Motivated by the contentious photoluminescence microscopic physics of CsPbX (X = Br, I), this paper employs first-principles calculation and a Hamiltonian model to investigate the structural distortion and oscillator strength of exciton in CsPbX perovskite. The findings reveal that the polymorphous CsPbX with distorted octahedral exhibits greater stability and a larger band gap compared to the ideal cubic phase, thereby directly explaining the previously underestimated band gap. Our calculations also predicate the presence of two distinct peaks in the photoluminescence spectra of the polymorphous CsPbBr, corresponding to bright and exciton states.

中文翻译：

---

多晶型 CsPbX3 钙钛矿的结构畸变和激子行为

受 CsPbX (X = Br, I) 有争议的光致发光微观物理的启发，本文采用第一性原理计算和哈密顿模型研究 CsPbX 钙钛矿中激子的结构畸变和振荡强度。研究结果表明，与理想立方相相比，具有扭曲八面体的多晶型CsPbX表现出更高的稳定性和更大的带隙，从而直接解释了之前被低估的带隙。我们的计算还预测多晶型 CsPbBr 的光致发光光谱中存在两个不同的峰，对应于亮态和激子态。