Understanding the Phase Transition of FAPbI₃ Films through In Situ Raman Studies for Enhanced Solar Cell Performance

Perovskite solar cells have attracted considerable attention because of their potential to achieve high efficiency at low costs. In this study, the temperature-dependent phase transitions and decomposition pathways of formamidinium lead iodide (FAPbI₃) thin films were studied using in situ Raman spectroscopy. FAPbI₃ is a promising material for perovskite solar cells due to its narrow bandgap and high thermal stability. This study explores the evolution of the photoactive α-phase and metastable intermediate phases during thermal annealing over a temperature range of -150 to 250 °C by in situ Raman spectroscopy at ambient conditions. Also, annealing at 125, 150, and 175 °C under an inert atmosphere resulted in systematic tuning of the optical bandgap, as confirmed by photoluminescence measurements and Tauc plot analysis. XRD and Raman spectroscopy revealed the presence of mixed phases at lower temperatures and stabilization of the cubic α-phase at higher temperatures. SEM imaging correlated the annealing temperature to morphological changes, showing improved crystallinity and film quality at higher temperatures. These findings provide valuable insights into the phase formation behavior and thermal evolution of FAPbI₃ films, contributing to the development of more stable and efficient perovskite solar cells with improved performance. The comprehensive exploration of crystallization mechanisms through Raman studies and phase transition dynamics helps to address one of the most pressing challenges: structural stability in the FAPbI₃ perovskite.