Titanium-carbide MXenes for work function and interface engineering in perovskite solar cells

To improve the efficiency of perovskite solar cells, careful device design and tailored interface engineering are needed to enhance optoelectronic properties and the charge extraction process at the selective electrodes. Here, we use two-dimensional transition metal carbides (MXene Ti₃C₂T_x) with various termination groups (T_x) to tune the work function (WF) of the perovskite absorber and the TiO₂ electron transport layer (ETL), and to engineer the perovskite/ETL interface. Ultraviolet photoemission spectroscopy measurements and density functional theory calculations show that the addition of Ti₃C₂T_x to halide perovskite and TiO₂ layers permits the tuning of the materials' WFs without affecting other electronic properties. Moreover, the dipole induced by the Ti₃C₂T_x at the perovskite/ETL interface can be used to change the band alignment between these layers. The combined action of WF tuning and interface engineering can lead to substantial performance improvements in MXene-modified perovskite solar cells, as shown by the 26% increase of power conversion efficiency and hysteresis reduction with respect to reference cells without MXene.