Photovoltaic self-powered gas sensors are generally based on the device structure of a p–n photodiode, which requires two different electrodes on opposite sides of a heterojunction. However, the complicated structure is not compatible with planar circuit technology. A strategy of applying the lateral photovoltaic effect in detecting ozone (O₃) is proposed. By using asymmetric light illumination, self-powering operation is achieved without an external voltage. The recorded unbiased gas response is 88.6%, with a response/recovery time of 150/800 s after exposure to 5 ppm O₃ at room temperature. The Cu₂O self-powered gas sensor has excellent selectivity to toxic gases, reliability under humidity and long-term stability to O₃. This study could provide new insights in the self-powered device domain.