Thiourea-Assisted Facile Fabrication of High-Quality CsPbBr₃ Perovskite Films for High-Performance Solar Cells

Inorganic CsPbBr₃ perovskite solar cells have attracted widespread attention recently because of their decent efficiency and good ambient stability. Nevertheless, the fabrication of high-quality CsPbBr₃ perovskite via the conventional solution-processing strategy still faces great challenges because the solubility of CsBr in the conventional solvent is poor. Here, we develop a facile thiourea-assisted two-step spin-coating process to fabricate a CsPbBr₃ perovskite film with high phase purity and crystallinity and enlarged crystal grains. Thiourea is introduced into the PbBr₂ layer during the first-step spin-coating process, which promotes the wettability of the PbBr₂ layer and produces the space for growing large perovskite grains. The green high-concentration CsBr/H₂O solution is adopted at the second-step spin-coating process, enabling enough CsBr to be deposited by a facile one-step process. By optimizing the content of thiourea, a compact CsPbBr₃ perovskite film with a smooth surface, large grains, and high phase purity and crystallinity is formed. Consequently, the fabricated perovskite solar cell with the architecture of FTO/TiO₂/CsPbBr₃ film/carbon exhibits a superior performance with a high efficiency of 9.11%. In addition, the unencapsulated device preserves over 90% of its initial efficiency after storage at ambient conditions for 45 days.