An effective modulation of bulk perovskite by V₂CT_x nanosheets for efficient planar perovskite solar cells

Crystallization modulation and defect passivation are key for high performance perovskite solar cells (PSCs) through suppressing defects in the surface and/or near the grain boundaries (GBs) of solution-processed perovskite films. In this work, we report simultaneous modulation of crystallization and passivation of defects for perovskites through a new vanadium carbide (V₂CT_x) MXene that is employed in an anti-solvent. The final modified perovskite film showed an improved crystallization, better energy level alignment and higher hole injection with a hole-transporting layer, leading to an increased power conversion efficiency from 20.1% up to 23.47% for planar PSCs, with enhanced device stability retaining over 90% of the initial PCE after 1000 hours exposure under 40-60% relative humidity at 25 °C. We have further employed the synchrotron radiation in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) equipment to monitor the kinetic process of crystallization during spin-coating; it is notable that a lower dimensional perovskite structure (n < 3) was observed in the modified perovskite film during the process of dropping the antisolvent CB with V₂CT_x, which helps explain the enhanced device stability.