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• A simple solvent engineering strategy was employed to control morphology of PbI 2 films effectively by water processing. • Platelet-like PbI 2 films can successfully control the residual amount of PbI 2 in perovskite film. • Platelet-like PbI 2 films can control the morphology of the perovskite film and improve the device efficiency [Display omitted] The performance of organic-inorganic perovskite solar cells depends largely on the quality of perovskite film. Currently, various methods are applied to prepare the perovskite film. Among them, the two-step method is counted as a promising candidate to obtain high-quality perovskite film. In this study, we attain a special platelet-like PbI 2 films by applying pure water to cover wet PbI 2 film and standing for a period of time. The unique morphology contributes to the entry of organic cations solution into the PbI 2 and promoting its reaction with PbI 2 , which reducing the residual amount of PbI 2 in the perovskite film. Compared to the traditional two-step method, water processing method can obtain a high-quality perovskite film with enlarged grain size, improved crystallization, and prolonged carrier lifetime. As a result, the efficiency of the prepared device based on the film has increased from 17.90% without water processing to 20.14% of water processing. Which demonstrates that this solvent engineering for PbI 2 film opens up a possibility to prepare high-quality perovskite in a two-step method and obtain highly efficient perovskite solar cells. [ABSTRACT FROM AUTHOR]

Gas-quenching fabrication of perovskite films demonstrates promising compatibility for commercialization of perovskite photovoltaics. Seeking suitable ligand for the perovskite precursor inks to improve the crystalline quality of gas-quenched methylammonium free perovskite films is critical for realizing up-scalable fabrication of stable perovskite solar cells. In this work, a series of pyrrolidone-based ligands are employed in gas-quenching fabrication of FA 0.9 Cs 0.1 PbI 3 perovskite films. Optical and morphological characterizations indicate 2-pyrrolidone is the most preferred ligand to deliver a neat buried-interface as well as a light-trapping surface at the rear of the device, which maximized the light-harvesting and the photocurrent of the device. The corresponding device achieved a power conversion efficiency of 21.6% without any interfacial passivation, as well as reduced defect density from their electrical characteristics. Moreover, a more stable performance of the device is obtained with 2-pyrrolidone compared to other pyrrolidone-based ligands, demonstrating 2-pyrrolidone as a promising ligand in designing the perovskite inks for methylammonium-free perovskite solar cells. • Various pyrrolidone-based ligands are studied in gas-quenching of FA 0.9 Cs 0.1 PbI 3 films. • Bifacial optical properties of perovskite films are optimized with NP ligand. • smoother buried interface and a rougher surface contribute to enhanced light harvesting. • NP device achieved 21.6% efficiency without any interfacial passivation [ABSTRACT FROM AUTHOR]