Carbazole-Based\nDual-Band Electrochromic Polymers:\nThe Effect of Linkage Sites on Electrochromic Performance

Dual-band\nelectrochromic (EC) materials are expected to be utilized\nas building materials for energy saving, but their cycle stability\nis still an obstacle. Here, two D–A conjugated polymers, PDPPCz36\nand PDPPCz27, based on diketopyrrolopyrrole and carbazole linked with\ndifferent sites, are synthesized. Both of them exhibit dual-band EC\nbehaviors with a dark blue color in the neutral state and high absorption\nin the near-infrared (NIR) region when oxidized. However, PDPPCz36\nexhibits better cycle stability and a shorter response time than PDPPCz27.\nIn the visible (VIS) region, the PDPPCz36 film exhibits an initial\nlight modulation range (Δ<i>T</i>) of 43.0% and that\nof the PDPPCz27 film is 41.3%. After 100 cycles of redox, the Δ<i>T</i> of the PDPPCz36 film declines by 32%, while that of PDPPCz27\nattenuates by more than 50%. A similar tendency is evident in the\nNIR region. Moreover, PDPPCz36 shows subsecond colored switch times\nboth in the VIS (0.4 s) and NIR (0.7 s) regions, while those of PDPPCz27\nare 2.1 and 1.6 s, respectively. Further research suggests that 3,6-linked\ncarbazoles in PDPPCz36 simultaneously inhibit the side reaction and\nfilm aggregation, which leads to better redox stability and shorter\nresponse time in both EC tests and devices.