The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell's performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.

The light-harvesting Sb 2 S 3 surface on mesoporous-TiO 2 in inorganic-organic heterojunction solar cells is sulfurized with thioacetamide (TA). The photovoltaic performances are compared before and after TA treatment, and the state of the Sb 2 S 3 is investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and deep-level transient spectroscopy (DLTS). Although there are no differences in crystallinity and composition, the TA-treated solar cells exhibit signifi cantly enhanced performance compared to pristine Sb 2 S 3 -sensitized solar cells. From DLTS analysis, the performance enhancement is mainly attributed to the extinction of trap sites, which are present at a density of (2-5) × 10 14 cm −3 in Sb 2 S 3 , by TA treatment. Through such a simple treatment, the cell records an overall power conversion effi ciency (PCE) of 7.5% through a metal mask under simulated illumination (AM 1.5G, 100 mW cm -2 ) with a very high open circuit voltage of 711.0 mV. This PCE is, thus far, the highest reported for fully solid-state chalcogenide-sensitized solar cells.

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