High-Purity, Thick CsPbCl₃ Films toward Selective Ultraviolet-Harvesting Visibly Transparent Photovoltaics

Inorganic lead halide perovskite CsPbCl3 with an absorption edge of ∼420 nm and exceptional optoelectronic properties is promising for selective ultraviolet (UV)-harvesting visibly transparent photovoltaics. However, the low solubilities of CsCl and PbCl2 precursor materials in common solvents make it difficult to prepare high-quality CsPbCl3 films with the desired thickness. Herein, we demonstrate a water-assisted two-step spin coating growth strategy for CsPbCl3 films. Because of the high solubility of CsCl but the low solubility of PbCl2 in water, it becomes possible to produce CsPbCl3 films by direct spin coating of CsCl/H2O solution onto a PbCl2 film without damaging it. After optimizing the dose of CsCl/H2O solution, CsPbCl3 films with a full surface coverage, pure perovskite phase, high crystallinity, large average grain size of 620 nm, and thickness of ∼310 nm are obtained. Consequently, the selective UV-harvesting visibly transparent PSCs with the CsPbCl3 films yield an optimized efficiency of 1.19%, an average visible transparency of 53.1%, and a color rendering index of 91.1. The findings of our study make it clear that the water-assisted two-step spin coating growth strategy is highly feasible to prepare CsPbCl3 films with desired characters, and thus, it has a great potential in the future development of CsPbCl3 optoelectronic devices.