Random Copolymers Outperform Gradient and Block Copolymers in Stabilizing Organic Photovoltaics

Recent advances have led to conjugated polymer‐based photovoltaic devices with efficiencies rivaling amorphous silicon. Nevertheless, these devices become less efficient over time due to changes in active layer morphology, thereby hindering their commercialization. Copolymer additives are a promising approach toward stabilizing blend morphologies; however, little is known about the impact of copolymer sequence, composition, and concentration. Herein, the impact of these parameters is determined by synthesizing random, block, and gradient copolymers with a poly(3‐hexylthiophene) (P3HT) backbone and side‐chain fullerenes (phenyl‐C61‐butyric acid methyl ester (PC61BM)). These copolymers are evaluated as compatibilizers in photovoltaic devices with P3HT:PC61BM as the active layer. The random copolymer with 20 mol% fullerene side chains and at 8 wt% concentration in the blend gives the most stable morphologies. Devices containing the random copolymer also exhibit higher and more stable power conversion efficiencies than the control device. Combined, these studies point to the random copolymer as a promising new scaffold for stabilizing bulk heterojunction photovoltaics. Photovoltaic devices made from conjugated polymers now exhibit efficiencies rivaling amorphous silicon; however, the poor longevity of these devices continues to stymie their commercial impact. Copolymer additives represent a promising solution, yet little is known about how the copolymer sequence, composition, and concentration influence their compatibilizing abilities. Herein, random copolymer additives lead to higher efficiency and longer‐lasting photovoltaic devices.