Sublimated Cyanoacetamide-Driven Surface Recrystallization for Spray-Coated Wide-Bandgap Perovskite Solar Cells

Spray-coated wide-bandgap perovskite solar cells offer a low-cost, highly scalable, and substrate-adaptive fabrication approach, holding significant promise for applications in perovskite-based tandem solar cells. However, the uncontrollable volatilization process and the randomly distributed nucleation sites lead to increasingly severe surface roughness and defect formation in the perovskite films as the number of spray-coated layers increases. Here, a solid-phase cyanoacetamide compound, N,N-dimethyl-2-cyanoacetamide (DMCA), is employed to induce lattice reorganization on the surface of spray-coated perovskite films. DMCA molecules bearing bifunctional groups enter and intercalate into the perovskite lattice by coordinating their carbonyl groups with Pb²⁺ and forming hydrogen bonds between their cyano groups and formamidinium (FA⁺), thereby generating a liquid intermediate state. Upon subsequent heating, DMCA molecules exsolve from the perovskite lattice resulting in lattice reconstruction. Consequently, both surface roughness and defect density are substantially reduced. The optimized wide-bandgap (1.67 eV) solar cells fabricated via spray-coating method deliver a high open-circuit voltage of 1.23 V and achieve a record power conversion efficiency (PCE) of 22.56%. Unencapsulated devices exhibit operational stability, maintaining nearly constant efficiency over 1200 h of maximum power point (MPP) tracking under continuous illumination.