Superior photoconversion efficiency of nanocrystal sensitized solar cells based on all-inorganic CsPbX₃ (X = Br, I) perovskites

Nanocrystal-sensitized solar cells have emerged as potential alternatives to traditional photovoltaic technology due to their unique light absorption and emission characteristics and size-dependent bandgap. In this work, we report the successful synthesis of cubic-phase CsPbI₃ and CsPbBr₃ nanocrystals for their use as photosensitizers in solar cells, referred to as perovskite nanocrystal-sensitized solar cells (PNCSSCs). Among the two systems, CsPbI₃ is found to be superior for PNCSSCs because of its high absorption efficiency, lower bandgap, and higher photoluminescence yield, as compared to CsPbBr₃. Our study examines the structural, compositional, optical, and electrical properties of these perovskite nanocrystals, focusing on their contributions to photoconversion efficiency. CsPbBr₃ nanocrystals exhibit a band gap of ∼2.4 eV along with defect states-induced short carrier lifetime of around 18 ns. In contrast, CsPbI₃ demonstrates a band gap of ∼1.8 eV closer to the peak of the solar spectrum with a much longer carrier lifetime of ∼130 ns, which facilitates better separation and collection of photogenerated charge carriers. Consequently, CsPbI₃ nanocrystal-sensitized solar cells fabricated with mesoporous TiO₂ reveal a photoconversion efficiency of ∼12.5%, as compared to 3.8% for CsPbBr₃ nanocrystal solar cells. To the best of our knowledge, this is the highest reported photoconversion efficiency in solution-processed perovskite nanocrystal-sensitized solar cells.