A photo rechargeable capacitor based on the p–n heterojunction of ZnO/ZIF-67 showing enhanced photovoltage

Abstract

The photo rechargeable device (PRD) has been continuously drawing attention because it combines energy conversion and storage in one device. As for the photoelectrode of PRD, the construction of heterojunction is of crucial importance to enhance the photo performance. In this work, a two-electrode photo rechargeable capacitor based on the p–n heterojunction of ZnO/ZIF-67 is fabricated. ZIF-67 not only serves as the energy storage material but also forms the p–n heterojunction together with ZnO. A fast volatilization method was adopted for the in situ growth of ZIF-67 on ZnO nanorods to ensure sufficient mass loading and fewer interface defects. The results show a photovoltage of 0.36 V (0.2 V higher than single ZnO), a specific capacitance of 759.0 mF/g, and an overall energy conversion efficiency of 0.49%. The enhanced photovoltage is attributed to the p–n heterojunction. Moreover, a practical button cell was also fabricated, with 91% Coulombic efficiency remaining after 3000 cycles in the dark.