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

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.