Efficient perovskite solar modules with an ultra-long processing window enabled by cooling stabilized intermediate phases

Perovskite solar cells (PSCs) have shown promising progress in efficiency and stability, but their application needs further development from small-area cells to large-area modules. When fabricating solar cell modules on large-area substrates, it takes a longer time to deposit and process the thin film than for small area devices. Therefore, it is required to expand the processing window of the solution process. Here, we showed that combining N-methyl-2-pyrrolidone solvent with a cooling strategy can generate more stable FA-based perovskite intermediates in two-step deposition, realizing a longer annealing window. The power conversion efficiency (PCE) of 25.21% for small-area devices (0.045 cm²) and 23.60% for large-area devices (1.00 cm²) was achieved. It is found that cooling the intermediate phase at a temperature close to 0 °C can suppress the formation of δ-phase FAPbI₃ and expand the annealing window by 20-fold (from 9 min to 180 min). With these cooling strategies, we have successfully fabricated uniform perovskite films in a large area of 45 cm². PSC mini-modules made by this method achieved state-of-the-art efficiencies of 22.34% and a certified efficiency of 21.51%. More importantly, even with an annealing delay time of 180 min, the modules attain a decent PCE of 20.89%, showing an ultra-long processing window for fabricating efficient PSCs. Our strategy of stabilizing the perovskite intermediate phase brings great flexibility to the large-scale production of perovskite solar modules.