Hole-transporting materials boost optoelectronic performance: Their first application in electrochromic device based on 1,1′-Bis(3-sulfopropyl) viologen

In this paper, we present the first application of organic hole-transporting semiconductors 4,4′,4′'-tris(carbazol-9-yl)triphenylamine (TCTA) and 4,4′-cyclohexylbis[N,N-bis(4-methylphenyl) aniline] (TAPC) in electrochromism area, demonstrating that TCTA or TAPC is suitable for use as hole-transporting materials on the anode of 1,1′-bis(3-sulfopropyl) viologen (SPV)-based electrochromic devices. For such devices, we obtain a decreased driving voltage of SPV-based electrochromic devices down to −2.0 V in the presence of TCTA or TAPC with comparison to that of ca. −2.5 V in the absence of the hole-transporting material. The optical contrast of the device increased from 57.19 % (without hole-transport layer) to 66.41 % (TCTA) or 62.97 % (TAPC) at 533 nm. The response time of 66.2 s in the absence of hole-transporting layer can decrease to 30.6 s with TCTA and 62.7 s with TAPC, respectively. The coloration efficiency of the as-fabricated devices at 533 nm can reach from 67.3 cm²/C (SPV-only) up to 153.2 cm²/C (TCTA) and 80.5 cm²/C (TAPC). This work paved a new way for boosting electrochromic performances of viologen-based devices via electrode modification of anode by hole-transporting material TCTA and TAPC which have been used effectively and efficiently in organic electroluminescent devices and solar cells.