Melt-Processed Halide Perovskite Thin Films from a Two-Dimensional Ruddlesden-Popper Phase Precursor.

While halide perovskite thin films have enormous potential for photovoltaics and other optoelectronics, the use of environmentally hazardous solvents during their deposition and processing poses a barrier to their commercialization. In this work, we demonstrated the deposition of melt-processable precursors and subsequent transformation into halide perovskite thin films without using environmentally hazardous solvents. We melted the wide-bandgap layered perovskites [(C 6 H 5 CH(CH 3 )CH 2 NH 3 ) 2 PbI 4 :β-Me-PEA 2 PbI 4 ] at ∼210 °C and blade coated them into films. The β-Me-PEA 2 PbI 4 films were subsequently transformed to perovskite-phase methylammonium or formamidinium lead iodide films using a cation-exchange process in an alcohol-based solvent. Lastly, we demonstrate the potential and limitations of a completely solvent-free approach that uses solid-state transformation of a β-Me-PEA 2 PbI 4 film. This work represents a substantial step toward eliminating environmentally hazardous solvents and enables inexpensive industrial-scale liquid-phase deposition processes that do not require expensive systems for handling and disposing of environmentally hazardous solvents.