Effect of Co-passivation on CsPbI2Br perovskite solar cells with increased photovoltaic efficiency

Abstract

All-inorganic perovskites CsPbI₂Br have gained much research interest in photovoltaics due to their excellent thermal stability. However, all-inorganic perovskite solar cells (PSCs) are prone to form defective perovskite films, which are detrimental to their high power conversion efficiencies (PCEs). In this study, CsPbI₂Br PSCs with improved PCEs have been developed by introducing 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) and tris(2-aminoethyl)amine (TAEA) as co-passivators. It is shown that BMIMBF₄ additive improves the quality of perovskite films with reduced defect density, enhanced device efficiency, and increased phase stability in ambient atmosphere. By using TAEA as a co-passivator, the non-radiative recombination of PSCs is further suppressed, which cannot be achieved by BMIMBF₄ alone. Moreover, after treating the perovskite surface with TAEA, the activation energy for ion migration is increased. The decelerated ion migration in CsPbI₂Br solar cells leads to the illusion of a larger hysteresis effect but results in a higher steady-state output efficiency. The steady-state PCE of the optimized CsPbI₂Br solar cells increased from 7.2 % to 11.3 %.