Tunneling-assisted highly sensitive and stable lead-free Cs3Bi2I9 perovskite photodetectors for diffuse reflection imaging

Abstract

Lead-free perovskites exhibit low toxicity and have been investigated as new active materials for photoconversion applications. Among them, Cs₃Bi₂I₉ perovskites have received extensive attention due to their eco-friendliness, excellent stability and high photosensitivity. Herein, the optical and electronic bandgap of Cs₃Bi₂I₉ thin films are determined to be 2.19 eV and 2.55 eV, providing insights into strong excitonic photodetection materials. Furthermore, we introduce an ultrathin Al₂O₃ layer into the interface of Cs₃Bi₂I₉ perovskite PDs using the atomic layer deposition (ALD). The ON/OFF ratio can be significantly improved by 20-fold using an Al₂O₃ layer with an optimal thickness of 1.5 nm due to the interfacial-tunneling-effect. Moreover, the unsealed Cs₃Bi₂I₉ perovskite PDs exhibit excellent stability, and can retain 90% of their original performance after 30 days under ambient conditions (25 °C, RH = 60%). Furthermore, the potential application in diffuse reflection imaging has been explored based on Cs₃Bi₂I₉ perovskite PDs without encapsulation, confirming a high-resolution and high-contrast imaging demonstration.