First-principles calculations of the effect of X-site halogen composition ratio on the stability of vacuum deposited CsPbI x Br 3− x -based perovskite films

Abstract Perovskite films are unstable in the presence of water and oxygen, they undergo phase transition, losing their photovoltaic-active cubic crystal lattice structure. One strategy to improve long term-stability is to change the size of the ions constituting the perovskite crystal. In this work, we investigate the stability of CsPbI x Br 3− x ( x = 0, 1, 2, 3) perovskite materials using the decomposition energy (Δ H ) calculated from first-principles. First-principles calculations provide insights into physical properties and structures. The calculated Δ H of CsPbBr 3 is larger than their CsPbI 3 , CsPbI 2 Br and CsPbIBr 2 counterparts, suggesting that a sufficiently large value limits change from the black phase of perovskite. We compared experimental results with the outcome from first-principles calculations and correlated them with X-ray diffraction, and UV–vis results. This work provides a fundamental vision into the thermal stability of perovskite crystals.