Approaching Full-Scale Passivation in Perovskite Solar Cells via Valent-Variable Carbazole Cations

Hybrid halide perovskite solar cells (PSCs) have emerged as the next-generation photovoltaic technology. Compared to steady silicon solar cells, PSCs are facilely processable but easily generate defects/traps during the thin-film fabrication from the solution. To passivate these defects, which have been considered as the origin of PSC instability, numerous large-sized organic cations (LSOCs) were applied via post-treatment methods. Unfortunately, along with the passivation on defects, these LSOCs could also react with regular perovskite phases and convert them into layered perovskite phases with poorer optoelectronic performances. Herein, we have designed carbazole ethylammonium iodide (CzEAI), a LSOC salt which exhibits a variation from monovalent to divalent state. Importantly, unlike traditional LSOC passivators in monovalent states mostly consumed by a regular perovskite phase and merely affecting the upper domain in thin films, CzEA in monovalent state could penetrate through the whole domain in perovskite films and then accurately convert into a divalent state at defect sites and thus realize a full-scale passivation in PSCs. Both simulation and experimental results proved that a CzEA passivator could overcome the formation of poor optoelectronic layered perovskite phases. As a result, the CzEA passivated PSC demonstrated an optimized photon-to-electron conversion efficiency (PCE) of 24.14% together with a significantly improved long-term stability over 5000 h.