Low-Cost Multilayer MXene Doped Carbon Electrode for High-Performance Hole-Transport-Layer-Free Perovskite Solar Cells

Hole-transport-layer (HTL)-free carbon-based PSCs (C-PSCs) show attractive commercial potential due to low production costs, simplifying manufacturing process, and relatively high stability. The defect passivation of perovskite and energy-level modification of the carbon electrode are crucial to further improve the PCE and stability of C-PSCs. Herein, a low-cost multilayer Ti3C2Tx MXene is doped into carbon paste to construct MXene@carbon electrode for C-PSCs. The preparation of multilayer MXene is simple and cost-effective due to only requiring the etching of the MAX phase. The incorporation of MXene appropriately increases the work function, providing a suitable energy level alignment between perovskite and MXene@carbon. The surface Tx groups of MXene can form favorable interaction with the oxygen-containing functional groups of graphite, facilitating the good dispersion of MXene in the carbon paste, which improve the interface contact between perovskite and MXene@carbon and the conductivity and morphology of MXene@carbon electrode. Therefore, the MXene@carbon C-PSCs show enhanced charge transport and extraction and reduced defects and charge recombination and thus achieve significantly improved photovoltaic performance and operational stability. Compared with the conrtol MAPbI3 device with pristine carbon electrode (PCE of 12.69%), the MXene@carbon device exhibits obviously higher PCE of 16.00%, which is top-level for HTL-free MAPbI3 C-PSCs without perovskite passivators. Moreover, the average PCE (14.68%) of the MXene@carbon devices was also significantly higher than that (12.37%) of the control devices. The impressive results indicate the great potential of the MXene doped carbon electrode for high-performance C-PSCs.