Due to its high chemical stability and high power conversion efficiency as a solar cell absorber, the inorganic halide perovskite, CsPbI₃, is considered one of the most promising competitors to its hybrid organic-inorganic counterpart, CH₃NH₃PbI₃. However, the phase transition from the photoactive black phase to the inactive yellow phase is a remarkable limitation that harms long-term phase stability. In particular, the phase transitions follow different pathways as the temperature increases and/or decreases, a phenomenon that is anomalous and remains poorly understood. In this study, we systematically calculated the temperature-dependent free energy of CsPbI₃ in different crystal phases (α, β, γ, δ) by considering the phonon contribution to the Gibbs free energy. It is found that the free energy results from calculations that include harmonic phonons cannot reproduce experimental observations. Alternatively, we utilized the renormalized phonon quasiparticle approach to derive the free energies of different CsPbI₃ phases at finite temperatures. Based on these calculated free energies, whose derivations included the anharmonic effect, we observed phase-transition processes consistent with experimental results. The analysis of the temperature effect on the phonon frequencies further demonstrated that anharmonic effects in the CsPbI₃ had a significant influence on its phase transitions.

中文翻译：

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显着的声子非谐驱动 CsPbI3 中的相变

由于它的高的化学稳定性和高功率转换效率的太阳能电池吸收，无机卤化物钙钛矿，CsPbI ₃，被认为是最有前途的竞争对手其杂化有机-无机对应物，CH之一₃ NH ₃碘化铅₃。然而，从光活性黑色相到非活性黄色相的相变是一个显着的限制，会损害长期相稳定性。特别是，随着温度的升高和/或降低，相变遵循不同的路径，这种现象是异常的并且仍然知之甚少。在这项研究中，我们系统地计算了 CsPbI ₃的温度依赖性自由能通过考虑声子对吉布斯自由能的贡献，在不同的晶相 (α, β, γ, δ) 中。发现由包括谐波声子在内的计算得出的自由能不能再现实验观察结果。或者，我们利用重整化声子准粒子方法来推导不同 CsPbI ₃相在有限温度下的自由能。基于这些计算出的自由能，其推导包括非谐效应，我们观察到与实验结果一致的相变过程。温度对声子频率影响的分析进一步表明，CsPbI ₃中的非谐效应对其相变有显着影响。