CO2 sensors capable of operating at room temperature were fabricated using LaOCl/SnO2 thin films. The carrier mobility of the SnO2 layer was increased by H2 ambient annealing, during which the O vacancies in SnO2 were passivated by H atoms. The sensitivity of the CO2 sensors was strongly affected by the mobility of the SnO2 layer because of the large diffusion length of carriers. By using the SnO2 layer with a carrier mobility of 10.6 cm2 V−1 s−1, a highly sensitive CO2 sensor with a detection limit of 1000 ppm was obtained. The sensor was visible-light-transparent and the transmittance in the visible region was over 70%.

Monolithic visible‐light‐transparent carbon dioxide (CO2) sensor/solar cell‐integrated devices are fabricated using RF sputtering. The optical transmittance of the integrated device in the visible region is found to be over 60%. The solar cell is composed of p‐type NiO and n‐type ZnO layers, and exhibits small but noticeable photovoltaic effect under illumination. The CO2 sensor layer is made from LaOCl/SnO2 layers, and its resistance varies when electrical power is supplied from an external power source. XPS measurement reveals that adsorbed oxygen, which influences the sensitivity of gas sensors, increases with increasing LaOCl catalyst concentration. The results of this study can serve as a first step toward achieving a new type of visible‐light‐transparent CO2 sensor/UV absorbed solar cell for integrated self‐powered devices.

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