Controlling the Defect Density of Perovskite Films by MXene/SnO₂Hybrid Electron Transport Layers for Efficient and Stable Photovoltaics

The defect control of polycrystalline perovskite films is essential for achieving an efficient and stable perovskite solar cell (PSC). However, existing methods of reducing defects suffer from their complex processes, low durability, and limited effects by using molecular materials in terms of passivation mechanisms. Herein, a hybrid film composed of SnO2 nanoparticles/Ti3C2Tx MXene nanoflakes is used as the electron transport layer (ETL) in a planar regular-structure PSC. The results indicate that by changing the Ti3C2Tx/SnO2 ratios (0-2.2 wt %) in ETLs, the film qualities of top perovskite layers are controllable, including the compactness, crystal size, surface roughness, crystallinity, optical absorption, defect density, and so forth. The defect density in perovskite films is substantially reduced from 5.65 × 1015 to 2.25 × 1015 cm-3 using an optimized hybrid ETL (1.4 wt %) compared with the pristine SnO2, while the electrical conductivity of the hybrid ETL is decreased probably due to the geometric factor of the incorporated MXene. As a result, the power conversion efficiency of PSCs is significantly increased from 16.28 to 20.35%, and the environmental stability of the unencapsulated devices is greatly improved. This work provides a facile, robust, and effective way to reduce defects in perovskite films by using emerging MXene nanomaterials and might also be useful to other perovskite-based (opto)electronic devices such as light-emitting diodes and photodetectors.