Achieving 19% efficiency in nonfused ring electron acceptor solar cells via solubility control of donor and acceptor crystallisation

Nonfused ring electron acceptors (NFREAs) are interesting n-type near infrared (NIR) photoactive semiconductors with strong molecular absorption and easy synthetic route. However, the low backbone planarity and bulky substitution make NFREA less crystalline, which significantly retards charge transport and the formation of bicontinuous morphology in organic photovoltaic device. Donor and acceptor solubility in different solvents is studied, and the created solubility hysteresis can induce the formation of the highly crystalline donor polymer fibril to purify the NFREA phase, thus a better bicontinuous morphology with improved crystallinity. Based on these results, a general solubility hysteresis sequential condensation (SHSC) thin film fabrication methodology is established to produce highly uniform and smooth photoactive layer. The well-defined interpenetrating network morphology afforded a record efficiency of 19.02%, which is ~22% improvement comparing to conventional device fabrication. A high efficiency retention (Pr) value of 92.3% is achieved in 1 cm² device (17.28% efficiency).

非稠环电子受体（Nonfused Ring Electron Acceptors, NFREAs）是一类极具应用潜力的n型近红外（Near Infrared, NIR）光活性半导体，兼具强分子吸收能力与简便的合成路径。然而，主链平面性不足与大位阻取代基导致NFREAs结晶性较差，这极大阻碍了有机光伏器件内的电荷传输与双连续活性层形貌的形成。研究团队针对给体、受体在不同溶剂中的溶解度开展了系统研究，发现其产生的溶解度滞后效应可诱导高结晶度给体聚合物纤维的形成，进而实现NFREA相的纯化，最终获得结晶性更优的双连续活性层形貌。基于上述发现，我们构建了一套通用的溶解度滞后顺序冷凝（Solubility Hysteresis Sequential Condensation, SHSC）薄膜制备工艺，可制备出高度均匀平整的光活性层。该工艺所得到的规整互穿网络形貌，实现了19.02%的纪录级光电转换效率，较传统器件制备方法提升约22%。在面积为1 cm²的器件中，其效率保留率（Efficiency Retention, Pr）可达92.3%，对应器件效率为17.28%。