Carboxylate‐Containing Poly(thiophene vinylene) Derivative with Controlled Molecular Weights for High‐Performance Intrinsically‐Stretchable Organic Solar Cells

Abstract Owing to their simple chemical structures and straightforward synthesis, poly(thiophene vinylene) (PTV) derivatives are promising types of polymer donors for organic solar cells (OSCs). However, the structural rigidity of PTVs results in the formation of films with poor mechanical properties, which limits the application of PTVs in intrinsically stretchable (IS)‐OSCs. Here, new carboxylate‐containing PTVs are developed with tuned molecular weight (MW) (PETTCVT‐X, X = L, M, and H) and realize efficient and mechanically durable IS‐OSCs. The crystallinity of the PTVs increases progressively with increasing MW, leading to enhanced hole mobility and suppressed charge recombination of the OSCs. Moreover, both the mechanical stretchability and electrical properties of the PTVs increase significantly with increasing MW, owing to the formation of tie‐chains that connect the isolated crystalline domains. Consequently, OSCs featuring a PTV with the highest MW (PETTCVT‐H) exhibit the highest power conversion efficiency (PCE, 15.3%) and crack‐onset strain (COS, 7.1%) among the series, compared to lower values for the PETTCVT‐L (PCE = 9.7% and COS = 1.3%) and PETTCVT‐M‐based OSCs (PCE = 12.5% and COS = 3.7%). Therefore, the IS‐OSCs employing PETTCVT‐H present the highest initial PCE (10.1%) and stretchability (strain at PCE 80% (retaining 80% of the initial PCE) = 16%).