Current progress in interfacial engineering of carbon-based perovskite solar cells

Using carbon paste as the back electrode for perovskite solar cells (C-PSCs) has attracted significant attention due to their low cost and excellent stability. In general, the device structure of the fabricated C-PSCs is hole transport layer (HTL) free, and the carbon paste electrodes (CPEs) could directly collect the photo-generated holes. Therefore, interfacial engineering between the perovskite and CPE plays a crucial role in charge collection and affects the performance of C-PSCs. Many studies have been carried out in interfacial engineering so far; however, no review has summarized the work done in this field. Herein, we summarize the continuing progress in interfacial engineering of C-PSCs. Two kinds of contacts have been defined due to the different interfacial contacts in C-PSCs: bi-interfacial and tri-interfacial structures. Techniques for the fabrication of perovskite layers, CPEs, and insulating layers have been discussed for each structure, including the main issues and solutions. Finally, conclusions and perspectives are provided for the future designs and development of C-PSCs.