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

Hybrid halide perovskite solar cells(PSCs) have emergedas thenext-generation photovoltaic technology. Compared to steady siliconsolar cells, PSCs are facilely processable but easily generate defects/trapsduring the thin-film fabrication from the solution. To passivate thesedefects, which have been considered as the origin of PSC instability,numerous large-sized organic cations (LSOCs) were applied via post-treatmentmethods. Unfortunately, along with the passivation on defects, theseLSOCs could also react with regular perovskite phases and convertthem into layered perovskite phases with poorer optoelectronic performances.Herein, we have designed carbazole ethylammonium iodide (CzEAI), aLSOC salt which exhibits a variation from monovalent to divalent state.Importantly, unlike traditional LSOC passivators in monovalent statesmostly consumed by a regular perovskite phase and merely affectingthe upper domain in thin films, CzEA in monovalent state could penetratethrough the whole domain in perovskite films and then accurately convertinto a divalent state at defect sites and thus realize a full-scalepassivation in PSCs. Both simulation and experimental results provedthat a CzEA passivator could overcome the formation of poor optoelectroniclayered perovskite phases. As a result, the CzEA passivated PSC demonstratedan optimized photon-to-electron conversion efficiency (PCE) of 24.14%together with a significantly improved long-term stability over 5000h.