Insights into the application of carbon materials in heterojunction solar cells

The design of carbon material-based heterojunction solar cells (HJSCs) provides a promising approach to convert and collect solar energy. With unique photonic, electronic and mechanical properties, versatile carbon materials have attracted considerable attention in the design of heterojunction structures because of the multi-functional applications of carbon materials in the booming field of photovoltaics (PVs). Significant effort has been devoted to enhancing the light absorption capacity and charge/carrier transporting ability to obtain state-of-the-art HJSCs. This review presents the basic application of various carbon materials for PVs and the basic principles of carbon materials in HJSCs. Several optimisation methods for carbon nanotube (CNT) film modification and cell performance, such as optical property and Fermi level tuning, as well as morphological design and interface engineering, are highlighted in a summary of the state-of-art progress of CNT-based HJSCs. Moreover, the representative applications of carbon materials based flexible HJSCs are discussed. Finally, promising pathways and prospects of CNTs in HJSCs and their advanced devices are proposed using film modification, mechanism modulation, and device design to achieve cost-effective, high-performance, and flexible solar cells (SCs).