Tuning the reactivity of PbI2 film via monolayer Ti3C2Tx MXene for two-step-processed CH3NH3PbI3 solar cells

Planar perovskite solar cells prepared by the two-step deposition process possess considerable advantages for the fabrication of high-performance photovoltaic devices. However, the full conversion of the compact PbI 2 in the two-step process to perovskite is highly challenging. In this work, two-dimensional (2D) monolayer Ti 3 C 2 T x (T x = O, OH, and F) MXene nanosheets were first introduced into the PbI 2 layer as a multifunctional additive to enhance the reactivity of PbI 2 by forming porous channels. Such a modification strategy is beneficial for the subsequent reaction with CH 3 NH 3 I (MAI) to completely transform into CH 3 NH 3 PbI 3 (MAPbI 3 ), effectively reducing the amount of the residual PbI 2 in the perovskite film and enlarging the perovskite grain size. Additionally, Ti 3 C 2 T x regulates the work function (WF) of the perovskite, deriving a more ideal energy-level alignment that facilitates carrier extraction and injection. The results also demonstrate that the functional groups on the surface of Ti 3 C 2 T x enable the defects to be passivated by interacting with the under-coordinated Pb 2+ in perovskite, exhibiting a prominent effect on the mitigation of hysteresis as well as suppressing nonradiative recombination. Eventually, a champion power conversion efficiency (PCE) of 19.27% was achieved by introducing 0.03 wt% of the Ti 3 C 2 T x additive, showing an enhancement of ~18% compared to the control devices.