Two‐Photon Absorption in Perovskite Semiconductors

ABSTRACT Perovskite semiconductors have emerged as promising materials for nonlinear photonic, optoelectronic, and energy‐conversion applications, yet a predictive theory of two‐photon absorption (TPA) in these materials remains incomplete. The existing TPA models were primarily developed for conventional semiconductors and neglect the unique band‐structure characteristics of perovskites. In this work, we have developed an analytical model for the TPA coefficient, K 2 , in perovskite semiconductors using second‐order perturbation theory within the parabolic‐band framework, including excitonic effects. The model incorporates the inter‐ and intra‐band transitions associated with the heavy‐electron, light‐electron, and spin–orbit split‐off conduction band states. Numerical calculations performed for representative perovskite materials show good agreement between theory and experiment over a wide temperature range, including TPA coefficients at 290 and 50 K. The results highlight the importance of accounting for the band structure, excitonic and relativistic effects when analyzing TPA spectra in perovskite semiconductors and lay the foundation for the design of perovskite‐based nonlinear optical and photonic devices.