems. The criteria that uniform sized and highly pure amorphous domains are accomplished through the correct kinetic path to obtain a high FF for TSCs are specifically elucidated. The findings provide a critical insight for the precise design and processing of TSCs.}, number={2}, journal={ADVANCED ENERGY MATERIALS}, author={Kim, Joo-Hyun and Schaefer, Charley and Ma, Tingxuan and Zhao, Jingbo and Turner, Johnathan and Ghasemi, Masoud and Constantinou, Iordania and So, Franky and Yan, He and Gadisa, Abay and et al.}, year={2019}, month={Jan} }
 @article{xiong_ye_gadisa_zhang_rech_you_ade_2018, title={Revealing the Impact of F4-TCNQ as Additive on Morphology and Performance of High-Efficiency Nonfullerene Organic Solar Cells}, volume={29}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/ADFM.201806262}, DOI={10.1002/ADFM.201806262}, abstractNote={Fluorinated molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and its derivatives have been used in polymer:fullerene solar cells primarily as a dopant to optimize the electrical properties and device performance. However, the underlying mechanism and generality of how F4-TCNQ affects device operation and possibly the morphology is poorly understood, particularly for emerging nonfullerene organic solar cells. In this work, the influence of F4-TCNQ on the blend film morphology and photovoltaic performance of nonfullerene solar cells processed by a single halogen-free solvent is systematically investigated using a set of morphological and electrical characterizations. In solar cells with a high-performance polymer:small molecule blend FTAZ:IT-M, F4-TCNQ has a negligibly small effect on the molecular packing and surface characteristics, while it clearly affects the electronic properties and mean-square composition variation of the bulk. In comparison to the control devices with an average power conversion efficiency (PCE) of 11.8%, inclusion of a trace amount of F4-TCNQ in the active layer has improved device fill factor and current density, which has resulted into a PCE of 12.4%. Further increase in F4-TCNQ content degrades device performance. This investigation aims at delineating the precise role of F4-TCNQ in nonfullerene bulk heterojunction films, and thereby establishing a facile approach to fabricate highly optimized nonfullerene solar cells.}, number={1}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Xiong, Yuan and Ye, Long and Gadisa, Abay and Zhang, Qianqian and Rech, Jeromy James and You, Wei and Ade, Harald}, year={2018}, month={Nov}, pages={1806262} }
 @article{ghasemi_ye_zhang_yan_kim_awartani_you_gadisa_ade_2017, title={Panchromatic Sequentially Cast Ternary Polymer Solar Cells}, volume={29}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201604603}, DOI={10.1002/ADMA.201604603}, abstractNote={A sequential-casting ternary method is developed to create stratified bulk heterojunction (BHJ) solar cells, in which the two BHJ layers are spin cast sequentially without the need of adopting a middle electrode and orthogonal solvents. This method is found to be particularly useful for polymers that form a mechanically alloyed morphology due to the high degree of miscibility in the blend. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={4}, journal={Advanced Materials}, publisher={Wiley}, author={Ghasemi, Masoud and Ye, Long and Zhang, Qianqian and Yan, Liang and Kim, Joo-Hyun and Awartani, Omar and You, Wei and Gadisa, Abay and Ade, Harald}, year={2017}, month={Jan}, pages={1604603} }
 @article{ghasemi_ye_zhang_yan_kim_awartani_you_gadisa_ade_2017, title={Polymer Solar Cells: Panchromatic Sequentially Cast Ternary Polymer Solar Cells (Adv. Mater. 4/2017)}, volume={29}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201770022}, DOI={10.1002/ADMA.201770022}, number={4}, journal={Advanced Materials}, publisher={Wiley}, author={Ghasemi, Masoud and Ye, Long and Zhang, Qianqian and Yan, Liang and Kim, Joo-Hyun and Awartani, Omar and You, Wei and Gadisa, Abay and Ade, Harald}, year={2017}, month={Jan} }
 @article{ye_xiong_li_ghasemi_balar_turner_gadisa_hou_o’connor_ade_et al._2017, title={Precise Manipulation of Multilength Scale Morphology and Its Influence on Eco-Friendly Printed All-Polymer Solar Cells}, volume={27}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/ADFM.201702016}, DOI={10.1002/ADFM.201702016}, abstractNote={Significant efforts have lead to demonstrations of nonfullerene solar cells (NFSCs) with record power conversion efficiency up to ≈13% for polymer:small molecule blends and ≈9% for all-polymer blends. However, the control of morphology in NFSCs based on polymer blends is very challenging and a key obstacle to pushing this technology to eventual commercialization. The relations between phases at various length scales and photovoltaic parameters of all-polymer bulk-heterojunctions remain poorly understood and seldom explored. Here, precise control over a multilength scale morphology and photovoltaic performance are demonstrated by simply altering the concentration of a green solvent additive used in blade-coated films. Resonant soft X-ray scattering is used to elucidate the multiphasic morphology of these printed all-polymeric films and complements with the use of grazing incidence wide-angle X-ray scattering and in situ spectroscopic ellipsometry characterizations to correlate the morphology parameters at different length scales to the device performance metrics. Benefiting from the highest relative volume fraction of small domains, additive-free solar cells show the best device performance, strengthening the advantage of single benign solvent approach. This study also highlights the importance of high volume fraction of smallest domains in printed NFSCs and organic solar cells in general.}, number={33}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Ye, Long and Xiong, Yuan and Li, Sunsun and Ghasemi, Masoud and Balar, Nrup and Turner, Johnathan and Gadisa, Abay and Hou, Jianhui and O’Connor, Brendan T. and Ade, Harald and et al.}, year={2017}, month={Jul}, pages={1702016} }
 @article{kim_gadisa_schaefer_yao_gautam_balar_ghasemi_constantinou_so_o'connor_et al._2017, title={Strong polymer molecular weight-dependent material interactions: impact on the formation of the polymer/fullerene bulk heterojunction morphology}, volume={5}, ISSN={2050-7488 2050-7496}, url={http://dx.doi.org/10.1039/C7TA03052E}, DOI={10.1039/C7TA03052E}, abstractNote={The morphological evolution is initiated by L–L or L–S phase separation (left) and further developed by molecular mobility, governed by polymer–solvent interactions which determine the final domain size of the BHJ layer (right).}, number={25}, journal={Journal of Materials Chemistry A}, publisher={Royal Society of Chemistry (RSC)}, author={Kim, Joo-Hyun and Gadisa, Abay and Schaefer, Charley and Yao, Huifeng and Gautam, Bhoj R. and Balar, Nrup and Ghasemi, Masoud and Constantinou, Iordania and So, Franky and O'Connor, Brendan T. and et al.}, year={2017}, pages={13176–13188} }
 @article{hara_gadisa_fu_garvey_vrouwenvelder_miller_dempsey_lopez_2016, title={Gains and Losses in PbS Quantum Dot Solar Cells with Submicron Periodic Grating Structures}, volume={120}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/ACS.JPCC.6B01498}, DOI={10.1021/ACS.JPCC.6B01498}, abstractNote={Corrugated structures are integral to many types of photoelectronic devices, used essentially for the manipulation of optical energy inputs. Here, we have investigated the gains and losses incurred by this microscale geometrical change. We have employed nanostructured electrode gratings of 600 nm pitch in PbS colloidal quantum dot (PbS-CQD) solar cells and investigated their effect on photovoltaic properties. Solar cells employing grating structure achieved a 32% and 20% increase in short-circuit current density (Jsc) and power conversion efficiency, respectively, compared to nonstructured reference cells. The observed photocurrent increase of the structured devices mainly stems from the enhancement of photon absorption due to the trapping of optical energy by the grating structures. This optical absorption enhancement was particularly high in the near-infrared portion of the sun spectrum where PbS-based solar cells commonly present poor absorption. We have interestingly observed that the open-circuit vol...}, number={15}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Hara, Yukihiro and Gadisa, Abay and Fu, Yulan and Garvey, Timothy and Vrouwenvelder, Kristina T. and Miller, Christopher W. and Dempsey, Jillian L. and Lopez, Rene}, year={2016}, month={Apr}, pages={8005–8013} }
