Compositional and Defect Engineering of Metal Halide Perovskite‐Based Heterojunctions for Efficient Nitrogen Photofixation

Designing innovative photocatalysts for nitrogen photofixation is becoming crucial for the development of carbon‐neutral ammonia production. Metal halide perovskites (MHPs) provide a rich library of materials with an easy tuning of the semiconductor bandgap in order to integrate them in devices with different functionalities. An under‐explored path is their exploitation to run a wide range of photoredox reactions mediated by solar light. Herein, heterojunction is developed based on the vacancy‐ordered double‐perovskite Cs 2 SnBr 6 and carbon nitride nanosheets and demonstrate its ability in running the nitrogen photofixation reaction to produce ammonia under solar light. An investigation is done on full Cs 2 SnBr 6 /g‐C 3 N 4 system and an optimal range providing an outstanding ammonia evolution rate up to 270 μmol g −1 h −1 is identified, which is quantified by means of ion selective electrode. Mechanistic insight into the photofixation reaction is obtained through a combination of advanced spectroscopy and computational modeling. Efficient ammonia production stems from an effective charge transfer from the perovskite to the nitrogen vacancies on the carbon nitride enabled by the proposed absence of self‐trapped excitons in Cs 2 SnBr 6 , which also provides additional reactive sites through bromide vacancies. This work paves the way to MHP‐based catalyst design strategy for sustainable ammonia production.