All-Solid-State Transparent-to-Black Electrochromic Smart Window for Building Energy Saving

All-solid-state electrochromic devices (ECDs) demonstrate significant potential for smart window applications through the voltage-regulated modulation of solar radiation transmittance. Current implementations remain constrained by insufficient optical contrast, resulting in suboptimal solar heat gain coefficients. In this study, we present a molecular engineering approach utilizing p-terphenyl to develop transparent-to-blank transmissive electrochromic polymers (ECPs) with enhanced optical performance, creating ECDs with decent optical contrast and switching speed. Structural modification through terphenyl incorporation induces substantial bandgap enlargement in the polymeric system, thereby enhancing optical transparency in the neutral state. The optimized PTPA-TP derivatives exhibit superior performance characteristics, achieving an integrated optical contrast ratio of 88.2% across the visible spectrum with peak modulation of 90.6% at 508 nm. Notably, the device demonstrates exceptional switching kinetics with coloration and bleaching times of 1.6 and 2.0 s, respectively, resulting from expanded interplanar spacing that facilitates efficient ion transport. In simulations assessing building energy savings, the PTPA-TP smart window is projected to save between 9.8% and 16.6% of the total annual energy in nine cities with diverse climates, with a notable saving of 5.97 kWh per year in Xiamen. These findings underscore the potential for PTPA-TP as a promising candidate for next-generation electrochromic smart windows, paving the way for energy-efficient and sustainable building designs.