Photo‐Induced Degradation of 2D Dion−Jacobson Perovskites under Continuous Light Illumination

In the past decade, there has been a rapid development in perovskite solar cells, and their highest device efficiency has reached 25.7%. But their poor stability is still one of the critical factors hindering commercialization. Compared with 3D‐structured perovskites, 2D perovskites have better structural stability especially 2D Dion−Jacobson (D–J) perovskites. However, their degradation mechanism under light is not clear. Herein, the changes in the absorption spectra of D–J perovskites (PDA(FA) n −1 Pb n I 3 n −1 ) under continuous light illumination (100 mW cm −2 ) are investigated. The absorption spectra of D–J perovskites with different n values change in different degrees after two hours of continuous light illumination. It is found that the absorption intensity near the band edge of all these films has been enhanced, which indicates that some more absorbing species are produced. X‐Ray diffraction patterns confirm that the PDA(FA) n −1 Pb n I 3 n −1 2D D–J perovskite is transformed into 3D α‐FAPbI 3 after illumination, and further transformed into δ‐FAPbI 3 and PbI 2 . The proposed work contributes to understanding the degradation mechanism of 2D D–J perovskite under illumination and improving the stability of 2D D–J perovskite materials.