Multi-band response Cs₂AgBiBr₆ double perovskite photodetector based on TiO₂ nanopillars

Abstract

Photodetectors are widely used in the fields of environmental monitoring, medical analysis, security surveillance, optical communication and biosensing due to their high responsiveness, fast response time, low power consumption, good stability and low processing cost. Fully inorganic lead-free perovskite material (Cs<sub>2</sub>AgBiBr<sub>6</sub>) has received a lot of attention in recent years in the research of photodetector applications due to its advantages of long carrier lifetime, high stability, moderate forbidden bandwidth, and environmental friendliness. For perovskite photodetectors, the semiconductor nanopillar array structure can effectively reduce the reflection loss of light on the surface to improve the absorption of incident light in the device and inhibit the dynamics of exciton complexes in the device, and the good energy level matching between TiO<sub>2</sub> and Cs<sub>2</sub>AgBiBr<sub>6</sub> can effectively promote the transport and extraction of carriers in the device. However, there are few reports on the use of TiO<sub>2</sub> nanopillar arrays as a transport layer to improve the performance of Cs<sub>2</sub>AgBiBr<sub>6</sub> photodetectors. In this paper, high-quality Cs<sub>2</sub>AgBiBr<sub>6</sub> thin films with large grain size, no visible pinholes and good uniform coverage were successfully prepared by a low-pressure-assisted spin-coating method under ambient conditions. Hydrothermally grown TiO<sub>2</sub> nanopillar arrays are embedded into the Cs<sub>2</sub>AgBiBr<sub>6</sub> layer to form a close core-shell structure, increasing the physical contact area between the two to ensure more effective electron injection and charge separation, and to improve the carrier transport efficiency in the device. Multi-band responsive Cs<sub>2</sub>AgBiBr<sub>6</sub> double perovskite photodetectors based on TiO<sub>2</sub> nanopillars were excited at multiple wavelengths of 365 nm and 405 nm with high light response and good stability and reproducibility, resulting in average switching ratios of 522 and 2090, respectively. Excitation of the light source at 365 nm and 405 nm with a light intensity of 0.056 W/cm<sup>2</sup> resulted in responsivity of 0.019 A/W and 0.057 A/W, with specific detectivity of 1.9 × 10<sup>10</sup> Jones and 5.6 × 10<sup>10</sup> Jones, respectively. Compared to the Cs<sub>2</sub>AgBiBr<sub>6</sub> perovskite photodetector based on a planar TiO<sub>2</sub> electron transport layer, the average switching ratios have been improved by a factor of 65 and 110, the responsivities have been improved by 35 per and 256 per, and the specific detectivity have been improved by a factor of 6.9 and 25, respectively. In this paper, the photoelectric performance of Cs<sub>2</sub>AgBiBr<sub>6</sub> photodetectors was improved by using TiO<sub>2</sub> nanopillars as electron transport layer. It provides a reference solution for the future development of high-performance Cs<sub>2</sub>AgBiBr<sub>6</sub> perovskite photodetectors.