Small-molecule “nonfullerene” acceptors are promising alternatives to fullerene (PC61/71BM) derivatives often used in bulk heterojunction (BHJ) organic solar cells; yet, the efficiency-limiting processes and their dependence on the acceptor structure are not clearly understood. Here, we investigate the impact of the acceptor core structure (cyclopenta-[2,1-b:3,4-b′]dithiophene (CDT) versus indacenodithiophene (IDTT)) of malononitrile (BM)-terminated acceptors, namely CDTBM and IDTTBM, on the photophysical characteristics of BHJ solar cells. Using PCE10 as donor polymer, the IDTT-based acceptor achieves power conversion efficiencies (8.4%) that are higher than those of the CDT-based acceptor (5.6%) because of a concurrent increase in short-circuit current and open-circuit voltage. Using (ultra)fast transient spectroscopy we demonstrate that reduced geminate recombination in PCE10:IDTTBM blends is the reason for the difference in short-circuit currents. External quantum efficiency measurements indicate that the higher energy of interfacial charge-transfer states observed for the IDTT-based acceptor blends is the origin of the higher open-circuit voltage.

中文翻译：

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非富勒烯受体核心结构对聚合物太阳能电池光物理和效率的影响

小分子“非富勒烯”受体有望替代通常用于体异质结（BHJ）有机太阳能电池的富勒烯（PC61 / 71BM）衍生物。然而，效率限制过程及其对受体结构的依赖性尚不清楚。在这里，我们研究了丙二腈（BM）封端的受体（CDTBM和IDTTBM，关于BHJ太阳能电池的光物理特性。由于短路电流和开路电压同时增加，使用PCE10作为供体聚合物，基于IDTT的受体实现的功率转换效率（8.4％）高于基于CDT的受体（5.6％）。使用（超）快速瞬态光谱法，我们证明了PCE10：IDTTBM共混物中降低的叠晶重组是造成短路电流差异的原因。外部量子效率测量表明，对于基于IDTT的受体混合物，观察到较高的界面电荷转移态能量是较高开路电压的来源。