Efficient surface passivation of perovskite films by a post-treatment method with a minimal dose

Post-treatment of a perovskite film is known to be an efficient way to passivate surface defects in perovskite solar cells (PSCs). Conventionally, post-treatment with organic iodides has been performed on the annealed perovskite phase (abbreviated as APP-PT) which, however, forms undesirable excess iodides on the surface that can generate interstitial iodine defects causing poor stability. Here, we report an efficient post-treatment process that is performed on the as-deposited un-annealed intermediate phase (abbreviated as UIP-PT). This method enables an effective passivation of the perovskite film surface with a minimal organic iodide passivation agent (100-fold reduced concentration compared with the conventional method) to prevent the surplus iodides. The trap density (n(t)) of the perovskite film is substantially decreased from 1.62 x 10(16) cm(-3) (untreated sample) to 1.24 x 10(16) cm(-3) after UIP-PT, while little change in n(t) is observed for the conventional method (n(t) = 1.41 x 10(16) cm(-3)). Furthermore, negligible current-voltage hysteresis is observed in the UIP-PT sample because of the increased activation energy for ion migration. As a result of suppressed ion migration and the reduced traps, the device based on the UIP-PT demonstrates improved stability in the dark and under illumination, maintaining 96.37% of the initial PCE after 1750 h of storage.