Crosslinking strategy effectively enhances stability of ProDOT-based electrochromic polymers and devices under extreme environmental conditions

Electrochromic smart windows regulate environmental temperature by modulating optical transmittance through voltage control, which are applicable to buildings, aircraft, and vehicles. 3,4 - propylenedioxythiophene (ProDOT)-based electrochromic polymers (ECP) are considered highly promising for smart window applications due to chemically tunable multicolor states, fast response, and excellent processability. However, ECP used in smart windows must be weather resistance. 3,4 - propylenedioxythiophene-alt-phenylene yellow copolymer (ECP-Yellow) exhibits wide bandgaps and strong UV absorption, leading to poor stability of the film under solar irradiation. Yet yellow is a primary component in the subtractive CMYK and is critical for expanding ProDOT-based color palettes. This study developed an innovative crosslinking strategy employing a X3DAZP crosslinker. The cycle stability of the crosslinked ECP-Yellow film was increased from 1000 to 3000 cycles. Unencapsulated crosslinked films exhibit 2.3 - and 3 - fold improvements in durability under 85 °C/85 % relative humidity (RH) test and 100-fold intensified light exposure compared to non-crosslinked counterparts. The taupe-tinted material obtained by mixing yellow and magenta ProDOT-based polymers effectively extends the color of the ProDOT system, and the crosslinked film also enhances the durability and cyclic stability. We used ProDOT-based magenta and cyan materials to verify the universality of the crosslinking scheme, and the stability of the electrochromic film was improved. This scheme provides an effective research path for polythiophene-based electrochromic window.