Methylammonium bismuth iodide ((CH3NH3)3Bi2I9, MBI) is a promising alternative to perovskite solar cells (PSCs) due to its air stability and low-toxicity. Herein, a two-stage electric-field-assisted reactive deposition method has been introduced to prepare MBI films for the first time. PSCs based on MBI films were fabricated and characterized. The influences of electric parameters (applied voltage mode, pulse and time, etc.) on the morphology and crystal structure of MBI film correlated with the photovoltaic performance of PSCs have also been investigated systematically in detail. Through adjusting the voltage mode, crystal growth can be completely controlled, leading to a compact MBI film with large grain size. Moreover, the MBI film prepared by electrochemical deposition required no annealing. This work determined that the optimal performance of PSCs is based on the MBI film deposited by square-wave (AC) voltage mode (−7.3 V/+1 V, 5 Hz, 5 min). All devices exhibited long-term stability in ambient air (humidity of >50%) for more than 300 h. This study will inspire further research on the application of electrochemical deposition technique for other lead-free PSCs.