 @article{ye_xiong_yao_gadisa_zhang_li_ghasemi_balar_hunt_o’connor_et al._2016, title={High Performance Organic Solar Cells Processed by Blade Coating in Air from a Benign Food Additive Solution}, volume={28}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/ACS.CHEMMATER.6B03083}, DOI={10.1021/ACS.CHEMMATER.6B03083}, abstractNote={Solution processable conjugated organic materials have gained tremendous interest motivated by their potential of low cost, lightweight and especially easy manufacturing of large-area and flexible electronics. Toxic halogen-containing solvents have been widely used in the processing of organic electronics, particularly organic photovoltaics (OPVs). To transition this technology to more commercially attractive manufacturing approaches, removing these halogenated solvents remains one of the key challenges. Our morphological (hard/soft X-ray scattering) and calorimetric characterizations reveal that using o-methylanisole, a certified food additive, as processing solvent can achieve similar crystalline properties and domain spacing/purity with that achieved by widely used binary halogenated solvents (chlorobenzene and 1,8-diiodooctane), thus yielding comparable photovoltaic performance in spin-casted films. To move a step forward, we further present the potential of o-methylanisole as processing solvent in th...}, number={20}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Ye, Long and Xiong, Yuan and Yao, Huifeng and Gadisa, Abay and Zhang, Hao and Li, Sunsun and Ghasemi, Masoud and Balar, Nrup and Hunt, Adrian and O’Connor, Brendan T. and et al.}, year={2016}, month={Oct}, pages={7451–7458} }
 @article{turner_gadisa_2016, title={Role of Near Substrate and Bulk Polymer Morphology on Out-of-Plane Space-Charge Limited Hole Mobility}, volume={8}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/ACSAMI.6B11232}, DOI={10.1021/ACSAMI.6B11232}, abstractNote={Charge transport is a central issue in all types of organic electronic devices. In organic films, charge transport is crucially limited by film microstructure and the nature of the substrate/organic interface interactions. In this report, we discuss the influence of active layer thickness on space-charge limited hole transport in pristine polymer and polymer/fullerene bulk heterojunction thin films (∼15-300 nm) in a diode structure. According to the results, the out-of-plane hole mobility in pristine polymers is sensitive to the degree of polymer chain aggregation. Blending the polymers with a fullerene molecule does not change the trend of hole mobility if the polymer tends to make an amorphous structure. However, employing an aggregating polymer in a bulk heterojunction blend gives rise to a marked difference in charge carrier transport behavior compared to the pristine polymer and this difference is sensitive to active layer thickness. In aggregating polymer films, the thickness-dependent interchain interaction was found to have direct impact on hole mobility. The thickness-dependent mobility trend was found to correspond well with the trend of fill factors of corresponding bulk heterojunction solar cells. This investigation has a vital implication for material design and the development of efficient organic electronic devices, including solar cells and light-emitting diodes.}, number={48}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Turner, Johnathan and Gadisa, Abay}, year={2016}, month={Nov}, pages={33019–33024} }
 @article{gadisa_hara_fu_vrouwenvelder_dempsey_samulski_lopez_2015, title={Disparity in Optical Charge Generation and Recombination Processes in Upright and Inverted PbS Quantum-Dot Solar Cells}, volume={119}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/JP512305X}, DOI={10.1021/JP512305X}, abstractNote={The role of optical charge generation and nongeminate recombination on the photocurrent of upright and inverted colloidal-PbS quantum-dot solar cells is investigated. With a controlled active layer thickness, upright (PbS/fullerene) devices are found to present overall better photovoltaic performance relative to inverted devices, notwithstanding the better NIR photoconversion efficiency in the latter. Through detailed analysis and numerical optoelectronic simulations, we show that beyond incidental differences, these two device architectures have fundamentally dissimilar properties that stem from their particular optical generation characteristics and the nature of the recombination processes at play, with the inverted devices affected only by trap-assisted losses and the upright ones suffering from enhanced bimolecular recombination. This study unveils the role of device geometry and inherent material properties on the carrier generation and collection efficiency of the light-generated photocurrent in co...}, number={9}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Gadisa, Abay and Hara, Yukihiro and Fu, Yulan and Vrouwenvelder, Kristina T. and Dempsey, Jillian L. and Samulski, Edward T. and Lopez, Rene}, year={2015}, month={Feb}, pages={4606–4611} }
 @article{liu_kirsch_gadisa_aryal_mitran_samulski_lopez_2013, title={Effects of nano-patterned versus simple flat active layers in upright organic photovoltaic devices}, url={https://hdl.handle.net/11475/12338}, DOI={10.1088/0022-3727/46/2/024008}, abstractNote={Abstract A scalable procedure for nano-patterning the bulk heterojunction layer in organic photovoltaic (OPV) devices is reported. Nano-patterning is shown to increase light absorption in poly(3-hexylthiophene) : [6,6]-phenyl-C61-butyric acid methyl ester (P3HT : PCBM) devices (ITO\WO 3 \P3HT : PCBM\Ca\Al). Nano-patterning also modifies electric fields in OPV devices, thus affecting charge harvesting. Nano-patterned OPV devices with a power conversion efficiency of 4% are presented. Comparable efficiencies are also obtained by optimization of thicknesses in a flat-layer device. Trade-offs between absorption enhancement and charge harvesting deterioration induced by nano-patterning are discussed as well as possible optimization strategies.}, author={Liu, Yingchi and Kirsch, Christoph and Gadisa, Abay and Aryal, Mukti and Mitran, Sorin and Samulski, Edward T. and Lopez, Rene}, year={2013} }
 @article{tumbleston_gadisa_liu_collins_samulski_lopez_ade_2013, title={Modifications in Morphology Resulting from Nanoimprinting Bulk Heterojunction Blends for Light Trapping Organic Solar Cell Designs}, volume={5}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/AM402363R}, DOI={10.1021/AM402363R}, abstractNote={Nanoimprinting the photoactive layer of bulk heterojunction (BHJ) organic solar cells is a promising technique for enhancing device performance via improved light absorption. Here, we demonstrate that imprinting poly(3-hexylthiophene) (P3HT) and fullerene BHJ blends leads to adverse morphological changes within the photoactive nanopattern which have been previously overlooked. In particular, nanoimprinting induces a factor of 2 difference in polymer:fullerene composition between the nanopattern posts and interconnecting flash layer that inadvertently moves the composition outside the range for optimal performance. This occurs because of the strong tendency of regioregular P3HT to crystallize since imprinting blends based on amorphous regiorandom P3HT have uniform nanopattern composition. Based on these results, we outline promising design strategies, such as nanoimprinting amorphous polymers, to serve as guidelines for fabricating high-performance nanopatterned BHJ solar cells capable of maximized light absorption.}, number={16}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Tumbleston, John R. and Gadisa, Abay and Liu, Yingchi and Collins, Brian A. and Samulski, Edward T. and Lopez, Rene and Ade, Harald}, year={2013}, month={Aug}, pages={8225–8230} }
