Diamond, Graphite & Carbon Materials

We present an electrochromic device (ECD) fabricated using PEDOT:PSS and graphene as active conductive electrode films and a flexible compliant polyurethane substrate with 1-ethyl-3-methylimidazolium bis(trifl uoromethylsulfonyl) imide (EMI-TSFI) additive, as ionic medium. This device with a docile, elastic intermediate substrate along with a transparency controlled PEDOT: PSS film provides a wide color contrast and fast switching rate. We harness wrinkling instability of graphene to achieve a hydrophobic nature without compromising transparency of the ECD. This mechanical self-assembly approach helps in controlling the wavelength of wrinkles generated by inducing measured prestrain conditions and regulating the modulus contrast by selection of underlying materials used, thereby controlling the extent of transparency. The reduction and oxidation switching times for the device were analyzed to be 5.76 s and 5.34 s for a 90% transmittance change at an operating

DC voltage of 15 ± 0.1 V. Strain-dependent studies shows that the performance was robust with the device retaining switching contrasts even at 15% uniaxial strain conditions. Our device also exhibits superior anti-wetting properties with an average water contact angle of 110° ± 2° at an induced radial prestrain of 30% in the graphene film. A wide range color contrast, flexibility, and anti-wetting nature of the device envision its uses in smart windows, visors, and other wearable equipment where these functionalities are of utmost importance for developing a new generation of smart interactive devices.