Simultaneously enhanced moisture tolerance and defect passivation of perovskite solar cells with cross-linked grain encapsulation

Abstract The grain surfaces (film surface and grain boundary) of polycrystalline perovskite films are vulnerable sites in solar cells since they pose a high defect density and initiate the degradation of perovskite absorber. Achieving simultaneously defect passivation and grain protection from moisture is crucial for the viability of perovskite solar cells. Here, an in situ cross-linked grain encapsulation (CLGE) strategy that improves both device stability and defect passivation is reported. Cross-linkable semiconducting small molecules are mixed into the antisolvent to uniformly form a compact and conducting cross-linked layer over the grain surfaces. This cross-linked coating layer not only passivates trap states and facilitates hole extraction, but also enhances the device stability by preventing moisture diffusion. Using the CLGE strategy, a high power conversion efficiency (PCE) of 22.7% is obtained in 1.55-eV bandgap planar perovskite solar cells. The unencapsulated devices with CLGE exhibit significantly enhanced device stability again moisture and maintain >90% of their initial PCE after shelf storage under ambient condition for over 10,000 h.