Multicolored, Low‐Voltage‐Driven, Flexible Organic Electrochromic Devices Based on Oligomers

In this study, a series of organic conjugated oligomers containing 3,4‐ethylenedioxythiophene (EDOT) and aromatic groups are synthesized, which are as follows: 2,5‐di(methyl benzoate)‐3,4‐ethylenedioxy‐thiophene (1EDOT‐2B‐COOCH 3 ), 5,5′‐di(methyl benzoate)‐2,2′‐bi(3,4‐ethylenedioxythiophene) (2EDOT‐2B‐COOCH 3 ), 5,5″‐di(methyl benzoate)‐2,2′:5′,2″‐ter(3,4‐ethylenedioxythiophene) (3EDOT‐2B‐COOCH 3 ), and 5,5″′‐di(methyl benzoate)‐2,2′:5′,2″: 5″,2″′‐quater(3,4‐ethylenedioxythiophene) (4EDOT‐2B‐COOCH 3 ). Using these oligomers as active materials, flexible organic electrochromic devices are fabricated. The device structure is indium tin oxide–PET plastic slide (ITO‐PET)/active layer/conducting gel/ITO‐PET, and the electrochromic properties of oligomers are investigated. These oligomers exhibit reversible color changes upon electrochemical doping and dedoping. The highest optical contrast is exhibited by 4EDOT‐2B‐COOCH 3 , which is 75.2% at 700 nm.