Inhibition of halide oxidation and deprotonation of organic cations with dimethylammonium formate for air-processed p–i–n perovskite solar cells

The manufacturing of perovskite solar cells under ambient conditions is desirable, yet the efficiency of p–i–n perovskite solar cells fabricated in air still lags behind those made in an inert atmosphere. Here we introduce an ionic pair stabilizer, dimethylammonium formate (DMAFo), into the perovskite precursor solution to prevent the degradation of perovskite precursors. DMAFo inhibits the oxidization of iodide ions and deprotonation of organic cations, improving the crystallinity and reducing defects in the resulting perovskite films. We show the generation of additional p-type defects during ambient air fabrication that suggests the need for improving bulk properties of the perovskite film beyond surface passivation. Upon addition of DMAFo, we demonstrate that the efficiency of inverted p–i–n solar cells based on perovskite layers with 1.53-eV and 1.65-eV bandgaps fabricated under ambient conditions (25–30 °C, 35–50% relative humidity) increases by 15–20%. We achieve a certified stabilized efficiency of 24.72% for the 1.53-eV cell, on a par with state-of-the-art counterparts fabricated in an inert atmosphere.