Dibenzofuran/dibenzothiophene and carbazole based conjugated polymers for green building radiative cooling with the color changing from colorless to dark blue

Electrochromic smart windows (ECSWs) have emerged as an important solution for dynamically regulating solar radiation of buildings. However, the high optical contrast from the colorless to dark state and the optimization of a range of parameters have limited the development of ECSW materials. Herein, a series of conjugated polymers from DBT/DBF and Cz were designed (named DBT-Cz-6C, DBF-Cz-6C, DBT-Cz-Ph and DBF-Cz-Ph), which exhibit not only improved structural stability but also a broadened electrochromic color tuning range. All four conjugated polymers exhibit excellent electrochemical performance and the color can change from colorless to dark blue. In particular, DBT-Cz-6C achieves an initial maximum transmittance of 90% with only 5% loss in transmittance after 1000 cycles. DBT-Cz-6C was further fabricated into an electrochromic device (ECD) for further research. After 400 testing cycles, the transmittance of the DBT-Cz-6C ECD only decreased by 2%, and the coloring time and bleaching time were 4.5 s and 4.9 s, respectively. Subsequently, the thermal management performance of the DBT-Cz-6C ECD was simulated using EnergyPlus. Building models covering 20 cities across diverse climate zones in China show that buildings equipped with DBT-Cz-6C ECSWs achieve annual energy savings ranging from 13.1% to 25.7%. The ECSW incorporating the DBT-Cz-6C conjugated polymer effectively reduces the cooling-system load and demonstrates significant energy savings by dynamically regulating solar radiation. Overall, this work implies the great potential of these conjugated polymers in low-carbon buildings.