Multi-band response Cs<sub>2</sub>AgBiBr<sub>6</sub> double perovskite photodetector based on TiO<sub>2</sub> nanopillars
Authors: Sun Tang-You , Yu Yan-Li , Qin Zu-Bin , Chen Zan-Hui , Chen Jun-Li , Jiang Yue , Zhang Fa-Bi ,   Guangxi Key Laboratory of Precision Navigation Technology and Application, Guilin University of Electronic Technology, Guilin 541004, China
Published: January 2024

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 from the surface to improve the absorption of incident light in the device and inhibit the 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 work, high-quality Cs<sub>2</sub>AgBiBr<sub>6</sub> thin films with large grain size, no visible pinholes, and good uniform coverage are 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 are 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. When the light source is excited at 365 nm and 405 nm with a light intensity of 0.056 W/cm<sup>2</sup>, the responsivity is 0.019 A/W and 0.057 A/W, respectively, and the specific detectivity is 1.9 × 10<sup>10</sup> Jones and 5.6 × 10<sup>10</sup> Jones, respectively. Comparing with 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 are improved by a factor of 65 and 110, the responsivities are improved by 35% and 256%, and the specific detectivity are improved by a factor of 6.9 and 25, respectively. In this work, the photoelectric performance of Cs<sub>2</sub>AgBiBr<sub>6</sub> photodetector is improved by using TiO<sub>2</sub> nanopillars as an electron transport layer. It provides a reference solution for developing high-performance Cs<sub>2</sub>AgBiBr<sub>6</sub> perovskite photodetectors in future.