Enhanced perovskite phototransistor by multi-step slow annealing strategy

Methylammonium lead halide perovskites have received substantial attention in the research photovoltaic communities, because of excellent optoelectronic properties, including long electron-hole diffusion distance, large absorption coefficients in the UV-Vis spectral region, low-cost, solution-based processing and low binding energy of exciton. However, the crystal defects of perovskite films such as pinholes, defect and grain boundaries lead to carrier capture, trapping and scattering, so that reduce carrier mobility in the channel, which has become the bottleneck of high device performance and limited the application in photo detection. Here we report a simple and straightforward strategy based on a multi-step annealing process, which can effectively improves the coverage, smoothness, uniformity and crystallinity by restraining defects of pinhole formation. The field-effect mobilities of perovskite photodetector treated by one-step (OS) direct annealing method at room temperature shows mobility as 0.256 (0.129) cm2V−1s−1 for holes (electrons), which increase to 2.32 (1.18) cm2V−1s−1 for that treated by muti-step (MS) annealing method. The latter exhibits high figure of merit as detectivity of 8.94 × 1011 Jones, a responsivity of 32 A/W and a short response time of 42 μs . Moreover, it shows better stability with polymethylmethacrylate film covered, which can maintain 90% of initial performance for 10 days in ambient air. These findings demonstrate that MS annealing methods is simple yet effective and feasible to prepared high-efficient perovskite based photo detectors.