Cubic structure of the mixed halide perovskite CH3NH3PbI3−xClxvia thermal annealing†
Abstract
A methodology has been developed to obtain a cubic structure of the mixed halide perovskite CH3NH3PbI3−xClx that involves thermal annealing of a vacuum-deposited perovskite layer. In this process, a tetragonal–cubic transition of the mixed halide perovskite CH3NH3PbI3−xClx has been observed using a variety of characterization techniques, e.g., X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical and Hall effect measurements. According to the XRD, the tetragonal structure of CH3NH3PbI3−xClx changed into the cubic phase when the temperature increased to above the transition temperature, at which point all iodine atoms move towards the central axis while PbI6 rotates around the C–N bond. After annealing, the stable cubic structure of the mixed halide perovskite CH3NH3PbI3−xClx has a smaller band gap and a better optical absorption than the original tetragonal structure. Meanwhile, the microstructure has shown an increase of grain size after annealing, which could be given the fastest mobility of 13.5 cm2 V−1 S−1, yielded from the Hall effect measurements. The potential benefits of the stable cubic structure and large grain size in the mixed halide perovskite CH3NH3PbI3−xClx are to improve the device performance of solar cells from the viewpoint of bandgap engineering and crystalline quality.
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