Ge Jinfeng, Hong Ling, Ma Houying, Ye Qinrui, Chen Yanwei, Xie Lin, Song Wei, Li Dandan, Chen Zhenyu, Yu Kuibao, Zhang Jianqi, Wei Zhixiang, Huang Fei, Ge Ziyi
Ningbo Institute of Materials Technology and Engineering Chinese Academy of Sciences, Ningbo, 315201, P. R. China.
Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences, Beijing, 100049, P. R. China.
Adv Mater. 2022 Jul;34(29):e2202752. doi: 10.1002/adma.202202752. Epub 2022 Jun 13.
Asymmetric substitution of end-groups is first applied in molecular donors. Three commonly used end-groups of 2-ethylhexyl cyanoacetate (CA), 2-ethylhexyl rhodanine (Reh), and 1H-indene-1,3(2H)-dione (ID) are combined to construct a series of symmetric and asymmetric donors. Correspondingly, the asymmetric donors SM-CA-Reh and SM-CA-ID show largely increased dipole moments (2.14 and 3.39 D, respectively) and enhanced aggregation propensity, as compared to those of symmetric donors of SM-CA, SM-Reh, and SM-ID. Using N3 as acceptor, interestingly, SM-CA-Reh integrates the photovoltaic characteristics of high fill factor (FF) for SM-CA and high short-circuit current density for SM-Reh, and delivers a record power conversion efficiency (PCE) of 16.34% with a high FF of 77.5%, which is much higher than 15.41% for SM-CA and 14.76% for SM-Reh. However, SM-CA-ID and SM-ID give the lower PCE of 8.20% and 2.76%. Characterization results suggest that the π-π interaction mainly dictates the packing morphology of blend films instead of dipole effect or crystallinity. Mono-substitution of Reh facilitates the molecular demixing appropriately but keeps the characteristic of the fine bicontinuous network of SM-CA:N3. SM-CA-Reh:N3 shows more efficient exciton extraction, higher hole transport, and better miscibility. These results well explain the merits integration and improved photovoltaic performance.
端基的不对称取代首次应用于分子给体中。将三种常用的端基——氰基乙酸2-乙基己酯（CA）、绕丹宁2-乙基己酯（Reh）和1H-茚-1,3(2H)-二酮（ID）组合起来，构建了一系列对称和不对称给体。相应地，与对称给体SM-CA、SM-Reh和SM-ID相比，不对称给体SM-CA-Reh和SM-CA-ID的偶极矩大幅增加（分别为2.14 D和3.39 D），且聚集倾向增强。有趣的是，以N3作为受体，SM-CA-Reh兼具了SM-CA的高填充因子（FF）和SM-Reh的高短路电流密度的光伏特性，并实现了16.34%的创纪录功率转换效率（PCE），其FF高达77.5%，远高于SM-CA的15.41%和SM-Reh的14.76%。然而，SM-CA-ID和SM-ID的PCE较低，分别为8.20%和2.76%。表征结果表明，π-π相互作用主要决定了共混膜的堆积形态，而非偶极效应或结晶度。Reh的单取代适度促进了分子的相分离，但保留了SM-CA:N3精细双连续网络的特性。SM-CA-Reh:N3表现出更高效的激子提取、更高的空穴传输和更好的混溶性。这些结果很好地解释了性能的整合及光伏性能的提升。
