Emergence of Deep Traps in Long-Term Thermally Stressed CH3NH3PbI3 Perovskite Revealed by Thermally Stimulated Currents

Defect states are known to trigger trap-assisted nonradiative recombination, restricting the performance of perovskite solar cells (PSCs). Here, we investigate the trap states in long-term thermally stressed methylammonium lead iodide (MAPbI₃) perovskite thin films over 500 h at 85 °C employing thermally stimulated current measurements. A prominent deep trap level was detected with an activation energy of ∼0.459 eV in MAPbI₃ without being thermally stressed. Interestingly, upon the application of thermal stress, an additional deep trap level of activation energy ∼0.414 eV emerges and grows with thermal stress duration. After 500 h of thermal stress, the trap density was ∼10¹⁶ cm^-3. The trend of open-circuit voltage loss was in line with the trap density variation with thermal stress time, which elucidates the enhanced nonradiative recombination through these trap states. This work opens a path to understanding the mechanism behind long-term thermal instability and further inspires the development of strategies to minimize trap formation in PSCs.