Crystallography, Morphology, Electronic Structure, and Transport in Non-Fullerene/Non-Indacenodithienothiophene Polymer:Y6 Solar Cells

作者：Weigang Zhu, Austin P. Spencer, S. Mukherjee, Joaquin M. Alzola, Vinod K. Sangwan, Samuel H. Amsterdam, Steven M. Swick, Leighton O. Jones, Michael C. Heiber, Andrew A. Herzing, Guoping Li, Charlotte L. Stern, Dean M. DeLongchamp, Kevin L. Kohlstedt, Mark C. Hersam, George C. Schatz, Michael R. Wasielewski, Lin X. Chen, Antonio Facchetti, Tobin J. Marks · 发表于：Journal of the American Chemical Society · 年份：2020 · DOI：10.1021/jacs.0c05560 · 被引用次数：358 · 研究领域：Organic Electronics and Photovoltaics、Thin-Film Transistor Technologies、Conducting polymers and applications

Emerging nonfullerene acceptors (NFAs) with crystalline domains enable high-performance bulk heterojunction (BHJ) solar cells. Thermal annealing is known to enhance the BHJ photoactive layer morphology and performance. However, the microscopic mechanism of annealing-induced performance enhancement is poorly understood in emerging NFAs, especially regarding competing factors. Here, optimized thermal annealing of model system PBDB-TF:Y6 ( Y6 = 2,2′-((2 Z,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-1 H -indene-2,1-diylidene))dimalononitrile) decreases the open circuit voltage ( V OC ) but increases the short circuit current ( J SC ) and fill factor (FF) such that the resulting power conversion efficiency (PCE) increases from 14 to 15% in the ambient environment. Here we systematically investigate these thermal annealing effects through in-depth characterizations 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 the film crystallinity, R-SoXS characteristic size scale, relative average phase purity, or TEM-imaged phase separation but rather facilitates Y6 migration to the BHJ film top surface, ch...