Electrochromic conjugated polymers: The relationship of gradient band gap and electrochromic performance

In the pursuit of high-performance electrochromic materials, in this paper, six donor-acceptor type with different gradient band gaps electrochromic conjugated polymers, named PBTz-T, PBTz-TT, PBTz-DT, PTBTO8-T, PTBTO8-TT, and PTBTO8-DT, were synthesized via direct (hetero) arylation polymerization, employing two benzothiadiazole derivatives with varying electron-accepting capabilities and three thiophene derivatives with different electron-donating capacities. The structures, optical, electrochemical, and electrochromic properties of the six polymers were investigated. As the number of fused thiophene increases, enhancing the electron-donating ability, a growth trend of electrochemical stability is observed for all polymers. Meanwhile, enhance electron-accepting capabilities of acceptors (from benzotriazole to benzothiadiazole) significantly lower the electronic band gap and improve electrochemical stability. PBTz-DT boasts a bleaching time of 0.3 s, outperforming most reported electrochromic polymers. PBTz-T, at 530 nm, exhibits exceptionally high coloration efficiency, reaching 916 cm 2  C⁻ 1 , and demonstrates higher electron utilization and lower energy consumption, making it an excellent candidate for high-performance electrochromic devices. This work compared studies the relationship of gradient band gaps of electrochromic conjugated polymers and their electrochemical and electrochromic performance, offers new insights into enhancing the electrochemical stability and synthesizing high coloration efficiency electrochromic materials.