Photolithographically patterned and highly stable electrochromic displays enabled by a photo-assisted cross-linker

Photolithography is a standard technique for high resolution patterning of electronic devices. This study presents a new tris-diazo compound (X8) as a carbene crosslinker which responds to UV photons and can be directly patterned by photolithography. The tris-diazo compound (X8) has been successfully applied to fabricate solution-processable electrochromic polymer (ECP) displays. Upon exposure to UV light of 254 nm wavelength, the blend of X8 (≤5 wt%) with ECP (PProDOT, poly(3,4-propylenedioxythiophene)) can cross-link, exhibiting a ∼93% solvent resistance whereas the pristine PProDOT does not cross-link at all. The electrochromic devices (ECDs) based on the crosslinked PProDOT showed an exceptional stability of 300 000 operational cycles, with both bleaching and coloring time of 0.5 s without obvious deterioration. With lithographical patterning, a minimum 50 μm size of display pixel has been realized, which paves the way for future large-area and low-cost electrochromic display applications.