Regulate defects and energy levels for perovskite solar cells by co-modification strategy

The under-coordinated bonds and deep-level defects on the perovskite surface always act as non-radiative recombination centers and lead to energy loss. The usual surface modification efficiency is limited because of the diversity of surface terminals and defects. Here, a co-modification strategy is proposed for more-thorough modification by reconstructing and post-modifying perovskite surface defects. In detail, the tetrahydrofuran (THF) is firstly implemented to remove the organic component and expose the perovskite surface with uniform Pb terminals and defects, and then the 4-Methylbenzyl Mercaptan (MBM) is used to form strong R-S-Pb bonding with them, which achieves the increase and decrease of under-coordinated Pb donor defects. Correspondingly, the surface energy level of perovskite is observed a consistent change with defects. THF/MBM co-modification changes the perovskite surface energy level from n-type toward p-type, which enhances the holes' transport efficiency. As a result, the best power conversion efficiency (PCE) increases from 22.23% of the control device to 24.17% of the device with THF/MBM co-modification. Notably, a full-coverage and strong-bonding protective layer is formed by THF/MBM co-modification, which facilitates excellent device stability (Retains 93.7%, after 3360 h in N2). This strategy shows great potential in high-performance PSCs by reconstructing defects and energy level of perovskite surface.