To reduce the cooling and lighting requirements in skyscrapers and increase residential comfort, smart window technologies have been developed to dynamically control the optical transmission of the visible and near-infrared light in the solar spectrum. In this work, we report self-powered electrochromic windows realized by hybridizing enhanced perovskite solar cells. The obtained electrochromic windows, which are powered by tandem solar cells with a voltage of ~2.0 V, exhibit a quick switching time of 9 s and an evident transmittance contrast (~70%) between the colored and bleached states. In practical use, the melting time per unit mass of ice sealed in a glass room could be extended by nearly 20%, exhibiting a good cooling effect. The hybrid system can accelerate the deployment of energy-saving technologies.