Unraveling UV Stability in Metal Halide Perovskites: From Degradation Mechanisms to Molecular Passivation

Understanding the mechanisms of UV-induced degradation is crucial for enhancing the UV stability of perovskite solar cells. The UV-driven structural dynamics of CH₃NH₃PbI₃ (MAPbI₃) are investigated using real-time TDDFT simulations, revealing that under the electron and hole excitation, the distortion of the inorganic framework is primarily driven by the electron occupation of Pb-p and I-p antibonding states, whereas in the hole case, it is mainly governed by the direct cooling induced distortion. We also found that UV accelerates the rotation of MA⁺ molecules. Further, a BDO molecule is introduced as a passivant, which suppresses structural distortions and provides multiphonon channels to dissipate carrier cooling energy. Experimental results confirm the UV-protective role of BDO, with suppressed PbI₂ formation and improved device stability. These results clarify the mechanism of UV-induced degradation in the MAPbI₃ perovskite and further elucidate how passivation molecules enhance the UV stability.