Preparation of nanoscale inorganic CsPbI_xBr_3-x perovskite photosensitizers on the surface of mesoporous TiO₂ film for solid-state sensitized solar cells

Metal chalcogenide quantum dot (QD)-like all-inorganic nanoscale perovskite photosensitizers of CsPbI_xBr_3-x were prepared on the surface of mesoscopic TiO₂ film by a direct two-step spin-coating of lead and cesium halide precursors for application into solid-state dye-sensitized solar cells (DSSCs), as confirmed by impedance frequency response analysis. A few nanometer-sized hemisphere-shaped dots of CsPbI_xBr_3-x perovskites were deposited and distributed separately onto TiO₂, which were checked by scanning and transmission electron microscopic (SEM and TEM) techniques. The as-deposited CsPbI_xBr_3-x perovskites were stable only in the case of including about 20% or more bromide in the composition of halides. When the bromide content increased in the ratio of halides of CsPbI_xBr_3-x, gradual decrease in lattice spacing and blue-shift of emission peaks were observed in X-ray diffraction (XRD) and photoluminescence (PL) measurements, respectively. These well-defined nano-particulate CsPbI_xBr_3-x perovskites were incorporated into solid-state DSSCs and tested as a new type of photosensitizers. The initial power conversion efficiency (PCE) of ca. 1.0–3.5% based on relatively thin mesoporous TiO₂ film (~1 μm) looks promising with many parameters remaining for possibly more optimization. The best result, 3.79%, was obtained from CsPbI_2.2Br_0.80 25 days after initial measurement. These CsPbI_xBr_3-x-sensitized cells displayed a stable record of PCE over ~2 month and no hysteresis behavior in current-voltage traces.