 @article{gadisa_hairfield_alibabaei_donley_samulski_lopez_2013, title={Solution Processed Al-Doped ZnO Nanoparticles/TiOx Composite for Highly Efficient Inverted Organic Solar Cells}, volume={5}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/AM401798G}, DOI={10.1021/AM401798G}, abstractNote={We investigated the electrical properties of solution processed Al-doped ZnO (AZO) nanoparticles, stabilized by mixing with a TiOx complex. Thin solid films cast from the solution of AZO-TiOx (AZOTi) (Ti/Zn ∼0.4 in the bulk and ∼0.8 on its surface) is processable in inert environment, without a need for either ambient air exposure for hydrolysis or high temperature thermal annealing commonly applied to buffer layers of most metal-oxides. It was found that the electronic structure of AZOTi matches the electronic structure of several electron acceptor and donor materials used in organic electronic devices, such as solar cells. Inverted solar cells employing a bulk heterojunction film of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester, cast on an indium–tin-oxide/AZOTi electrode, and capped with a tungsten oxide/aluminum back electrode, give rise to a nearly 70% fill factor and an optimized open-circuit voltage as a result of efficient hole blocking behavior of AZOTi. The resulting electron collecting/blocking capability of this material solves crucial interfacial recombination issues commonly observed at the organic/metal-oxide interface in most inverted organic bulk heterojunction solar cells.}, number={17}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Gadisa, Abay and Hairfield, Travis and Alibabaei, Leila and Donley, Carrie L. and Samulski, Edward T. and Lopez, Rene}, year={2013}, month={Aug}, pages={8440–8445} }
 @article{gadisa_liu_samulski_lopez_2012, title={Minimizing interfacial losses in inverted organic solar cells comprising Al-doped ZnO}, volume={100}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4729861}, DOI={10.1063/1.4729861}, abstractNote={We demonstrated a 35% enhancement in the efficiency of inverted solar cells as a result of increased open-circuit voltage and fill factor by adsorbing an ultrathin layer of a ruthenium dye N719 on an aluminum-doped zinc oxide (ZnO-Al) electron collecting interfacial layer. The interface modification with N719 changes the charge injection levels as indicated by ultraviolet photoemission spectroscopy. The efficiency of inverted solar cells comprising a bulk heterojunction photo-active film of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester has increased from ∼2.80% to 3.80% upon employing the dye modification of the electrode interface.}, number={25}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Gadisa, Abay and Liu, Yingchi and Samulski, Edward T. and Lopez, Rene}, year={2012}, month={Jun}, pages={253903} }
 @article{gadisa_liu_samulski_lopez_2012, title={Role of Thin n-Type Metal-Oxide Interlayers in Inverted Organic Solar Cells}, volume={4}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am300549v}, DOI={10.1021/am300549v}, abstractNote={We have investigated the photovoltaic properties of inverted solar cells comprising a bulk heterojunction film of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester, sandwiched between an indium–tin-oxide/Al-doped zinc oxide (ZnO-Al) front, and tungsten oxide/aluminum back electrodes. The inverted solar cells convert photons to electrons at an external quantum efficiency (EQE) exceeding 70%. This is a 10–15% increase over EQEs of conventional solar cells. The increase in EQE is not fully explained by the difference in the optical transparency of electrodes, interference effects due to an optical spacer effect of the metal-oxide electrode buffer layers, or variation in charge generation profile. We propose that a large additional splitting of excited states at the ZnO–Al/polymer interface leads to the considerably large photocurrent yield in inverted cells. Our finding provides new insights into the benefits of n-type metal-oxide interlayers in bulk heterojunction solar cells, namely the splitting of excited states and conduction of free electrons simultaneously.}, number={8}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Gadisa, Abay and Liu, Yingchi and Samulski, Edward T. and Lopez, Rene}, year={2012}, month={Jul}, pages={3846–3851} }
 @article{gadisa_tumbleston_ko_aryal_lopez_samulski_2012, title={The role of solvent and morphology on miscibility of methanofullerene and poly(3-hexylthiophene)}, volume={520}, ISSN={0040-6090}, url={http://dx.doi.org/10.1016/j.tsf.2012.03.117}, DOI={10.1016/j.tsf.2012.03.117}, abstractNote={A bicontinuous, percolating bulk heterojunction morphology is integral to organic polymer solar cells. Understanding the factors affecting the miscibility of photovoltaic polymers with a fullerene electron acceptor molecule is a key to controlling the morphology. Starting from discreet pure phases – a poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bilayer film – the evolution of the P3HT–PCBM interface was studied with particular attention to the role of residual solvent in P3HT on PCBM interdiffusion. This investigation shows that in the bilayer geometry PCBM can rapidly diffuse into amorphous P3HT, but phase separation is maintained if the P3HT layer is cast from a very volatile solvent or if it is annealed prior to casting the PCBM overlayer to complete the bilayer geometry.}, number={16}, journal={Thin Solid Films}, publisher={Elsevier BV}, author={Gadisa, Abay and Tumbleston, John R. and Ko, Doo-Hyun and Aryal, Mukti and Lopez, Rene and Samulski, Edward T.}, year={2012}, month={Jun}, pages={5466–5471} }
 @book{piersimoni_chambon_vandewal_mens_boonen_gadisa_izquierdo_filippone_ruttens_jan d'haen_et al._2011, title={Influence of Fullerene Ordering on the Energy of the Charge-Transfer State and Open-Circuit Voltage in Polymer:Fullerene Solar Cells}, url={http://hdl.handle.net/1942/12027}, author={PIERSIMONI, Fortunato and CHAMBON, Sylvain and VANDEWAL, Koen and MENS, Raoul and BOONEN, Tine and GADISA, Abay and Izquierdo, Marta and Filippone, Salvatore and RUTTENS, Bart and Jan D'HAEN and et al.}, year={2011} }
 @article{piersimoni_chambon_vandewal_mens_boonen_gadisa_izquierdo_filippone_ruttens_d'haen_et al._2011, title={Influence of fullerene ordering on the energy of the charge-transfer state and open-circuit voltage in polymer:fullerene solar cells}, url={https://hal.archives-ouvertes.fr/hal-00967322}, DOI={10.1021/jp110982m}, abstractNote={The influence of fullerene side chain functionalization on both the morphology and electro-optical properties of bulk-heterojunction polymer:fullerene solar cells is discussed through a systematic investigation of material blends consisting of the conjugated polymer poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) as donor and fullerene molecules with different side chains as the acceptor. The varying side chain of the fullerenes was found to induce morphological changes as confirmed by different analytical techniques such as Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), and Nuclear Magnetic Resonance (NMR). The fullerene with the shorter side chain, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), forms crystalline nanophases in the blend, while this is not the case for the alternative diphenylmethanofullerene acceptor, [6,6]-1,1-bis(4,4′-dodecyloxyphenyl)methanofullerene (DPM-12). The introduction of NMR allows us to estimate the fraction of crystalline fullerene. The morphological changes have a profound effect on the characteristics of charge transfer states (CT) formed at the polymer:fullerene interfaces. Crystallization of fullerene molecules shifts the energy of the CT state. This shift in energy is directly manifested in the open-circuit voltage of solar cells based on the fullerene acceptors under investigation.}, author={Piersimoni, Fortunato and Chambon, Sylvain and Vandewal, Koen and Mens, Raoul and Boonen, Tine and Gadisa, Abay and Izquierdo, Marta and Filippone, Salvatore and Ruttens, Bart and D'Haen, Jan and et al.}, year={2011} }
