Two-dimensional MXene explores ways for applications in perovskite solar cells: A critical review

Perovskite solar cells have been a subject of great interest in photovoltaic research over the past decades due to their high efficiency and low cost. To improve the efficiency and stability performance, as well as lower the cost and complexity for fabrication of perovskite solar cells, careful device design, further material innovation and tailored interface engineering are still needed. Recently, there has been considerable interest in the newly discovered MXenes, a family of two-dimensional transition metal carbides, nitrides and carbonitrides, which have excellent metallic conductivity, abundant surface functional groups, solution processability, tunable work functions, high optical transparency and outstanding mechanical properties, making them promising materials for various applications. With tremendous success achieved, taking together with the strengths of MXene in perovskite solar cells has shown a broad outlook for future application. The explorations of MXene are of great significance for improving the performance and expanding the commercialization of perovskite solar cells, which are still in the early stages. Here, this comprehensive review focuses on the various merits of MXene: as additive in the function layers, as electron transport layers or hole transport layers, as the interface layers, as the electrodes and as multi-roles in sequence, in enhancing the performance and facilitating the application of perovskite solar cells, with the relevant mechanisms behind explained. In detail, the basic properties and production of MXene, and structures of perovskite solar cells are also summarized. With this knowledge, we suggest a broad perspective for designing, preparing, and passivating perovskite solar cells for future innovations by utilizing MXene with high performance.