All-Inorganic, Solution-Processed, Inverted CsPbI3 Quantum Dot Solar Cells with a PCE of 13.1% Achieved via a Layer-by-Layer FAI Treatment

All-inorganic CsPbI3 perovskite quantum dots (PQDs) are promising photovoltaic materials due to their exceptional electronic properties, including tunable bandgap, high photoluminescence (PL) quantum yields, and enhanced electronic properties due to tunable surface chemistry. Charge transport in solid-state films can be further improved by manipulating surface chemistry, which enhances better coupling of neighboring QDs. Here, we have fabricated an all-inorganic CsPbI3 QD solar cell (QDSC) in an inverted (p-i-n) configuration using inorganic selective contact layers for charge transport. Additionally, we have improved the solid-state ligand exchange process using a layer-by-layer (LBL) deposition method for ligand replacement in the QD films. Specifically, we have removed native ligands such as anionic oleate and cationic oleylammonium ligands using methyl acetate and formamidinium. This mixture enables the efficient removal of ligands and provides strong inter-QD coupling during each LBL deposition step. The ligand replacement helps in improving the film morphology by curing voids originating from volume loss through LBL assembly in addition to improving strong coupling while preserving quantum confinement. As a result, the inverted CsPbI3 QD solar cell exhibits power conversion efficiencies (PCEs) of 13.1% with 5 photoactive layers and 12.1% with only 3 layers, both with negligible hysteresis. Most importantly, we achieve improved efficiency in an efficient solution-processed device with fewer fabrication steps and superior transparency versus most n-i-p devices.