A research team led by Prof. YANG Dong from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Dalian Jiaotong University, has developed a synergistic additive strategy for large-area slot-die coating of methylammonium-free (MA-free) perovskite films. This study was recently published in Advanced Materials.

Slot-die coating offers a promising route to industrial-scale perovskite solar cell production, owing to its high material utilization and compatibility with continuous roll-to-roll processing. The MA-free FA_xCs_1-xPbI₃ system enables stable device operation by eliminating volatile methylammonium, but its slower intrinsic crystallization and stronger phase-segregation tendency complicate wet-film control and uniform crystallization during ambient-air coating, and can also compromise film phase stability.

To address these challenges, the team devised a synergistic additive strategy using formamidinium thiocyanate (FASCN) and rubidium thiocyanate (RbSCN). The two additives play complementary roles: FASCN promotes nucleation induced by vacuum-flash treatment and subsequent crystal growth, whereas RbSCN helps stabilize the photoactive perovskite phase. Specifically, Rb⁺ occupies the A site of the perovskite lattice, relaxing lattice strain and lowering the activation energy for formation of the photoactive α-FAPbI₃ phase, thereby suppressing the formation of the non-photoactive δ-FAPbI₃ phase.

Through these complementary effects, the team extended the processing window for uniform perovskite crystallization to more than 100 seconds. The resulting films exhibit a dense microstructure, large grains, a uniform vertical compositional gradient, and reduced residual stress.

The small-area perovskite solar cells delivered a power conversion efficiency (PCE) of 26.16%. A large-area module with an active area of 54.80 cm² reached a PCE of 22.70%, substantially higher than the 15.8% of the control module.

The strategy also improved operational stability. Unencapsulated devices retained 97.76% of their initial efficiency after 1,300 hours of continuous maximum-power-point tracking under AM 1.5G illumination at 65 °C; by comparison, control devices retained only 65.86% under the same conditions.