Octylammonium iodide modification of electrodeposition-converted PbI2 for fabricating efficient and stable perovskite solar cells

Electrodeposited perovskite solar cells suffer from limited efficiency (historically below 15%). This study shows that spin coating octylammonium iodide (OAI) onto electrodeposition-converted PbI2 precursors results in significantly enhanced device performance and stability. The optimized OAI modification increases the power conversion efficiency (PCE) from 18.38% to 21.21%, with simultaneous improvements in fill factor (FF), open-circuit voltage (Voc), and short-circuit current density (Jsc). The OAI-modified devices retain 84% of their initial PCE after 1032 h in an N2 glovebox, far exceeding the stability of control devices (whose PCE decreases to 76% within 312 h). Systematic characterization reveals that OAI first interacts with undercoordinated Pb2+ on PbI2, forming an OA2PbI4 intermediate phase that templates perovskite growth. This process yields enlarged grains, eliminates parasitic PbI2 aggregates, and enhances the crystallinity of perovskite. Then, the residual OAI molecules passivate key defects (undercoordinated Pb2+ and halides) at grain boundaries and interfaces via chemical interaction and steric stabilization effects. This results in significantly reduced trap density, suppressed nonradiative recombination, and enhanced charge extraction kinetics. The combination of optimized morphology, superior crystallinity, and effective defect suppression yields simultaneous improvements in all photovoltaic parameters (PCE, Jsc, Voc, FF), along with unprecedented operational stability for electrodeposited perovskite solar cells. Hence, this work revitalizes electrodeposition as an advanced, inexpensive, and reproducible route for fabricating PSCs, demonstrating its enormous application potential in these devices.