Past achievements and future challenges in the development of optically transparent electrodes

Transparent conductive electrodes play important roles in information and energy technologies. These materials, particularly transparent conductive oxides, are widely used as transparent electrodes across technical fields such as low-emissivity coatings, flat-panel displays, thin-film solar cells and organic light-emitting diodes. This Review begins by summarizing the properties and applications of transparent conductive oxides such as In2O3, SnO2, ZnO and TiO2. Owing to the increasing demand for raw materials - especially indium - scientists are currently searching for alternatives to indium tin oxide. Carbon nanotube and metal nanowire networks, as well as regular metal grids, have been investigated for use as transparent conductive electrodes. This Review compares these materials and the recently 'rediscovered' graphene with today's established transparent conductive oxides.