Tunable Wide‐Bandgap Monohalide Perovskites

Herein the mechanochemical synthesis of inorganic as well as hybrid organic–inorganic monohalide perovskites with tunable bandgaps is reported. It is shown that the bandgap bowing known for iodide mixed Sn–Pb perovskites is also present in the pure bromide analogous. This results in technologically very interesting materials with bandgaps in the range of 1.7–1.9 eV. Similar bandgap perovskites are typically achieved by mixing two halides that are prone to segregate over time. This limits the achievable open circuit voltage. For monohalide perovskites this problem is eliminated, making these materials especially promising wide bandgap absorbers for tandem solar cells. This work highlights several pure‐bromide perovskites with ideal bandgaps for top‐cell absorbers in photovoltaic tandems. This is achieved by taking advantage of the bandgap‐bowing behavior of mixed tin–lead perovskites. Nontemplated samples as well as thin films are prepared by several routes including solvent‐free mechanochemical synthesis, spin‐coating, and single‐source thermal vacuum deposition.