Hybrid perovskite solar cells (PSC) are one of the most promising technologies for third-generation photovoltaics due to outstanding semiconductor properties and low-cost solution processing methods for the fabrication[1]. The use of crystallization processes from the liquid phase tends to the formation of defects in the bulk and surfaces that could gain the nonradiative recombination[2]. On the other hand, energy levels (conduction and valence bands, Fermi level) in halide perovskites and charge transporting materials cannot be simply controlled by chemical doping as for Si and AIIIBV semiconductors. The use of interface engineering for micro-grain perovskite films and heterojunction of the PSC was demonstrated as an efficient tool for the passivation of traps and energy level alignment. Recently, a new class of 2D materials – Mxenes (M_n+1X_nT_x, where M represents transition metal, X is carbon or nitrogen, and T_x shows functional termination (OH, O or F, etc.)) was considered as promising material for tuning the surface properties in PSC due unique tunability of work function values (from of 1.6 to 6.5 eV w). Several reports showed impressive results for the gain in PCE(20+%)[3], [4] and the shifting of the work function in perovskite absorber and ETL for n-i-p structures of PCSs[4].

In this work, we demonstrate the beneficial results for the application of Ti₃C₂T_x MXenes (MX) in the structure of an inverted planar perovskite solar cell. The output characteristics of the fabricated devices (ITO/NiO/perovskite/PCBM/BCP/Ag) were significantly improved with direct correlation to the presence of MXenes in perovskite absorber or ETL. The reference devices showed an average level of PCE ~17 %, and incorporation of MX absorber and ETL films increased efficiency up to >19%. We assume that energy level shifting with the incorporation of MX should be done in parallel for perovskite and ETL to provide more favorable alignment of the conduction band position. For PSCs with MX in absorber and ETL, the improvement mainly manifested in the increment of Jsc, confirmed by higher EQE level in the near-infrared region, which represents the quality of electron collection. We found that perovskite films with MX showed gain of the PL without shifting of the peak that corresponds to the passivation of grain boundaries.

This work shows the universality of Mxenes application in the structure of perovskite solar cells with fine tuning of properties and promising way for further optimization of PCS operation with incorporation of the 2D materials.