Interfacial interactions of doped-Ti 3 C 2 MXene/MAPbI 3 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 MAPbI 3 WF by hybridizing with fluorine-terminated Ti 3 C 2 T x (F-MXene) and nitrogen-doped Ti 3 C 2 T x (N-MXene). We first reveal the interfacial interaction between MAPbI 3 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 MAPbI 3 /MXene heterostructures using F- and N-MXenes. The F-MXenes extended the most WF of MAPbI 3 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 MAPbI 3 , as demonstrated by PL quenching in MAPbI 3 /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.