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Crystallography, Morphology, Electronic Structure, and Transport in non-Fullerene/non-Indacenodithienothiophene Polymer:Y6 Solar Cells
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2020-07-23 , DOI: 10.1021/jacs.0c05560 Weigang Zhu , Austin P Spencer , Subhrangsu Mukherjee 1 , Joaquin M Alzola , Vinod K Sangwan , Samuel H Amsterdam , Steven M Swick , Leighton O Jones , Michael C Heiber 1 , Andrew A Herzing 1 , Guoping Li , Charlotte L Stern , Dean M DeLongchamp 1 , Kevin L Kohlstedt , Mark C Hersam , George C Schatz , Michael R Wasielewski , Lin X Chen 2 , Antonio Facchetti 3 , Tobin J Marks
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2020-07-23 , DOI: 10.1021/jacs.0c05560 Weigang Zhu , Austin P Spencer , Subhrangsu Mukherjee 1 , Joaquin M Alzola , Vinod K Sangwan , Samuel H Amsterdam , Steven M Swick , Leighton O Jones , Michael C Heiber 1 , Andrew A Herzing 1 , Guoping Li , Charlotte L Stern , Dean M DeLongchamp 1 , Kevin L Kohlstedt , Mark C Hersam , George C Schatz , Michael R Wasielewski , Lin X Chen 2 , Antonio Facchetti 3 , Tobin J Marks
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Emerging non-fullerene acceptors (NFAs) with crystalline domains enable high-performance bulk heterojunction (BHJ) solar cells. Thermal annealing is known to enhance BHJ photoactive layer morphology and performance. However, the microscopic mechanism of annealing-induced performance enhancement is poorly understood in emerging NFAs, espe-cially regarding competing factors. Here, optimized thermal annealing of the model system PBDB-TF:Y6 (Y6 = 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2",3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]-thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) decreases open circuit voltage (VOC) but increases the short circuit current (JSC) and fill factor (FF) such that the resulting power conversion efficiency (PCE) increases from 14% to 15% in ambient. Here we systematically investigate these thermal annealing effects through in-depth characteri-zations of carrier mobility, film morphology, charge photogeneration and recombination, using SCLC, GIXRD, AFM, XPS, NEXAFS, R-SoXS, TEM, STEM, fs/ns TA spectroscopy, 2DES, and impedance spectroscopy. Surprisingly, thermal annealing does not alter film crystallinity, nor R-SoXS characteristic size scale, relative average phase purity, nor TEM-imaged phase separation, but rather facilitates Y6 migration to the BHJ film top surface, changes the PBDB-TF/Y6 vertical phase separa-tion and intermixing, and reduces bottom surface roughness. While these morphology changes increase bimolecular re-combination (BR) and lower the free charge (FC) yield, they also increase the average of electron and hole mobility by at least two-fold. Importantly, the increased μh dominates and underlies the increased FF and PCE. Single-crystal X-ray diffraction reveals that Y6 molecules co-facially pack via their end-groups/cores, with the shortest π-π distance as close as 3.34 Å, clarifying out-of-plane π-face-on molecular orientation in the nano-crystalline BHJ domains. DFT analysis of Y6 crystals reveals hole/electron re-organization energies as low as 160/150 meV, large intermolecular electronic coupling integrals of 12.1 - 37.9 meV, ra-tionalizing the 3D electron transport and relatively high μe of 10-4 cm2 V-1 s-1. Taken all together, this work clarifies the richness of thermal annealing effects in high-efficiency NFA solar cells and tasks for future materials design.
