Vertical MSM-type CsPbBr₃ thin film photodetectors with fast response speed and low dark current

Abstract

Halide perovskites exhibit excellent electrical and optical properties and are ideal candidates for active layers in optoelectronic devices, especially in the field of high-performance photodetection, where they demonstrate a competitive advantage in terms of development prospects. Among them, the all-inorganic perovskite CsPbBr<sub>3</sub> has received widespread attention due to its better environmental stability. It is demonstrated in this work that a vertical MSM-type CsPbBr<sub>3</sub> thin-film photodetector has characteristics of fast response time and ultra-low dark current. The use of a vertical structure can reduce the transit distance of photo carriers, enabling the device to achieve a fast response time of 63 μs, which is two orders of magnitude higher than the traditional planar MSM-type photodetectors with a response time of 10 ms. Then, by spinning a charge transport layer between the p-type CsPbBr<sub>3</sub> and Ag electrodes, effective separation of photocarriers at the interface is realized and physical passivation between the perovskite and metal electrodes is also achieved. Due to the superior surface quality of the spun TiO<sub>2</sub> film compared with the NiO<sub><i>x</i></sub> film, and through Sentaurus TCAD simulations and bandgap analyses, with TiO<sub>2</sub> serving as the electron transport layer, it effectively inhibits the transmission of excess holes in p-type CsPbBr<sub>3</sub>. Consequently, the electron transport layer TiO<sub>2</sub> is more effective in reducing dark current than the hole transport layer NiO<sub><i>x</i></sub>, with a dark current magnitude of only –4.81×10<sup>–12</sup> A at a –1 V bias. Furthermore, this vertical MSM-type CsPbBr<sub>3</sub> thin-film photodetector also has a large linear dynamic range (122 dB), high detectivity (1.16×10<sup>12</sup> Jones), and good photo-stability. Through Sentaurus TCAD simulation, it is found that the charge transport layer selectively blocks carrier transmission, thereby reducing dark current. The simulation results are in good agreement with experimental data, providing theoretical guidance for a more in-depth understanding of the intrinsic physical mechanisms.