Efficient Planar Perovskite Solar Cells Based on 1.8 eV Band Gap CH3NH3PbI2Br Nanosheets via Thermal Decomposition

Hybrid organometallic halide perovskite CH₃NH ₃PbI₂Br (or MAPbI₂Br) nanosheets with a 1.8 eV band gap were prepared via a thermal decomposition process from a precursor containing PbI₂, MABr, and MACl. The planar solar cell based on the compact layer of MAPbI₂Br nanosheets exhibited 10% efficiency and a single-wavelength conversion efficiency of up to 86%. The crystal phase, optical absorption, film morphology, and thermogravimetric analysis studies indicate that the thermal decomposition process strongly depends on the composition of precursors. We find that MACl functions as a glue or soft template to control the initial formation of a solid solution with the main MAPbI₂Br precursor components (i.e., PbI₂ and MABr). The subsequent thermal decomposition process controls the morphology/surface coverage of perovskite films on the planar substrate and strongly affects the device characteristics.