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 (Cs₂AgBiBr₆) 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 TiO₂ and Cs₂AgBiBr₆ can effectively promote the transport and extraction of carriers in the device. However, there are few reports on the use of TiO₂ nanopillar arrays as a transport layer to improve the performance of Cs₂AgBiBr₆ photodetectors. In this work, high-quality Cs₂AgBiBr₆ 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 TiO₂ nanopillar arrays are embedded into the Cs₂AgBiBr₆ 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 Cs₂AgBiBr₆ double perovskite photodetectors based on TiO₂ 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/cm², the responsivity is 0.019 A/W and 0.057 A/W, respectively, and the specific detectivity is 1.9 × 10¹⁰ Jones and 5.6 × 10¹⁰ Jones, respectively. Comparing with the Cs₂AgBiBr₆ perovskite photodetector based on a planar TiO₂ 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 Cs₂AgBiBr₆ photodetector is improved by using TiO₂ nanopillars as an electron transport layer. It provides a reference solution for developing high-performance Cs₂AgBiBr₆ perovskite photodetectors in future.