Differences in the Stability of 2D Ruddlesden–Popper Lead- and Tin-Based Perovskites

It is well known that Sn-based halide perovskites are less stable than Pb-based ones and 2D halide perovskites are more stable compared with 3D perovskites. Thus, understanding the degradation of 2D Sn-based perovskites is particularly important. However, although differences in degradation between Pb- and Sn-based 3D perovskites have been extensively investigated, comparative investigations of 2D Pb- and Sn-based perovskites have been scarce. Thus, herein, we investigate the degradation of A2PbI4 and A2SnI4 2D Ruddlesden–Popper perovskites for two different spacer cations, 2-thiopheneethylammonium (TEA) and 4-fluorophenethylammonium (FPEA). We observe significant differences in degradation products for Sn- and Pb-based perovskites. In Sn-based 2D perovskites, crystalline TEAI/FPEAI is observed in aged A2SnI4, and there is no evidence of spacer cation decomposition, while in A2PbI4, clear outgassing of NH3 is observed under illumination. This indicates a significant difference in degradation pathways for A2SnI4 and A2PbI4 perovskites, which can be attributed to differences in the redox chemistry of constituent ions. As the stability of A2SnI4 significantly lags behind that of A2PbI4, different additives were investigated to further improve the stability of TEA2SnI4.