Anion exchange of halide perovskites can be a practical pathway for optoelectronic properties. In general, the deterioration of morphology, incomplete anion exchange, and harsh reaction conditions are critical issues in exploring devices. Because of the poor stability of organic-inorganic halide perovskite materials in humid conditions, the successful applications of perovskite solar cells are hindered.Indeed, requiring a controlled atmosphere for device fabrication and operation is a disadvantage of this process. In this study, attempts have been made to study bromide exchange to chloride at room temperature. First, a tiny droplet of MAPbCl3 precursor solution was manually placed onto centimeter-scale MAPbBr3 single crystalline (SC) thin film samples via disposable glass micropipettes with a minimal volume. The droplet was placed arbitrarily in the center of the CH3NH3PbBr3 thin film under spatially confined growth conditions. Then, a home-built microscope was used to monitor chemical reactions (Field of view of AC254-075-AB Lens = 1.91mm*1.43mm) for a prolonged duration under ambient conditions. Based on time-lapse imaging of MAPbBr3 thin films, it was observed that the Cl/Br exchange occurs via the appearance of a new phase (yellow cubic crystals) and the concomitant disappearance of the starting one (MAPbBr3). In fact, it would assume that, at ambient temperature, the halide substitution in the MAPbBr3 single crystalline thin films, followed by a hydrophobic treatment of the substrate, is rapid and experiences different phases within minutes after contact with MAPbCl3. In addition, the precursor solution of MAPbCl3 (1) containing DMSO (dimethyl sulfoxide, and DMF (dimethyl formamide) might react with MAPbBr3 thin films and begin dissolvation of the MAPbBr3 single crystalline perovskite materials. Subsequently, MAPbBr3 thin films are converted into the intermediate phase (2), forming new black cubic crystals (3). Exceptions were also visualized for bromide conversation by MAPbI3 precursor solution.

Fast halide exchange of Cl/Br co-insertion into the perovskite lattice thin films at room temperature

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