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.

Antisolvent engineering is one of the most widely used methods to obtain high quality perovskite films. This process involves the heavy use of toxic antisolvents, such as toluene (Tol) and chlorobenzene (CB). It is thus highly desirable to develop green antisolvents for the future manufacturing of perovskites. Though several green antisolvents have been developed for iodide perovskites, there are few reports about their application on bromide ones. Besides, the reported green antisolvents for iodide perovskites usually lead to a significant increase in the crystal size, which is not suitable for light emission due to reduced carrier confinement and radiative recombination. Here, we introduce green antisolvent ethyl acetate (EA) to prepare CH3NH3PbBr3 (MAPbBr3) perovskite films. In contrast to previously reported iodide perovskites, EA engineered MAPbBr3 only shows a slight increase in the crystal size. A systematic study on the structural, morphological, and optoelectronic properties of MAPbBr3 prepared with Tol, CB, and EA was carried out. With the benefits of relatively high polarity and low boiling point compared with Tol and CB, EA could extract the solvent more efficiently. This gives rise to MAPbBr3 films with increased crystallinity, improved morphology, and reduced defects, boosting the performance of the corresponding light emitting diodes (LEDs). Our study provides an environmentally friendly way to the manufacturing of efficient MAPbBr3 perovskite LEDs as well as other optoelectronic devices.

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.

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