Recently, SnO2 has been recognized as a promising electron transport layer (ETL) for perovskite solar cells (PSCs) due to its outstanding optoelectronic properties and low-temperature fabricating process. However, the detrimental defects formed at the SnO2/perovskite interface and within bulk perovskite films cause severe non-radiative recombination, limiting the further improvement of power conversion efficiencies (PCEs). Herein, we have demonstrated a facile surface treatment on SnO2 through KF modification to passivate defects at both regions simultaneously. F– ions reduce the detrimental hydroxyl group defects on the SnO2 surface effectively, resulting in improved crystallinity of perovskite films with a more favorable morphology. Meanwhile, a preferred energy level alignment between SnO2 and MAPbI3 films is obtained, improving the carrier transport capability. Moreover, K+ ions can diffuse into the MAPbI3 film, passivating the grain boundaries and intrinsic I– vacancy defects. Consequently, a significant increase in PCE from 18.47 to 20.33% is achieved for a MAPbI3 PSC based on a SnO2/KF ETL, with negligible hysteresis and improved stability.

Solution-processed organic/inorganic hybrid halide perovskites are a class of very promising photovoltaic materials because of their extraordinary optoelectronic properties. However, numerous intrinsic defects within perovskite films limit the performance enhancement of perovskite solar cells (PSCs). Herein, we introduce three different alkali metal fluoride additives into the perovskite precursor to modulate the defect behaviors. The addition of alkali metal fluorides, especially potassium fluoride (KF), significantly passivates grain boundaries and point defects within bulk perovskite films, contributing to increased carrier lifetime and reduced defect state density. By optimizing the concentration of additives, the PSC device with 1% KF added has realized a significantly enhanced power conversion efficiency of 20.11%, and ignorable hysteresis.

The performance improvement of perovskite solar cells (PSCs) is strongly limited by the defects generated at the carrier transport layers/perovskite interface. Due to the complexity of intrinsic defects occurring in both SnO2 and perovskite layers, the introduction of appropriate multifunctional passivating molecules or groups is of great interest to suppress the defects at the interface of SnO2/perovskite. In this work, a facile way to simultaneously passivate the defects at both the surface of SnO2 and the bottom surface of the perovskite layer has been proposed using an interlayer of 3-chlorothiophene-2-carboxylic acid (TCA-Cl). Carboxylic acid in TCA-Cl can form a chemical linker between SnO2 and perovskite via an esterification, leading to the reduction of surface hydroxyl group defects of SnO2. The S, −COO–, and −Cl can modulate the surface electronic states of SnO2 and strengthen the binding at the interface of SnO2/perovskite, and moreover, they passivate the iodine vacancies (V I +) and undercoordinated Pb2+ defects on the surface of perovskite films. Besides, the energy-level alignment is very well modulated by the strong binder of TCA-Cl, leading to the improved carrier extraction at the interface of SnO2/perovskite. As a result, the conversion efficiency of MAPbI3 PSCs achieves up to 21.07% (18.41% for the control), with decreased hysteresis and increased stability.

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