 @article{ko_tumbleston_gadisa_aryal_liu_lopez_samulski_2011, title={Light-trapping nano-structures in organic photovoltaic cells}, volume={21}, ISSN={0959-9428 1364-5501}, url={http://dx.doi.org/10.1039/c1jm12300a}, DOI={10.1039/c1jm12300a}, abstractNote={We review nano-structures used as light trapping schemes in organic photovoltaic (OPV) cells. Light management via nano-structures enables one to exploit sub-diffraction limit properties, thereby giving access to enhanced light absorption in OPV cells. Light trapping schemes have been demonstrated in the form of surface plasmons, anti-reflection coatings, and photonic crystal patterns. Versatile methods are now available to facilitate fabrication of such nano-structures on sufficiently large areas for OPV applications.}, number={41}, journal={Journal of Materials Chemistry}, publisher={Royal Society of Chemistry (RSC)}, author={Ko, Doo-Hyun and Tumbleston, John R. and Gadisa, Abay and Aryal, Mukti and Liu, Yingchi and Lopez, Rene and Samulski, Edward T.}, year={2011}, pages={16293–16303} }
 @article{thalluri_bolsée_gadisa_parchine_boonen_d'haen_boyukbayram_vandenbergh_cleij_lutsen_et al._2011, title={Opto-electrical and morphological characterization of water soluble conjugated polymers for eco-friendly hybrid solar cells}, volume={95}, ISSN={0927-0248}, url={http://dx.doi.org/10.1016/j.solmat.2011.07.010}, DOI={10.1016/j.solmat.2011.07.010}, abstractNote={Solid-state Dye-Sensitized Solar Cells (ss-DSSCs) are promising candidates for future low cost photovoltaic energy generation and are based on polymer/metal oxide donor/acceptor heterojunctions. However, a crucial drawback of hybrid solar cells is the use of environmental unfriendly solvents, such as toluene, chloroform, chlorobenzene, etc. in the phase of preparation. In this work towards eco-friendly processing, we use water as a solvent in the preparation of the photo-active layer for hybrid solar cells. We demonstrate eco-friendly hybrid polymer/titania solar cells consisting of water soluble polythiophene as light-absorber, donor and Hole Transporting Layer (HTL), above a TiO2 layer that acts as an acceptor and electron conductor. The water soluble conjugated polymer materials are studied in terms of their opto-electrical and morphological properties, leading to a better understanding of the resulting photovoltaic performance. An alternative new processing method in device preparation is introduced; yielding prototype solar cells with an efficiency of 0.7%. This promising solar cell device performance can be considered as a proof-of-principle for future eco-friendly solar cells.}, number={12}, journal={Solar Energy Materials and Solar Cells}, publisher={Elsevier BV}, author={Thalluri, Gopala Krishna V.V. and Bolsée, Jean-Christophe and Gadisa, Abay and Parchine, Mikhail and Boonen, Tine and D'Haen, Jan and Boyukbayram, Ayse E. and Vandenbergh, Joke and Cleij, Thomas J. and Lutsen, Laurence and et al.}, year={2011}, month={Dec}, pages={3262–3268} }
 @book{thalluri_bolsee_gadisa_parchine_boonen_jan d'haen_boyukbayram_vandenbergh_cleij_lutsen_et al._2011, title={Opto-electrical and morphological characterization of water soluble conjugated polymers for eco-friendly hybrid solar cells}, url={http://hdl.handle.net/1942/13011}, author={THALLURI, Krishna and BOLSEE, Jean-Christophe and Gadisa, Abay and PARCHINE, Mikhail and BOONEN, Tine and Jan D'HAEN and BOYUKBAYRAM, Ayse and VANDENBERGH, Joke and CLEIJ, Thomas and LUTSEN, Laurence and et al.}, year={2011} }
 @article{oosterbaan_bolsée_gadisa_vrindts_bertho_d'haen_cleij_lutsen_mcneill_thomsen_et al._2010, title={Alkyl-Chain-Length-Independent Hole Mobility via Morphological Control with Poly(3-alkylthiophene) Nanofibers}, volume={20}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.200901471}, DOI={10.1002/adfm.200901471}, abstractNote={The field-effect transistor (FET) and diode characteristics of poly(3-alkylthiophene) (P3AT) nanofiber layers deposited from nanofiber dispersions are presented and compared with those of layers deposited from molecularly dissolved polymer solutions in chlorobenzene. The P3AT n-alkyl-side-chain length was varied from 4 to 9 carbon atoms. The hole mobilities are correlated with the interface and bulk morphology of the layers as determined by UV–vis spectroscopy, transmission electron microscopy (TEM) with selected area electron diffraction (SAED), atomic force microscopy (AFM), and polarized carbon K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The latter technique reveals the average polymer orientation in the accumulation region of the FET at the interface with the SiO2 gate dielectric. The previously observed alkyl-chain-length-dependence of the FET mobility in P3AT films results from differences in molecular ordering and orientation at the dielectric/semiconductor interface, and it is concluded that side-chain length does not determine the intrinsic mobility of P3ATs, but rather the alkyl chain length of P3ATs influences FET diode mobility only through changes in interfacial bulk ordering in solution processed films.}, number={5}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Oosterbaan, Wibren D. and Bolsée, Jean-Christophe and Gadisa, Abay and Vrindts, Veerle and Bertho, Sabine and D'Haen, Jan and Cleij, Thomas J. and Lutsen, Laurence and McNeill, Christopher R. and Thomsen, Lars and et al.}, year={2010}, month={Mar}, pages={792–802} }
 @book{oosterbaan_bolsee_gadisa_vrindts_bertho_jan d'haen_cleij_lutsen_mcneill_thomsen_et al._2010, title={Alkyl-Chain-Length-Independent Hole Mobility via Morphological Control with Poly(3-alkylthiophene) Nanofibers}, url={http://hdl.handle.net/1942/10876}, author={OOSTERBAAN, Wibren and BOLSEE, Jean-Christophe and GADISA, Abay and VRINDTS, Veerle and BERTHO, Sabine and Jan D'HAEN and CLEIJ, Thomas and LUTSEN, Laurence and McNeill, Christopher R. and Thomsen, Lars and et al.}, year={2010} }
 @article{gadisa_tvingstedt_vandewal_zhang_manca_inganäs_2010, title={Bipolar Charge Transport in Fullerene Molecules in a Bilayer and Blend of Polyfluorene Copolymer and Fullerene}, volume={22}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.200902579}, DOI={10.1002/adma.200902579}, abstractNote={Efficient polymer solar cells typically contain the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which promotes dissociation of excited states and enhances charge transport. The ability of PCBM to transport holes in solar cell bulk heterojunction films is monitored via the electroluminescence emission of a bulk heterojunction blend of PCBM and a polyfluorene copolymer. In polymer/fullerene bilayer diodes, fullerene emission is also observed.}, number={9}, journal={Advanced Materials}, publisher={Wiley}, author={Gadisa, Abay and Tvingstedt, Kristofer and Vandewal, Koen and Zhang, Fengling and Manca, Jean V. and Inganäs, Olle}, year={2010}, pages={1008–1011} }
