The Search for Alternatives:

Indium-free transparent oxides do exist, but supply bottlenecks are becoming more frequent due to increasing demand. Furthermore, fundamental disadvantages such as brittleness and deformation remain an issue. As a result, alternative transparent conductive coatings are being researched intensely, examples being conductive polymers, carbon nanotubes and graphenes. Carbon based electrodes, however, generally have an excessively high surface resistance and thus are insufficiently conductive. If a metallic grid is integrated into an organic layer, the resistance drops, but so does the mechanical

stability; if a solar cell produced by this method were to be bent, the layers would break and loose their conductivity. The challenge thus consists of manufacturing flexible yet stable conductive substrates, ideally in a cost-effective industrial roll-to-roll process.