Fabrication of solar cells with CO ₂ gas sensing capabilities based on a NiO/ZnO p-n junction for developing self-powered gas sensors

Solar cells based on a NiO/ZnO p-n junction structure responding to CO 2 gas were fabricated by conventional RF sputtering. The developed NiO/ZnO solar cells exhibited evident photovoltaic effects and response to CO 2 gas when exposed to sunlight at room temperature without thermal heating or external power supply. The open-circuit voltage, generated by the solar cells absorbing only UV light, increased in a CO 2 atmosphere and decreased in air. Moreover, the response mechanism of the NiO/ZnO solar cells to CO 2 gas was investigated using electrochemical impedance spectroscopy. The results suggested that the depletion layer width of the NiO/ZnO interface changed under CO 2 gas with light illumination. These results represent the potential application of the NiO/ZnO p-n junction structure toward self-powered gas sensors.