Atomistic Origins of Enhanced Band Gap, Miscibility, and Oxidation Resistance in α‑CsPb1–xSnxI3 Mixed Perovskite

The advance made in perovskite-based solar cell technology demands the search for materials with better properties, namely, high stability in operational conditions and suitable electronic structure parameters. In this work, we provide a detailed study for cubic CsPb1–xSnxI3 alloys. We employed a theoretical model that combines quasiparticle effects via the density functional theory (DFT)-1/2 method and spin–orbit corrections with a rigorous statistical disordered description of the alloy. As the main result, a reliable quantitative expression for the variation of energy gap with the composition that can be directly compared with experiments is given. A particular situation is verified for x = 0.80, where the alloy is predicted to have a band gap of 0.984, 0.033 eV lower than the gap of CsSnI3. Additionally, the model encompasses the nuances necessary to understand the properties’ behavior in this complex system. We verified that “more mixed” configurations are energetically favored, leading to ordering in very small temperatures that evolve to a very stable alloy in the usual growth conditions. Also, based on the thermodynamic results, an antioxidant mechanism for this alloy is proposed. The bowing mechanism is explained in terms of band character and spin–orbit interaction. Finally, the conclusions support CsPb1–xSnxI3 alloys as a very good potential candidate for photovoltaic applications.

钙钛矿基太阳能电池技术的发展亟需开发性能更优异的材料，具体需满足运行稳定性优异、电子结构参数适配两大要求。本研究针对立方相CsPb₁₋ₓSnₓI₃合金开展了详尽的理论分析。我们采用了结合基于密度泛函理论（DFT）-1/2方法的准粒子效应、自旋轨道修正，以及对合金进行严谨统计无序描述的理论模型。作为核心研究成果，本工作给出了可直接与实验结果对比的、描述带隙随组分变化的可靠定量表达式。针对x=0.80的特殊组分，我们预测该合金的带隙为0.984 eV，比纯CsSnI₃的带隙低0.033 eV。此外，本模型涵盖了理解该复杂体系中材料性能演化规律所需的关键细节。研究发现，“混合度更高”的原子构型在能量上更具优势，会在极低温度下形成有序结构，并在常规生长条件下演变为高度稳定的合金。基于热力学计算结果，本研究还提出了该合金的抗氧化机制。我们从能带特征与自旋轨道相互作用的角度阐释了带隙弯曲效应。最后，研究结论证实CsPb₁₋ₓSnₓI₃合金是极具潜力的光伏应用候选材料。