Chemical sintering reduced grain boundary defects for stable planar perovskite solar cells

Organic–inorganic hybrid perovskite solar cells have attracted tremendous attention in photovoltaic research, but the presence of massive parasitic traps at the grain boundaries in perovskite films discourages efficient bimolecular recombination and carrier dynamics, which limits device performance and stability. Here we report a simple and fast chemical sintering protocol to substantially reduce grain boundary defects for as-formed films for different PbI₂-templated perovskite materials. With this method parasitic traps on grain boundaries are intrinsically reduced, featuring the Urbach energy reduced by 1.5 meV. For optimal photovoltaic devices, we demonstrate a planar solar cell with power conversion efficiency (PCE) of 19.68% which retains 80% of this efficiency over 720 h in ambient air without any encapsulation. These findings offer a widely applicable, versatile process to efficiently reduce grain boundary defects and will be of interest to many other film material systems afflicted by polydispersity and grain boundary disturbances.