Applicationof a Fluorene-Based Conjugated Polyelectrolyteas an Antisolvent Additive for a Stable Perovskite Layer

In perovskite solar cells (PSCs), the small size of the perovskite grains and the presence of grain boundary defects lead to uneven surface morphology, deteriorating the device efficiency and stability. Here, a fluorene-based conjugated polyelectrolyte (FF-BOC) is designed and introduced as an antisolvent additive in the one-step perovskite preparation process. During the formation of the perovskite grains, multiple interactions between functional groups of FF-BOC and the components of MAPbI₃, including opposite charges’ attraction between COO^– and MA⁺, hydrogen bonding between NH and I^–, and coordination bonding between O atoms and Pb²⁺, not only improve the crystallinity and deliver surface uniformity of the perovskite film but also decrease the boundary defects between the perovskite grains. Through the antisolvent modification with an optimal FF-BOC concentration of 0.5 mg mL^–1, the photovoltaic performance of the unencapsulated device was improved with a maximum power conversion efficiency (PCE) of 22.52% and excellent stability without any degradation after 60 days in an air environment with a relative humidity of 25–40%.