Wang Gang, Swick Steven M, Matta Micaela, Mukherjee Subhrangsu, Strzalka Joseph W, Logsdon Jenna Leigh, Fabiano Simone, Huang Wei, Aldrich Thomas J, Yang Tony, Timalsina Amod, Powers-Riggs Natalia, Alzola Joaquin M, Young Ryan M, DeLongchamp Dean M, Wasielewski Michael R, Kohlstedt Kevin L, Schatz George C, Melkonyan Ferdinand S, Facchetti Antonio, Marks Tobin J
Material Science and Engineering Division , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.
X-ray Science Division , Argonne National Laboratory , Argonne , Illinois 60439 , United States.
J Am Chem Soc. 2019 Aug 28;141(34):13410-13420. doi: 10.1021/jacs.9b03770. Epub 2019 Aug 16.
Achieving efficient polymer solar cells (PSCs) requires a structurally optimal donor-acceptor heterojunction morphology. Here we report the combined experimental and theoretical characterization of a benzodithiophene-benzothiadiazole donor polymer series (PBTZF4-R; R = alkyl substituent) blended with the non-fullerene acceptor ITIC-Th and analyze the effects of substituent dimensions on blend morphology, charge transport, carrier dynamics, and PSC metrics. Varying substituent dimensions has a pronounced effect on the blend morphology with a direct link between domain purity, to some extent domain dimensions, and charge generation and collection. The polymer with the smallest alkyl substituent yields the highest PSC power conversion efficiency (PCE, 11%), reflecting relatively small, high-purity domains and possibly benefiting from "matched" donor polymer-small molecule acceptor orientations. The distinctive morphologies arising from the substituents are investigated using molecular dynamics (MD) simulations which reveal that substituent dimensions dictate a well-defined set of polymer conformations, in turn driving chain aggregation and, ultimately, the various film morphologies and mixing with acceptor small molecules. A straightforward energetic parameter explains the experimental polymer domain morphological trends, hence PCE, and suggests strategies for substituent selection to optimize PSC materials morphologies.
要实现高效的聚合物太阳能电池（PSC），需要结构上优化的供体-受体异质结形态。在此，我们报告了与非富勒烯受体ITIC-Th共混的苯并二噻吩-苯并噻二唑供体聚合物系列（PBTZF4-R；R = 烷基取代基）的实验和理论联合表征，并分析了取代基尺寸对共混物形态、电荷传输、载流子动力学和PSC指标的影响。改变取代基尺寸对共混物形态有显著影响，在一定程度上，域纯度、域尺寸与电荷产生和收集之间存在直接联系。具有最小烷基取代基的聚合物产生了最高的PSC功率转换效率（PCE，11%），这反映出相对较小的高纯度域，并且可能受益于“匹配”的供体聚合物-小分子受体取向。使用分子动力学（MD）模拟研究了由取代基产生的独特形态，结果表明取代基尺寸决定了一组明确的聚合物构象，进而驱动链聚集，并最终导致各种薄膜形态以及与受体小分子的混合。一个简单的能量参数解释了实验中聚合物域形态趋势，从而解释了PCE，并提出了选择取代基以优化PSC材料形态的策略。