中文翻译：
非富勒烯/非茚二噻吩聚合物的晶体学、形态学、电子结构和传输：Y6 太阳能电池
具有结晶域的新兴非富勒烯受体 (NFA) 使高性能体异质结 (BHJ) 太阳能电池成为可能。已知热退火可增强 BHJ 光敏层形态和性能。然而，退火引起的性能增强的微观机制在新兴的 NFA 中知之甚少，尤其是在竞争因素方面。这里，模型系统 PBDB-TF:Y6 (Y6 = 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl)- 12,13-二氢-[1,2,5]噻二唑并[3,4-e]噻吩并[2",3'':4',5']噻吩并[2',3':4,5]吡咯并[ 3,2-g]噻吩并[2',3':4,5]-噻吩并[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3- oxo-2,3-dihydro-1H-indene-2, 1-diylidene))dimalononitrile) 降低开路电压 (VOC)，但增加短路电流 (JSC) 和填充因子 (FF)，因此在环境中产生的功率转换效率 (PCE) 从 14% 增加到 15%。在这里，我们使用 SCLC、GIXRD、AFM、XPS、NEXAFS、R-SoXS、TEM、STEM、fs/ns TA，通过载流子迁移率、薄膜形态、电荷光生和复合的深入表征，系统地研究了这些热退火效应谱、2DES 和阻抗谱。令人惊讶的是，热退火不会改变薄膜结晶度、R-SoXS 特征尺寸尺度、相对平均相纯度或 TEM 成像相分离，而是促进 Y6 迁移到 BHJ 薄膜顶面，改变 PBDB-TF/Y6 垂直相分离和混合，并降低底面粗糙度。虽然这些形态变化增加了双分子重组 (BR) 并降低了自由电荷 (FC) 产率，但它们也将电子和空穴迁移率的平均值增加了至少两倍。重要的是，增加的 μh 在增加的 FF 和 PCE 中占主导地位并成为其基础。单晶 X 射线衍射显示 Y6 分子通过其端基/核共面堆积，最短 π-π 距离接近 3.34 Å，阐明了面外 π-face-on 分子取向纳米晶体 BHJ 域。Y6 晶体的 DFT 分析显示空穴/电子重组能低至 160/150 meV，12.1 - 37.9 meV 的大分子间电子耦合积分，合理化 3D 电子传输和相对较高的 10-4 cm2 V- 1 秒-1。综合起来，
更新日期：2020-07-23
中文翻译：
非富勒烯/非茚二噻吩聚合物的晶体学、形态学、电子结构和传输：Y6 太阳能电池
具有结晶域的新兴非富勒烯受体 (NFA) 使高性能体异质结 (BHJ) 太阳能电池成为可能。已知热退火可增强 BHJ 光敏层形态和性能。然而，退火引起的性能增强的微观机制在新兴的 NFA 中知之甚少，尤其是在竞争因素方面。这里，模型系统 PBDB-TF:Y6 (Y6 = 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl)- 12,13-二氢-[1,2,5]噻二唑并[3,4-e]噻吩并[2",3'':4',5']噻吩并[2',3':4,5]吡咯并[ 3,2-g]噻吩并[2',3':4,5]-噻吩并[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3- oxo-2,3-dihydro-1H-indene-2, 1-diylidene))dimalononitrile) 降低开路电压 (VOC)，但增加短路电流 (JSC) 和填充因子 (FF)，因此在环境中产生的功率转换效率 (PCE) 从 14% 增加到 15%。在这里，我们使用 SCLC、GIXRD、AFM、XPS、NEXAFS、R-SoXS、TEM、STEM、fs/ns TA，通过载流子迁移率、薄膜形态、电荷光生和复合的深入表征，系统地研究了这些热退火效应谱、2DES 和阻抗谱。令人惊讶的是，热退火不会改变薄膜结晶度、R-SoXS 特征尺寸尺度、相对平均相纯度或 TEM 成像相分离，而是促进 Y6 迁移到 BHJ 薄膜顶面，改变 PBDB-TF/Y6 垂直相分离和混合，并降低底面粗糙度。虽然这些形态变化增加了双分子重组 (BR) 并降低了自由电荷 (FC) 产率，但它们也将电子和空穴迁移率的平均值增加了至少两倍。重要的是，增加的 μh 在增加的 FF 和 PCE 中占主导地位并成为其基础。单晶 X 射线衍射显示 Y6 分子通过其端基/核共面堆积，最短 π-π 距离接近 3.34 Å，阐明了面外 π-face-on 分子取向纳米晶体 BHJ 域。Y6 晶体的 DFT 分析显示空穴/电子重组能低至 160/150 meV，12.1 - 37.9 meV 的大分子间电子耦合积分，合理化 3D 电子传输和相对较高的 10-4 cm2 V- 1 秒-1。综合起来，
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