Internal Interactions between Mixed Bulky Organic Cations on Passivating Defects in Perovskite Solar Cells

In perovskite solar cells (PSCs), bulky organic cation halide salt additions play a significant role in suppressing nonradiative recombination by passivating intrinsic defects in perovskites. Herein, a passivation treatment is developed by applying mixed bulky cations [guanidinium cation (GA + ) and phenylethylammonium cations (PEA + )] as the additive for perovskite thin films. The internal interactions between the two bulky cations could result in lower carrier trap-state densities, a sharper Urbach tail, and better carrier transport in perovskite films in comparison with a control film. As a result, in comparison to the control device, which has a power conversion efficiency (PCE) of 18.92%, the mixed-cation-based device exhibits a dramatic enhancement of PCE of 20.64%. Importantly, after 720 h of storage in an ambient atmosphere with a relative humidity (RH) of 60–80% at room temperature, the mixed-cation-based device retains 62.7% of its original performance, whereas the control devices decay to less than 40% of their original performance.