Liquid‐State Dithiocarbonate‐Based Polymeric Additives with Monodispersity Rendering Perovskite Solar Cells with Exceptionally High Certified Photocurrent and Fill Factor

Abstract Dithiocarbonate‐based non‐hygroscopic polymers with a glass transition temperature (T_g) and polydispersity index (PDI) of ≈4 °C and 1, respectively, are synthesized through living cationic ring‐opening polymerization. These liquid‐state polymers are characterized by monodispersity based on the low T_g and PDI, rendering remarkable miscibility with the perovskite precursors without aggregation. Accordingly, these polymers are added to perovskite solar cells (PSCs) to enhance their power conversion efficiency (PCE). The PCE of reference PSCs increases from 19.70% to 23.52% after direct addition of the synthesized polymer. This efficiency improvement is attributed to the considerable increases in short‐circuit current density (J_SC) and fill factor (FF), resulting from the augmented size and defect passivation of perovskite crystals induced by added polymers. In fact, the PCE and J_SC of the devices measured in the laboratory and the certification center are the highest among the reported polymer‐added PSCs, thanks to the great miscibility of the new polymers leading to the large amount addition which enables more thorough passivation among the grain boundaries. The improvement in open‐circuit voltage falls short as compared to that in J_SC and FF, ascribed to the relatively moderate interaction strength between perovskite materials and dithiocarbonate groups.