Anhydrous organic etching derived fluorine-rich terminated MXene nanosheets for efficient and stable perovskite solar cells

MXene have exhibited their potential in the perovskite photovoltaic domain. Nevertheless, the majority of studies mainly focus on the profits of regular hydrophilic Ti3C2Tx on charge transport and energy level regulation, lacking a reasonable design on the surface chemistry aimed at the long-term stability of perovskite solar cells (PSCs). Herein, we report a novel anhydrous etching strategy to synthesize fluorine-rich and hydroxyl-free terminated Ti3C2Tx as an additive of perovskite. The tailored hydrophobic nanosheets are distributed at grain boundaries (GBs), in which Ti3C2 constructs a conductive network to promote the flow of carrier, and the bilateral terminal groups take multi-protected roles. Abundant F groups repel the attack of external moisture on GBs, and the internal perovskite lattice is immobilized and passivated by electronegative F and O through hydrogen bond and electrostatic interaction. The target CsFAMA-based PSCs yield a champion power conversion efficiency (PCE) of 21.52% and a negligible J-V hysteresis. The unencapsulated devices perform superior stability to humidity, thermal, and illumination, retaining 80 - 90% of the initial efficiency after - 1000 h. Such MXene with novel surface groups presents superiority over conventional MXene in terms of improving both PCE and comprehensive stability. This work unveils the significance of well-tuned MXene for PSCs to balance efficiency and stability and paves an avenue for versatile MXene to be applied to broader fields.