 @book{gadisa_tvingstedt_vandewal_zhang_manca_inganas_2010, title={Bipolar Charge Transport in Fullerene Molecules in a Bilayer and Blend of Polyfluorene Copolymer and Fullerene}, url={http://hdl.handle.net/1942/10807}, author={GADISA, Abay and Tvingstedt, Kristofer and VANDEWAL, Koen and Zhang, Fengling and MANCA, Jean and Inganas, Olle}, year={2010} }
 @article{vandewal_tvingstedt_gadisa_inganäs_manca_2010, title={Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells}, url={http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-54852}, DOI={10.1103/PhysRevB.81.125204}, abstractNote={The open-circuit voltage $({V}_{oc})$ of polymer:fullerene bulk heterojunction solar cells is determined by the interfacial charge-transfer (CT) states between polymer and fullerene. Fourier-transform photocurrent spectroscopy and electroluminescence spectra of several polymer:fullerene blends are used to extract the relevant interfacial molecular parameters. An analytical expression linking these properties to ${V}_{oc}$ is deduced and shown to be valid for photovoltaic devices comprising three commonly used conjugated polymers blended with the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). ${V}_{oc}$ is proportional to the energy of the CT states ${E}_{CT}$. The energetic loss $q\ensuremath{\Delta}V$ between ${E}_{CT}$ and $q{V}_{oc}$ vanishes when approaching 0 K. It depends linearly on $T$ and logarithmically on illumination intensity. Furthermore $q\ensuremath{\Delta}V$ can be reduced by decreasing the electronic coupling between polymer and fullerene or by reducing the nonradiative recombination rate. For the investigated devices we find a loss $q\ensuremath{\Delta}V$ of $\ensuremath{\sim}0.6\text{ }\text{eV}$ at room temperature and under solar illumination conditions, of which $\ensuremath{\sim}0.25\text{ }\text{eV}$ is due to radiative recombination via the CT state and $\ensuremath{\sim}0.35\text{ }\text{eV}$ is due to nonradiative recombination.}, author={Vandewal, Koen and Tvingstedt, Kristofer and Gadisa, Abay and Inganäs, Olle and Manca, Jean V}, year={2010} }
 @book{vandewal_tvingstedt_gadisa_inganas_manca_2010, title={Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells}, url={http://hdl.handle.net/1942/10882}, author={VANDEWAL, Koen and Tvingstedt, Kristofer and GADISA, Abay and Inganas, Olle and MANCA, Jean}, year={2010} }
 @article{gadisa_oosterbaan_vandewal_bolsée_bertho_d'haen_lutsen_vanderzande_manca_2009, title={Effect of Alkyl Side-Chain Length on Photovoltaic Properties of Poly(3-alkylthiophene)/PCBM Bulk Heterojunctions}, volume={19}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.200900797}, DOI={10.1002/adfm.200900797}, abstractNote={The morphological, bipolar charge-carrier transport, and photovoltaic characteristics of poly(3-alkylthiophene) (P3AT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends are studied as a function of alkyl side-chain length m, where m equals the number of alkyl carbon atoms. The P3ATs studied are poly(3-butylthiophene) (P3BT, m = 4), poly(3-pentylthiophene) (P3PT, m = 5), and poly(3-hexylthiophene) (P3HT, m = 6). Solar cells with these blends deliver similar order of photo-current yield (exceeding 10 mA cm−2) irrespective of side-chain length. Power conversion efficiencies of 3.2, 4.3, and 4.6% are within reach using solar cells with active layers of P3BT:PCBM (1:0.8), P3PT:PCBM (1:1), and P3HT:PCBM (1:1), respectively. A difference in fill factor values is found to be the main source of efficiency difference. Morphological studies reveal an increase in the degree of phase separation with increasing alkyl chain length. Moreover, while P3PT:PCBM and P3HT:PCBM films have similar hole mobility, measured by hole-only diodes, the hole mobility in P3BT:PCBM lowers by nearly a factor of four. Bipolar measurements made by field-effect transistor showed a decrease in the hole mobility and an increase in the electron mobility with increasing alkyl chain length. Balanced charge transport is only achieved in the P3HT:PCBM blend. This, together with better processing properties, explains the superior properties of P3HT as a solar cell material. P3PT is proved to be a potentially competitive material. The optoelectronic and charge transport properties observed in the different P3AT:PCBM bulk heterojunction (BHJ) blends provide useful information for understanding the physics of BHJ films and the working principles of the corresponding solar cells.}, number={20}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Gadisa, Abay and Oosterbaan, Wibren D. and Vandewal, Koen and Bolsée, Jean-Christophe and Bertho, Sabine and D'Haen, Jan and Lutsen, Laurence and Vanderzande, Dirk and Manca, Jean V.}, year={2009}, month={Oct}, pages={3300–3306} }
 @book{gadisa_oosterbaan_vandewal_bolsee_bertho_jan d'haen_lutsen_vanderzande_manca_2009, title={Effect of Alkyl Side-Chain Length on Photovoltaic Properties of Poly(3-alkylthiophene)/PCBM Bulk Heterojunctions}, url={http://hdl.handle.net/1942/10308}, author={GADISA, Abay and OOSTERBAAN, Wibren and VANDEWAL, Koen and BOLSEE, Jean-Christophe and BERTHO, Sabine and Jan D'HAEN and LUTSEN, Laurence and VANDERZANDE, Dirk and MANCA, Jean}, year={2009} }
 @article{tvingstedt_vandewal_gadisa_zhang_manca_inganäs olle_2009, title={Electroluminescence from Charge Transfer States in Polymer Solar Cells}, volume={131}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja903100p}, DOI={10.1021/ja903100p}, abstractNote={In this article we report the weak but omnipresent electroluminescence (EL) from several types of organic polymer:fullerene bulk heterojunction solar cells biased in the forward direction. The light emitted from blends of some commonly used polymers and the fullerene molecule is significantly different from that of any of the pure materials comprising the blend. The lower energy of the blend EL is found to correlate with both the voltage onset of emission and the open-circuit voltage of the photovoltaic cell under solar illumination. We accordingly interpret the emission to originate from interfacial charge transfer state recombination and emphasize EL as a very valuable tool to characterize the charge transfer state present in donor/acceptor organic photovoltaic (OPV) cells.}, number={33}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Tvingstedt, Kristofer and Vandewal, Koen and Gadisa, Abay and Zhang, Fengling and Manca, Jean and Inganäs Olle}, year={2009}, month={Aug}, pages={11819–11824} }
 @book{tvingstedt_vandewal_gadisa_zhang_manca_inganas_2009, title={Electroluminescence from Charge Transfer States in Polymer Solar Cells}, url={http://hdl.handle.net/1942/11482}, author={Tvingstedt, Kristofer and VANDEWAL, Koen and Gadisa, Abay and Zhang, Fengling and MANCA, Jean and Inganas, Olle}, year={2009} }
 @book{vandewal_tvingstedt_gadisa_inganas_manca_2009, title={On the origin of the open-circuit voltage of polymer-fullerene solar cells}, url={http://hdl.handle.net/1942/9992}, author={VANDEWAL, Koen and Tvingstedt, Kristofer and GADISA, Abay and Inganas, Olle and MANCA, Jean}, year={2009} }
 @article{vandewal_tvingstedt_gadisa_inganäs_manca_2009, title={On the origin of the open-circuit voltage of polymer–fullerene solar cells}, volume={8}, ISSN={1476-1122 1476-4660}, url={http://dx.doi.org/10.1038/nmat2548}, DOI={10.1038/nmat2548}, number={11}, journal={Nature Materials}, publisher={Springer Science and Business Media LLC}, author={Vandewal, Koen and Tvingstedt, Kristofer and Gadisa, Abay and Inganäs, Olle and Manca, Jean V.}, year={2009}, month={Oct}, pages={904–909} }
 @book{vanderzande_oosterbaan_vrindts_bertho_bolsee_gadisa_vandewal_manca_lutsen_cleij_et al._2009, title={The use of nanofibers of P3HT in bulk heterojunction solar cells: the effect of order and morphology on the performance of P3HT:PCBM blends}, url={http://hdl.handle.net/1942/10904}, author={VANDERZANDE, Dirk and OOSTERBAAN, Wibren and Vrindts, Veerle and BERTHO, Sabine and BOLSEE, Jean-Christophe and Gadisa, Abay and VANDEWAL, Koen and MANCA, Jean and LUTSEN, Laurence and CLEIJ, Thomas and et al.}, year={2009} }
