Case Study on the Correlation between Crystal Packing and Miscibility of Chlorinated Thiophene–Based Donor Polymers for Nonfullerene Organic Solar Cells with Long Shelf Life

Nonfullerene organic solar cells (NFOSCs) have proven to have greater potential in terms of efficiency than fullerene-based OSCs. However, the heterogeneity of nonfullerene acceptors (NFAs)-based blend morphology is complex, making it difficult to understand, especially as its optimization requires that compatibility among the molecules be considered. Herein, P(Cl)(F = 0.5) is newly synthesized with a type of terpolymer to increase compatibility with NFAs relative to that of conventional polymers. As a result, the combination of P(Cl)(F = 0.5) with IDIC increases its power conversion efficiency (PCE) to 12.1%, compared with that of P(Cl):ITIC-Th and P(F-Cl):IT-4F. However, during the shelf life stability of optimized devices without encapsulation, a rapid decrease in the efficiency of P(Cl)(F = 0.5):IDIC and P(F-Cl):IT-4F is observed; the PCEs of P(Cl) (F = 0.5):IDIC and P(F-Cl):IT-4F decrease to 24.1% and 43.5% of their initial values for up to 350 and 398 h, respectively. On the contrary, P(Cl):ITIC-Th exhibits superior longterm air stability with a PCE decrease of −2% (for 317-h) and 9% (for 2002-h) compared with the initial PCE. To understand this phenomenon, the correlation between crystallinity and miscibility of blend films is systematically investigated. In short, the balanced crystallinity and miscibility of donor and acceptor induces a relatively more stable morphology.