Recent Development of Transparent Conducting Oxide-Free Flexible Thin-Film Solar Cells

The rapid development of the modern electronics gives rise to higher demands of flexible and wearable energy resources. Flexible transparent conducting electrodes (TCEs) are one of the essential components for flexible/wearable thin-film solar cells (SCs). In this regard, commercial indium tin oxide (ITO) on plastics has demonstrated superior optoelectronic performance although some drawbacks, i.e., the low abundance, film brittleness, low infrared transmittance, and poor chemical stability remain. On the other hand, several other transparent conducting oxide (TCO)-free transparent conductive materials, such as carbon nanotubes (CNTs), graphene, metallic nanowires (NWs), and conducting polymers, have experienced a rapid development to address these issues. In this feature article, an overview over the latest development of several flexible TCO-free thin film SCs, i.e., organic solar cells (OSCs), dye-sensitized solar cells (DSSCs), perovskite solar cells (pero-SCs), and fiber/wire-shaped SCs is provided. Three groups of flexible TCO-free thin film solar cells can be categorized according to their configurations: (i) front-side illuminated planar configuration; (ii) back-side illuminated planar configuration, and (iii) fiber-shaped solar cells (FSSCs). The article is focused on flexible TCO-free TCEs, including CNTs, graphene, metallic NW/nanotroughs, metallic grids, conducting polymers, metallic fiber, and carbon based fibers.