 @article{vandewal_oosterbaan_bertho_vrindts_gadisa_lutsen_vanderzande_manca_2009, title={Varying polymer crystallinity in nanofiber poly(3-alkylthiophene): PCBM solar cells: Influence on charge-transfer state energy and open-circuit voltage}, volume={95}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3232242}, DOI={10.1063/1.3232242}, abstractNote={The effect of poly(3-alkylthiophene) (P3AT) crystallinity in (nanofiber P3AT):PCBM photovoltaic devices on the energy of the charge-transfer state (ECT) and on the open-circuit voltage (Voc) is investigated for poly(3-butythiophene), poly(3-pentylthiophene) and poly(3-hexylhiophene). P3AT crystallinity, expressed as the crystalline nanofiber mass fraction f to the total P3AT mass in the spin-coating dispersion, is varied between ∼0.1 and ∼0.9 by temperature control. ECT, as obtained by Fourier-transform photocurrent spectroscopy decreased with f as ECT=ECT0−0.2f eV. Alkyl side-chain length only influences ECT0. Voc relates to ECT as Voc=ECT/q−0.6 V.}, number={12}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Vandewal, Koen and Oosterbaan, Wibren D. and Bertho, Sabine and Vrindts, Veerle and Gadisa, Abay and Lutsen, Laurence and Vanderzande, Dirk and Manca, Jean V.}, year={2009}, month={Sep}, pages={123303} }
 @book{vandewal_oosterbaan_bertho_vrindts_gadisa_lutsen_vanderzande_manca_2009, title={Varying polymer crystallinity in nanofiber poly(3-alkylthiophene): PCBM solar cells: Influence on charge-transfer state energy and open-circuit voltage}, url={http://hdl.handle.net/1942/9991}, author={VANDEWAL, Koen and OOSTERBAAN, Wibren and BERTHO, Sabine and VRINDTS, Veerle and GADISA, Abay and LUTSEN, Laurence and VANDERZANDE, Dirk and MANCA, Jean}, year={2009} }
 @book{bertho_janssen_cleij_conings_moons_gadisa dinku_jan d'haen_goovaerts_lutsen_manca_et al._2008, title={Effect of temperature on the morphological and photovoltaic stability of bulk heterojunction polymer: fullerene solar cells}, url={http://hdl.handle.net/1942/8330}, author={BERTHO, Sabine and Janssen, Griet and CLEIJ, Thomas and CONINGS, Bert and MOONS, Wouter and GADISA DINKU, Abay and Jan D'HAEN and Goovaerts, E. and LUTSEN, Laurence and MANCA, Jean and et al.}, year={2008} }
 @article{haeldermans_vandewal_oosterbaan_gadisa_d’haen_van bael_manca_mullens_2008, title={Ground-state charge-transfer complex formation in hybrid poly(3-hexyl thiophene):titanium dioxide solar cells}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3041633}, DOI={10.1063/1.3041633}, abstractNote={The existence of a ground-state charge-transfer (CT) complex in a conjugated polymer:metal oxide nanoparticle bulk heterojunction photovoltaic cell is demonstrated by Fourier-transform photocurrent spectroscopy (FTPS). The CT complex between poly(3-hexylthiophene) (P3HT) and titanium dioxide (TiO2) is characterized by a weak additional photocurrent band (onset 1eV) in the FTPS spectra, situated below the conjugated polymer bandgap of 2eV. The presence of CT interaction between P3HT and TiO2 in relation to frontier orbital alignment is discussed, as well as the contribution of a sub-bandgap interfacial CT state to the electron transfer process in P3HT:TiO2 solar cells.}, number={22}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Haeldermans, I. and Vandewal, K. and Oosterbaan, W. D. and Gadisa, A. and D’Haen, J. and Van Bael, M. K. and Manca, J. V. and Mullens, J.}, year={2008}, month={Dec}, pages={223302} }
 @book{haeldermans_vandewal_oosterbaan_gadisa dinku_jan d'haen_van bael_manca_mullens_2008, title={Ground-state charge-transfer complex formation in hybrid poly(3-hexyl thiophene):titanium dioxide solar cells}, url={http://hdl.handle.net/1942/9087}, author={HAELDERMANS, Ilse and VANDEWAL, Koen and OOSTERBAAN, Wibren and GADISA DINKU, Abay and Jan D'HAEN and VAN BAEL, Marlies and MANCA, Jean and MULLENS, Jules}, year={2008} }
 @article{vandewal_gadisa_oosterbaan_bertho_banishoeib_van severen_lutsen_cleij_vanderzande_manca_2008, title={The Relation Between Open-Circuit Voltage and the Onset of Photocurrent Generation by Charge-Transfer Absorption in Polymer : Fullerene Bulk Heterojunction Solar Cells}, volume={18}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/adfm.200800056}, DOI={10.1002/adfm.200800056}, abstractNote={Photocurrent generation by charge-transfer (CT) absorption is detected in a range of conjugated polymer–[6,6]-phenyl C61 butyric acid methyl ester (PCBM) based solar cells. The low intensity CT absorption bands are observed using a highly sensitive measurement of the external quantum efficiency (EQE) spectrum by means of Fourier-transform photocurrent spectroscopy (FTPS). The presence of these CT bands implies the formation of weak ground-state charge-transfer complexes in the studied polymer–fullerene blends. The effective band gap (Eg) of the material blends used in these photovoltaic devices is determined from the energetic onset of the photocurrent generated by CT absorption. It is shown that for all devices, under various preparation conditions, the open-circuit voltage (Voc) scales linearly with Eg. The redshift of the CT band upon thermal annealing of regioregular poly(3-hexylthiophene):PCBM and thermal aging of poly(phenylenevinylene)(PPV):PCBM photovoltaic devices correlates with the observed drop in open-circuit voltage of high-temperature treated versus untreated devices. Increasing the weight fraction of PCBM also results in a redshift of Eg, proportional with the observed changes in Voc for different PPV:PCBM ratios. As Eg corresponds with the effective bandgap of the material blends, a measurement of the EQE spectrum by FTPS allows us to measure this energy directly on photovoltaic devices, and makes it a valuable technique in the study of organic bulk heterojunction solar cells.}, number={14}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Vandewal, Koen and Gadisa, Abay and Oosterbaan, Wibren D. and Bertho, Sabine and Banishoeib, Fateme and Van Severen, Ineke and Lutsen, Laurence and Cleij, Thomas J. and Vanderzande, Dirk and Manca, Jean V.}, year={2008}, month={Jul}, pages={2064–2070} }
 @book{vandewal_gadisa dinku_oosterbaan_bertho_banishoeib_van severen_lutsen_cleij_vanderzande_manca_2008, title={The relation between open-circuit voltage and the onset of photocurrent generation by charge-transfer absorption in polymer: Fullerene bulk heterojunction solar cells}, url={http://hdl.handle.net/1942/8450}, author={VANDEWAL, Koen and GADISA DINKU, Abay and OOSTERBAAN, Wibren and BERTHO, Sabine and BANISHOEIB, Fateme and VAN SEVEREN, Ineke and LUTSEN, Laurence and CLEIJ, Thomas and VANDERZANDE, Dirk and MANCA, Jean}, year={2008} }
 @article{gadisa_mammo_andersson_admassie_zhang_andersson_inganäs_2007, title={A New Donor–Acceptor–Donor Polyfluorene Copolymer with Balanced Electron and Hole Mobility}, volume={17}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.200700441}, DOI={10.1002/adfm.200700441}, abstractNote={A new alternating polyfluorene copolymer poly[2,7-(9,9-dioctylfluoren)-alt-5,5-(5′,8′-di-2-thienyl-(2′,3′-bis-(3′′-octyloxyphenyl)-quinoxaline))] (APFO-15), which has electron donor–acceptor–donor units in between the fluorene units, is synthesized and characterized. This polymer has a strong absorption and emission in the visible range of the solar spectrum. Its electroluminescence and photoluminescence emissions extend from about 560 to 900 nm. Moreover, solar cells with efficiencies in excess of 3.5 % have been realized from blends of APFO-15 and an electron acceptor molecule, a methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). It has also been observed that electron and hole transport is balanced both in the pure polymer phase and in polymer/PCBM bulk heterojunction films, which makes this material quite attractive for applications in opto-electronic devices.}, number={18}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Gadisa, A. and Mammo, W. and Andersson, L.  M. and Admassie, S. and Zhang, F. and Andersson, M. R. and Inganäs, O.}, year={2007}, month={Dec}, pages={3836–3842} }
