Highly sensitive photoinduced carbon dioxide sensors made using a ZIF-67/Cs2AgBiBr6 heterojunction

Abstract

Carbon dioxide (CO₂) emissions have become a key environmental issue of widespread concern at present. Currently, the use of metal oxide based chem-resistive gas sensors is restricted due to their high operating temperature and short lifetime. Therefore, the development of efficient and rapid gas sensors is of great significance in modern research. A lead-free double perovskite, Cs₂AgBiBr₆ (CABB), can be activated by ultraviolet light and generate a large number of free carriers, which have the potential to increase charge density and enhance the gas sensitivity. Photo-induced carriers provide sufficient reactants, contributing to the interaction between target gases and sensitive semiconductors. A ZIF-67/CABB heterojunction combines gas adsorption by ZIF-67 and photo-activated gas sensing response by CABB in one device, with a response that can reach up to 95.55% when illuminated with 365 nm light and an incident power density of 17.34 mW cm⁻². The average response and recovery times of the ZIF-67/CABB heterojunction can reach 51.54 s and 3.17 s under UV illumination. To achieve the maximum response, the heterojunction devices need to work with the bias of 5 V, which response and recovery times are 60.54 s and 2.68 s, and it is comparable to commercially available CO₂ gas detectors. The heterojunction system decreases the dark current density from 3.89 A m⁻² to 0.78 A m⁻² and also decreases the light current density from 18.48 A m⁻² to 5.33 A m⁻² compared with pristine CABB at a 5 V bias as evidenced by current–voltage characteristic curves, thereby promoting the response and stability of the device. The linear dynamic range of the heterojunction gas sensor is 1700 ppm–14 000 ppm, with a sensitivity of 0.0013% ppm^-1. After more than 35 min of continuous stable operation, the current density remains consistent. This efficient and stable device with a wide operating voltage range represents the future of high-performance photo-induced gas detector applications.