Nano-branched transparent conducting oxides: beyond the brittleness limit for flexible electrode applicationsElectronic supplementary information (ESI) available. See DOI: 10.1039/c2nr32228e

Although the performance of transparent conducting oxides based on bixbyite In 2 O 3 (Sn doped In 2 O 3 : ITO) and wurtzite ZnO (Al, In, and Ga doped ZnO) is sufficient in conventional optoelectronic devices, their flexibility remains insufficient for demands in mobile and foldable electronics generation. A lot of alternative materials such as metallic nanowires and carbon based nano-structures have been tried for transparent flexible electrodes, but poor thermal stability of metal nanowires and limits in conductivity of carbon based nano-structures are still waiting for permanent solutions. Here, we show that the cross-linked ITO nano-branches have superior mechanical flexibility compared to ITO bulk film without any cracks even with a bending radius of 0.1 cm. Moreover, for equivalent sheet resistivity, the ITO nano-branches exhibit optical transmittance comparable to that of commercial metallic nanowires (such as Ag and Cu in the visible spectrum) but show far superior thermal stability in conductivity without any degradation even at a temperature of 200 °C and a humidity of 90%. Cross-linked ITO nano-branches with high conductivity and transparency have superior mechanical flexibility compared to bulk ITO film without any cracks.