 @article{gadisa_zhang_sharma_svensson_andersson_inganäs_2007, title={Improvements of fill factor in solar cells based on blends of polyfluorene copolymers as electron donors}, volume={515}, ISSN={0040-6090}, url={http://dx.doi.org/10.1016/j.tsf.2006.08.043}, DOI={10.1016/j.tsf.2006.08.043}, abstractNote={The photovoltaic characteristics of solar cells based on alternating polyfluorene copolymers, poly(2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (APFO-3), and poly(2,7-(9,9-didodecyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (APFO-4), blended with an electron acceptor fullerene molecule [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), have been investigated and compared. The two copolymers have the same aromatic backbone structure but differ by the length of their alkyl side chain. The overall photovoltaic performance of the solar cells is comparable irrespective of the copolymer used in the active layer. However, the fill factor (FF) values of the devices are strongly affected by the copolymer type. Higher FF values were realized in solar cells with APFO-4 (with longer alkyl side chain)/PCBM bulk heterojunction active layer. On the other hand, devices with blends of APFO-3/APFO-4/PCBM were found to render fill factor values that are intermediate between the values obtained in solar cells with APFO-3/PCBM and APFO-4/PCBM active film. Upon using APFO-3/APFO-4 blends as electron donors, the cell efficiency can be enhanced by about 16% as compared to cells with either APFO-3 or APFO-4. The transport of holes in each polymer obeys the model of hopping transport in disordered media. However, the degree of energetic barrier against hopping was found to be larger in APFO-3. The tuning of the photovoltaic parameters will be discussed based on studies of hole transport in the pure polymer films, and morphology of blend layers. The effect of bipolar transport in PCBM will also be discussed.}, number={5}, journal={Thin Solid Films}, publisher={Elsevier BV}, author={Gadisa, Abay and Zhang, Fengling and Sharma, Deepak and Svensson, Mattias and Andersson, Mats R. and Inganäs, Olle}, year={2007}, month={Jan}, pages={3126–3131} }
 @article{mammo_admassie_gadisa_zhang_inganas_andersson_2007, title={New low band gap alternating polyfluorene copolymer-based photovoltaic cells}, volume={91}, ISSN={0927-0248}, url={http://dx.doi.org/10.1016/j.solmat.2007.02.018}, DOI={10.1016/j.solmat.2007.02.018}, abstractNote={New low band gap alternating polyfluorene copolymers were synthesized for use in plastic solar cells and their optical, electrochemical, and photovoltaic characteristics were determined. These polymers incorporated fluorene units alternating with groups including electron-withdrawing (A) and electron-donating (D) groups in donor–acceptor–donor (DAD) sequence to achieve the lowering of band gaps. The HOMO–LUMO values were estimated from electrochemical studies. By varying the donor and acceptor strength and position of the solubilizing substituents, similar HOMO values were obtained. These values were also found to correlate well with the open circuit voltage (VOC) values determined from photovoltaic data of the polymers blended with the acceptor PCBM. Despite similar HOMO values, the absorption spectra of the polymers differ significantly. This prompted the preparation of photovoltaic devices consisting of blends of two polymers with complementary absorptions in combination with PCBM to harvest more photons in the polymer solar cells.}, number={11}, journal={Solar Energy Materials and Solar Cells}, publisher={Elsevier BV}, author={Mammo, W and Admassie, S and Gadisa, A and Zhang, F and Inganas, O and Andersson, M}, year={2007}, month={Jul}, pages={1010–1018} }
 @article{gadisa_perzon_andersson_inganäs_2007, title={Red and near infrared polarized light emissions from polyfluorene copolymer based light emitting diodes}, volume={90}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2713139}, DOI={10.1063/1.2713139}, abstractNote={The authors report polarized red, electroluminescence peak at 705nm and near infrared, electroluminescence peak at 950nm, light emission from light emitting diodes based on two polyfluorene copolymers. The copolymers are synthesized from a fluorene monomer combined with donor-acceptor-donor comonomers and designed to have a low band gap and form birefringent liquid crystalline phases. Emission occurs from aligned thin films of polymer layers. The emissive layers are aligned by spin coating on a layer of rubbed conducting polymer poly(3,4-ethylene dioxythiophene)-poly(styrene sulphonate) and thermally converted into glassy nematic liquid crystalline state.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Gadisa, Abay and Perzon, Erik and Andersson, Mats R. and Inganäs, Olle}, year={2007}, month={Mar}, pages={113510} }
 @article{jespersen_zhang_gadisa_sundström_yartsev_inganäs_2006, title={Charge formation and transport in bulk-heterojunction solar cells based on alternating polyfluorene copolymers blended with fullerenes}, volume={7}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2006.03.001}, DOI={10.1016/j.orgel.2006.03.001}, abstractNote={We investigate charge formation in bulk-heterojunction solar cells based on conjugated polymers in the form of alternating polyfluorene copolymers and the methanofullerene PCBM. Using transient absorption spectroscopy we show that optimal charge formation is obtained with 20–50 wt% PCBM. This is in contrast to the maximum short circuit current density obtained at ∼80 wt% PCBM as determined by steady state current density–voltage characterization. Hence, we show explicitly that the solar cell performance of these interpenetrating polymer networks containing PCBM is limited by charge transport rather than by formation of charges.}, number={4}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Jespersen, Kim G. and Zhang, Fengling and Gadisa, Abay and Sundström, Villy and Yartsev, Arkady and Inganäs, Olle}, year={2006}, month={Aug}, pages={235–242} }
 @article{gadisa_wang_admassie_perzon_oswald_langa_andersson_inganäs_2006, title={Stoichiometry dependence of charge transport in polymer/methanofullerene and polymer/C70 derivative based solar cells}, volume={7}, ISSN={1566-1199}, url={http://dx.doi.org/10.1016/j.orgel.2006.01.003}, DOI={10.1016/j.orgel.2006.01.003}, abstractNote={Charge transport in a near infrared absorbing polyfluorene copolymer (APFO-Green1) and its blends with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and 3′-(3,5-bis-trifluoromethylphenyl)-1′-(4-nitrophenyl)pyrazolino[70]fullerene (BTPF70) is reported. PCBM and BTPF70 are electron acceptor and transporting molecules in polymer based solar cells. The BTPF70 has emerged as a new electron acceptor molecule that provides adequate exciton dissociation when blended with the low band gap polyfluorene copolymer APFO-Green1. Electron transport in both net PCBM and BTPF70 films are subjected to positional and energetic disorder, with the degree of disorder being more pronounced in BTPF70. On the other hand, mixing PCBM with conjugated polymers usually leads to increased hole mobility. We have investigated and compared the acceptor concentration dependence of charge transport in APFO-Green1/PCBM and APFO-Green1/BTPF70 blend films. For better understanding of the charge transport in the heterojunction films, the field and temperature dependence of hole transport in pure APFO-Green1 films has also been studied. It is observed that the behavior of hole mobility in the blend layer is sensitive to the acceptor type. For APFO-Green1/PCBM hole only devices, the hole mobility attains a local maximum at 67 wt.% of PCBM, while on the contrary mixing any amount of BTPF70 with APFO-Green1 results into degradation of hole transport. Electron transport in both blends, however, increases monotonically as a function of acceptor loading.}, number={4}, journal={Organic Electronics}, publisher={Elsevier BV}, author={Gadisa, Abay and Wang, Xiangjun and Admassie, Shimelis and Perzon, Erik and Oswald, Frédéric and Langa, Fernando and Andersson, Mats R. and Inganäs, Olle}, year={2006}, month={Aug}, pages={195–204} }
