Wang Bin, Novendra Novendra, Navrotsky Alexandra
Peter A. Rock Thermochemistry Laboratory and NEAT ORU , University of California Davis , Davis , California 95616 , United States.
J Am Chem Soc. 2019 Sep 18;141(37):14501-14504. doi: 10.1021/jacs.9b05924. Epub 2019 Sep 9.
Cesium lead iodide (CsPbI) perovskite has shown great potential as a light absorbing material for solar cell applications. Despite intense research leading to increasing power conversion efficiency, a major problem concerning CsPbI lies in the long term stability and interconversion between different CsPbI polymorphs, a subject barely studied from the thermodynamic perspective. We report the formation enthalpies of two CsPbI polymorphs, α and δ CsPbI, using a combination of room temperature solution calorimetry in dimethyl sulfoxide (DMSO) and differential scanning calorimetry. We show that both polymorphs are stable with respect to their binary halides and confirm that the α-phase is a high temperature polymorph, metastable under ambient conditions. This work sheds light on patterns in polymorphism, possible decomposition reactions, materials stability, and compatibility within halide perovskites and related systems. Thermodynamic instability near ambient temperature of functional perovskites may be a general phenomenon related to their vibrational density of states.
碘化铯铅（CsPbI）钙钛矿作为太阳能电池应用中的光吸收材料已展现出巨大潜力。尽管大量研究使功率转换效率不断提高，但CsPbI存在的一个主要问题在于其长期稳定性以及不同CsPbI多晶型之间的相互转化，而从热力学角度对这一主题的研究几乎空白。我们结合在二甲基亚砜（DMSO）中进行的室温溶液量热法和差示扫描量热法，报道了两种CsPbI多晶型α和δ CsPbI的生成焓。我们表明，这两种多晶型相对于其二元卤化物都是稳定的，并证实α相是高温多晶型，在环境条件下是亚稳态的。这项工作揭示了卤化物钙钛矿及相关体系中多晶型、可能的分解反应、材料稳定性和相容性的规律。功能性钙钛矿在环境温度附近的热力学不稳定性可能是与其振动态密度相关的普遍现象。
