Interfacial interactions of doped-Ti₃C₂ MXene/MAPbI₃ heterostructures: surfaces and the theoretical approach

The work function (WF) of perovskite materials is essential for developing optoelectronic devices enabling efficient charge transfer at their interfaces. Perovskite's WF can be tuned by MXenes, a new class of two-dimensional (2D) early transition metal carbides, nitrides, and carbonitrides. Their variable surface terminations or the possibility of introducing elemental dopants could advance perovskites. However, the influence of doped-MXenes on perovskite materials is still not fully understood and elaborated. This study provides mechanistic insight into verifying the tunability of MAPbI₃ WF by hybridizing with fluorine-terminated Ti₃C₂T (F-MXene) and nitrogen-doped Ti₃C₂T (N-MXene). We first reveal the interfacial interaction between MAPbI₃ and MXenes via X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and photoluminescence spectroscopy (PL). UPS supported by density functional theory (DFT) calculations allowed the description of the influence of F and N on MXene's WF. Furthermore, we developed MAPbI₃/MXene heterostructures using F- and N-MXenes. The F-MXenes extended the most WF of MAPbI₃ from 4.50 eV up to 3.00 eV, compared to only a small shift for N-MXene. The underlying mechanism was charge transfer from low WF F-MXene to MAPbI₃, as demonstrated by PL quenching in MAPbI₃/F-MXene heterostructures. Altogether, this work showcases the potential of fluorine-doped MXenes over nitrogen-doped MXenes in advancing perovskite heterostructures, thus opening a door for efficient optoelectronic devices.