Deactivating grain boundary defect by bifunctional polymer additive for humid air-synthesized stable halide perovskite solar cells

At present, the inferior stability compared to the high power conversion efficiency (PCE) for halide perovskite solar cells (PSCs) is the foremost drawback to impede their potential applications. Here, our work incorporate bifunctional polycaprolactone (PCL) agent into perovskite precursors in order to enhance the performance and stability of the humid air-fabricated perovskite solar cells (PSCs). The mechanism of efficiency and stability improvement can be resulted from assist in growth of perovskite grain and passivation of trap states in grain boundaries. The proved reduction of defect-state density can be ascribed to the cross-link function of PCL agent with C O bond, which was distributed along the grain boundaries and could play the synthetic role of Lewis base and acid, consequently resulting in the suppressed carrier recombination both in the bulk perovskite films and interfaces. The corresponding best performance device generates a conversion efficiency of 19.78%, 26.6% higher than that of the pristine device and retains ~88% of the initial values after 21 days’ storage without any encapsulation in ambient air. The proposed bifunctional adding strategy and the mechanism study could probe into the improvement of both efficiency and stability of the PSCs fabricated under fully open air conditions.