Green Solution Bathing Process for Efficient Large-area Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) towards practical application relies on high efficiency, long lifetime, low toxicity and device upscaling. To realize large-area PSCs, a green solution bathing strategy is delivered to prepare high-performance PSCs. By utilizing 2-pentanol as a green solvent and formamidinium chloride (FACl) as a solute in the green solution bathing, perovskite films with enlarged grain sizes, improved crystallinity and alleviated defect state density were obtained, resulting in the enhancement in the power conversion efficiency of PSCs. Coupled with 2-pentanol and FACl, a champion efficiency of 21.03% for small cells (0.103 cm2) and over 18% for large size (1.00 cm2) were obtained based on the GSB process, which can outperform its counterpart made from commonly-used anti-solvent dropping method. In addition, a large perovskite film (5 cm  5 cm) with obvious mirror effect was successfully prepared. Our innovative approach paves the way to promote device upscaling of PSCs via environment-friendly technique.