Impacts of 0D Cs4PbI6 phase in all-inorganic CsPbI3 perovskites on their physical, optical properties and photovoltaic performances

All-inorganic CsPbI3-based perovskite solar cells were therefore developed under a low preparation temperature of 150 °C through the control of Cs4PbI6/CsPbI3 (or 0-dimentional (0D)/3-dimentional (3D)) phase ratio (or its stoichiometry) by varying the annealing time from 0 to 30 min. In this work, it is disclosed that the stoichiometry among Cs, Pb, and I in the resulting CsPbI3 perovskite absorbers can be manipulated through the annealing time, where the 0D Cs4PbI6 phase in the films is reduced with the increase in the annealing time. The Cs4PbI6 phase in the CsPbI3 perovskites results in (i) the effective passivation of the shallow defects, thus increasing the carrier lifetime, and (ii) the suppression of the δ-CsPbI3 yellow phase, improving the phase stability. Moreover, the appropriate annealing time of 20 min gives rise to the suitable Cs4PbI6/CsPbI3 (0D/3D) phase ratio in the perovskite absorber, thereby leading to the enhanced efficiency of about 7.6%.