Stable Bandgap-Tunable Hybrid Perovskites with Alloyed Pb-Ba Cations for High-Performance Photovoltaic Applications.

The intrinsic poor stability of MAPbI hybrid perovskites in the ambient environment remains as the major challenge for photovoltaic applications. In this work, complementary first-principles calculations and experimental characterizations reveal that metal cation alloyed perovskite (MABa PbI) can be synthesized and exhibit substantially enhanced stability via forming stronger Ba-I bonds. The Ba-Pb alloyed perovskites remain phase-pure in ambient air for more than 15 days. Furthermore, the bandgap of MABa PbI is tailored in a wide window of 1.56-4.08 eV. Finally, MABa PbI is used as a capping layer on MAPbI in solar cells, resulting in significantly improved power conversion efficiency (18.9%) and long-term stability (>30 days). Overall, our results provide a simple but reliable strategy toward stable less-Pb perovskites with tailored physical properties.