Indoor photovoltaic is one of the most important applications of organic solar cells (OSCs). As different from AM1.5G sunlight with broad spectra from the visible to near‐infrared region, the spectra of indoor light are usually located in the visible region. Therefore, a special material design for the photoactive layer to meet the requirement of indoor light is required for application in indoor photovoltaics. Herein, a wide‐bandgap double‐cable conjugated polymer is intentionally selected, which has the well‐matched absorption spectra with indoor light for use in indoor OSCs. This double‐cable polymer is used as a single photoactive layer in OSCs, providing a high power conversion efficiency of 19.44% under indoor light, which is comparable with the bulk‐heterojunction solar cells using near‐infrared electron acceptors. Moreover, the double‐cable polymer‐based indoor OSCs exhibit high storage stability. These results indicate that single‐component OSCs based on double‐cable polymers have promising applications in indoor OSCs.