Probing the effective masses of halide perovskites at finite temperatures with first-principles calculations

Lattice vibrations at finite temperatures cause thermal fluctuations in atomic and electronic structures, directly modulating material properties. In conventional semiconductors like Si and GaAs, such effects are minor at room temperature, justifying the neglect of thermal effects in ground-state first-principles calculations. However, for strongly anharmonic materials such as halide perovskites, these effects are significant. Recent angle-resolved photoemission spectroscopy (ARPES) experiments on CsPbBr₃ revealed a ∼50% enhancement in the hole effective mass, which was interpreted as evidence of polaron formation. Our finite-temperature first-principles calculations show that the calculated effective mass at T = 300 K agrees well with experiments, suggesting that the ARPES experiments do not prove polaron formation in halide perovskites. Our results highlight the general importance of considering temperature effects in anharmonic materials when interpreting experimental results.