Surface passivation of perovskite films by potassium bis(fluorosulfonyl) imide for efficient solar cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted much attention because of their high photoelectric conversion efficiency (PCE) and simple preparation process. At present, one of the major factors limiting the further improvement of PSCs' performance is defects in perovskite active layers. Herein, we report an effective surface post-treatment method for perovskite active layers, which uses potassium bis(fluorosulfonyl) imide (KFSI) to passivate multiple defects, improve photovoltaic performance and reduce the hysteresis. It is demonstrated that not only S=O and S-N bonds but also charged K+ and FSIxe213; ions in KFSI contribute to the passivation of multiple defects in perovskite films via Lewis acid-base interaction and/or forming ionic bonds. After the optimized KFSI treatment, the trap density of the perovskite film decreased from 8.41 x 1015cmxe213; 3 to 3.97 x 1015cmxe213; 3, which significantly suppressed trap-assisted nonradiative recombination of carriers in perovskite films and/or at perovskite/hole transport layer interface. The KFSI treated device achieved a PCE of ~19.00% with less hysteresis, appreciably outperforming the control device (17.22%). At the same time, the performance reproducibility among the fabricated solar cells was remarkably improved. This work provides a facile way to passivate multiple defects in perovskite films and further enhance the performance of perovskite solar cells.