Enhanced Efficiency and Light Stability of Conventional Organic Solar Cells with a p-Type Polymeric Thin Layer on PEDOT:PSS.

Simultaneous improvement in power conversion efficiency (PCE) and device stability is very important for organic solar cells (OSCs). Herein, oligothiophene-based polymer W19 with excellent solvent resistance is exploited as a polymer thin layer to optimize the active layer morphology and then device efficiency and stability. Polymer W19 possesses a simple skeleton of trifluromethyl-substituted dithienoquinoxaline and quaterthiophene, whose thin layer shows suitable energy level, low surface energy, and strong interchain aggregation, leading to outstanding solvent resistance and excellent hole transport ability. Optimized vertical separation alleviates trap state density and energy loss, improves hole transfer dynamics, and balances the charge transport, thus maximizing open-circuit voltage, short-circuit current density, and fill factor simultaneously. A high PCE of 19.70% is achieved for the W19 treated devices. Noticeably, OSCs treated with W19 retained 87% of its initial PCE after continuous illumination for 800 h, which is higher than that of 74% of the control. Large area devices of 1 and 4 cm² can achieve high efficiencies of 17.36% and 14.46%, respectively. This work highlights that the polymer thin layer W19 with the ability of strong solvent resistance has the great potential to further improve the efficiency and photostability of OSCs.