Unveiling the optical, electrical, and thermodynamic properties of γ-(Cs, Rb)PbBr3

Abstract

The all-inorganic perovskite CsPbBr3 has garnered significant attention in the fields of optoelectronic devices owing to its favorable bandgap. However, CsPbBr3 undergoes polymorphic phase transitions, existing in three light-active phases: Pbnm (γ), P4/mbm (β), and Pm-3m (α). Although extensive investigations have been conducted on the α-phase, the room-temperature γ-phase has received limited investigation. The present work explores the thermodynamic properties and optoelectronic characteristics of the (Cs, Rb)PbBr3 perovskite system by means of a combinatorial density-functional-theory (DFT) and CALPHAD method. An increase in Rb doping of CsPbBr3 induces structural distortion of γ-phase, resulting in a widened bandgap from 2.12 eV to 2.28 eV. The bandgap increase will eventually lead to changes in optical properties, such as poor absorptivity and energy consumption under high Rb doping. Moderate doping enables (Cs, Rb)PbBr3 to retain the excellent optical properties and energy consumption of CsPbBr3. Especially when Rb doping is 0.25, the solid solution has the lowest reflection coefficient. The thermodynamic phase diagram shows that the solid solution (Cs, Rb)PbBr3 maintains excellent thermodynamic stability. In addition, the phase diagram quantifies the temperature range of the γ-phase, α-phase, and coexistence of two phases, which provides the theoretical guidance for the preparation of (Cs, Rb)PbBr3 solid solution films in the future.