 @phdthesis{gadisa_2006, title={Studies of Charge Transport and Energy Level in Solar Cells Based on Polymer/Fullerene Bulk Heterojunction}, url={http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8047}, author={Gadisa, Abay}, year={2006} }
 @article{gadisa_tvingstedt_admassie_lindell_crispin_andersson_salaneck_inganäs_2006, title={Transparent polymer cathode for organic photovoltaic devices}, volume={156}, ISSN={0379-6779}, url={http://dx.doi.org/10.1016/j.synthmet.2006.07.006}, DOI={10.1016/j.synthmet.2006.07.006}, abstractNote={We demonstrate a prototype solar cell with a transparent polymer cathode, and indium-tin-oxide (ITO)/poly (3, 4-ethylene dioxythiophene)-poly (styrene sulphonate) (PEDOT:PSS) anode. As an active layer, thin film of a bulk heterojunction of polyfluorene copolymer poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2thienyl-2′,1′3′-benzothiadiazole)] (APFO-3) and an electron acceptor molecule [6], [6]-phenyl-C61-butyric acid methyl ester (PCBM) (1:4 wt.) was sandwiched between the two transparent polymer electrodes. The cathode is another form of PEDOT formed by vapor phase polymerised PEDOT (VPP PEDOT) of conductivity 102–103 S/cm. The cathode is supported on an elastomeric substrate, and forms a conformal contact to the APFO-3/PCBM blend. Transparent solar cells are useful for building multilayer and tandem solar cells.}, number={16-17}, journal={Synthetic Metals}, publisher={Elsevier BV}, author={Gadisa, Abay and Tvingstedt, Kristofer and Admassie, Shimelis and Lindell, L. and Crispin, X. and Andersson, Mats R. and Salaneck, W.R. and Inganäs, Olle}, year={2006}, month={Aug}, pages={1102–1107} }
 @article{gadisa_svensson_andersson_inganäs_2004, title={Correlation between oxidation potential and open-circuit voltage of composite solar cells based on blends of polythiophenes/ fullerene derivative}, volume={84}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1650878}, DOI={10.1063/1.1650878}, abstractNote={The photovoltaic parameters of donor/acceptor blend organic solar cells are highly influenced by several parameters, such as the strength of the acceptor species, the morphology of the film due to the solvent, and the mobility of the free charge carriers. In this work, the open-circuit voltage (Voc) of solar cells based on series of conjugated polythiophene polymers were measured and compared. In every cell, the donor polymer was blended with an electron acceptor fullerene molecule. The devices were constructed in a sandwich structure with indium tin oxide (ITO)/metallic polymer (PEDOT:PSS) acting as an anode and Al or LiF/Al acting as a cathode. Comparing the Voc of all the cells shows that this important photovoltaic parameter is systematically varying with the polymer. The variation of photovoltage is attributed to the variation of the oxidation potential of the donor conjugated polymers after due consideration of the different injection conditions in the varying polymers.}, number={9}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Gadisa, Abay and Svensson, Mattias and Andersson, Mats R. and Inganäs, Olle}, year={2004}, month={Mar}, pages={1609–1611} }
 @article{zhang_gadisa_inganäs_svensson_andersson_2004, title={Influence of buffer layers on the performance of polymer solar cells}, volume={84}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1739279}, DOI={10.1063/1.1739279}, abstractNote={The influence of different anode buffer layers on the performance of solar cells based on blends of polyfluorene copolymer poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (DiO-PFDTBT), acting as electron donor, and [6,6]-phenyl-C61-butyric acid methylester (PCBM), acting as electron acceptor was studied. The buffer layers were constructed from different forms of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)(PEDOT-PSS). Variations in open-circuit voltage, short-circuit current, and fill factor were observed. These were attributed to the slight rearrangement of the insulating layer PSS on top of PEDOT, which altered the charge injection at the interface between anode and photoactive layer.}, number={19}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Zhang, F. L. and Gadisa, A. and Inganäs, O. and Svensson, M. and Andersson, M. R.}, year={2004}, month={May}, pages={3906–3908} }
 @article{inganäs_svensson_zhang_gadisa_persson_wang_andersson_2004, title={Low bandgap alternating polyfluorene copolymers in plastic photodiodes and solar cells}, volume={79}, ISSN={0947-8396 1432-0630}, url={http://dx.doi.org/10.1007/S00339-003-2498-5}, DOI={10.1007/S00339-003-2498-5}, number={1}, journal={Applied Physics A}, publisher={Springer Science and Business Media LLC}, author={Inganäs, O. and Svensson, M. and Zhang, F. and Gadisa, A. and Persson, N.K. and Wang, X. and Andersson, M.R.}, year={2004}, month={Jun}, pages={31–35} }
 @article{bertho_janssen_cleij_conings_moons_gadisa_haen_goovaerts_lutsen_manca_et al., title={Effect of temperature on the morphological and photovoltaic stability of bulk heterojunction polymer:fullerene solar cells}, url={http://hdl.handle.net/10067/692900151162165141}, DOI={10.1016/J.SOLMAT.2008.01.006}, abstractNote={In high performance polymer:fullerene bulk heterojunction solar cells the nanoscale morphology of interpenetrating acceptor:donor materials is optimized through appropriate preparation conditions such as annealing and choice of solvent, but this initial state-of-the-art morphology will not remain stable during long-term operation. We report the effects of prolonged storage at elevated temperatures on both the morphology and the photovoltaic performance for the model systems MDMO-PPV:PCBM and P3HT:PCBM as compared to ‘High Tg PPV’:PCBM based solar cells, where the ‘High Tg PPV’ is characterized by its high glass transition temperature (138 °C). In situ monitoring of the photocurrent–voltage characteristics at elevated temperatures, in combination with a systematic transmission electron microscopy (TEM) study and complementary optical spectroscopy, reveals distinct degradation kinetics and morphological changes that indicate the occurrence of different underlying physico-chemical mechanisms.}, author={Bertho, Sabine and Janssen, Griet and Cleij, Thomas J. and Conings, Bert and Moons, Wouter and Gadisa, Abay and Haen, d' and Goovaerts, Etienne and Lutsen, Laurence and Manca, Jean and et al.} }
 @article{gadisa_zhang_sharma_svensson_andersson_inganas, title={Improvements of fill factor in solar cells based on blends of polyfluorene copolymers as electron donors}, url={http://itupl-ura1.ml.unisa.edu.au:80/R/?func=dbin-jump-full&object_id=116385}, author={Gadisa, Abay and Zhang, Fengling and Sharma, Deepak and Svensson, Mattias and Andersson, Mats and Inganas, Olle} }
 @article{mammo_admassie_gadisa, title={New low band gap alternating polyfluorene copolymer-based photovoltaic cells}, url={http://itupl-ura1.ml.unisa.edu.au:80/R/?func=dbin-jump-full&object_id=116388}, author={Mammo, Wendimagegn and Admassie, Shimelis and Gadisa, Abay} }
 @article{gadisa_perzon_andersson_inganas, title={Red and near infrared polarized light emissions from polyfluorene copolymer based light emitting diodes}, url={http://itupl-ura1.ml.unisa.edu.au:80/R/?func=dbin-jump-full&object_id=116386}, author={Gadisa, Abay and Perzon, Erik and Andersson, Mats and Inganas, Olle} }