Two-step spin coating CsPbBr3 thin films and photodetectors in the atmosphere.

Recently, inorganic halide perovskites, especially CsPbBr3, have been attracting attention because of their high efficiency, wide color gamut, and narrow luminescent spectrum. To elevate the perovskite devices' performance, optimizations of crystalline quality, device structures, and fabrication process are essential. Currently, the state-of-the-art fabrication approach of CsPbBr3 is spin-coating in an inert environment (nitrogen, argon, etc.), which requires temperature and humidity control. In this work, a CsPbBr3-based visible photodetector (PD) is realized in a humid atmosphere, whose performances were comparable to those reported in an inert glovebox. The dependencies of responsivity and transient time on CsBr coating layer numbers and electrode period were also investigated. The best device performance was obtained with 4 layers of CsBr coating with a responsivity of 107.2 mA/W, detectivity of 4.29 × 1010 Jones, and quantum efficiency of 25.4%. The rise time of the 3-4-layer CsBr-coated PD was reduced by the higher crystalline quality and carrier mobility, while the decay time of the 1-layer CsBr-coated PD was faster since the dense defect induced non-radiative recombination centers. With the period T increasing, the responsivity decreased, while the transient times increased. We believe that our results could benefit the future optimization of perovskite materials and PDs.

Investigation of CsPbBr3 CVD dynamics at various temperatures.

Since the emerging development of CsPbBr3 perovskite, chemical vapor deposition (CVD) has become one of the most promising fabrication techniques by which to precisely deposit uniform perovskite thin films. However, there have been few reports on the growth dynamics and chemical reaction parameters (e.g., activation energy) for perovskite CVD. In this work, different deposition rates of CVD-grown CsPbBr3 thin films were obtained at different substrate temperatures. Dynamics equations were developed to relate the inflow rates, desorption coefficients and concentrations of reactants on the substrates. Only a small amount of reactant became activated at low temperature and a small amount of PbBr2 resided on the substrate at high temperature, and accordingly the maximal deposition rate was achieved at 250 °C. The Arrhenius activation energy of CVD-grown CsPbBr3 was also calculated, and found to be 31.64 kJ mol-1. We believe that our work provides a detailed picture of perovskite CVD growth.