In-situ surface defects passivation with small carbon chain molecules for highly efficient, air-processed inorganic CsPbI2Br perovskite photovoltaics

All-inorganic CsPbI2Br perovskites have gained enormous interests owing to suitable band gap and thermal stability. However, the CsPbI2Br suffers from unsatisfactory crystal growth and poor surfaces processed under ambient conditions. Herein, we introduced small carbon chain molecules as liquid additives including diiodomethane (DIM), dibromoethane (DBM), and dichloromethane (DCM) into the precursor. The halide ions as associated with these additives played vital roles to passivate the surface defects. Interestingly, DIM additive offers multiple benefits: (i) passivate uncoordinated Pb2+ dangling bonds (ii) match band energy alignment, (iii) assist to preferential oriented crystal growth (iv) suppress halide ion vacancies and (v) improve surface morphology. As a result, 100 μl DIM-assisted perovskite solar cell (PSC) exhibited the highest power conversion efficiency (PCE) of 16.42 % which is higher than that of control (13.95 %). Notably, with additive engineering approach our champion PCE (16.42 %) is the highest to date under processing at ambient conditions. On the contrary to poor stability of control PSC (PCE drop of ∼ 50 %), the DIM assisted PSC retained ∼ 80 % of original PCE after aging for 600 hrs. Thus, our photovoltaic results demonstrated that the additive method could open an effective route for development of efficient and stable PSCs under ambient conditions.