Designing Surface-Functionalized Ti3C2T2−Cs3

MXene has emerged as one of the frontier two-dimensional materials. In this work, ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{T}_{2}(T=\ensuremath{-}\mathrm{O},\ensuremath{-}\mathrm{Cl},\ensuremath{-}\mathrm{OH}$, or $\ensuremath{-}\mathrm{F})$ MXene-${\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$ perovskite heterostructures are constructed, and the various surface terminations of ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{T}_{2}$ can achieve functionalized perovskite optoelectronic applications in the heterostructures. Lattice-mismatch rates of the ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{T}_{2}$ and ${\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$ heterostructures are only about 1%, which makes the electronic properties of ${\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$ independent of lattice stress in the heterostructures. The binding energies of the ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{T}_{2}/{\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$ interfaces are quite low, especially at the ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}(\mathrm{OH}{)}_{2}/{\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$ interface. Due to the adjustable work function (WF) of ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{T}_{2}$, the types of interface contacts are different, including n- and p-type Schottky contacts and an ohmic contact. The ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}(\mathrm{OH}{)}_{2}/{\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$ interface is an ohmic contact; this is attributed to the big difference in the WFs of ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}(\mathrm{OH}{)}_{2}$ and ${\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$, which could greatly boost the charge-carrier separation and transfer efficiency. In addition, the constructed heterostructures enhance the optical absorption coefficient and reduce charge-carrier effective masses. These results indicate that the ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{T}_{2}/{\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$ heterostructures, especially ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}(\mathrm{OH}{)}_{2}/{\mathrm{Cs}}_{3}{\mathrm{Bi}}_{2}{\mathrm{Br}}_{9}$, can significantly improve the optoelectronic performance of the lead-free perovskite.