An enhanced couette flow printing strategy to recover efficiency losses by area and substrate differences in perovskite solar cells

The uneven crystallization rate of perovskite films causes the inevitable efficiency losses, due to the intrinsic agglomeration of colloidal particles and substrate differences. Herein, a patterned-meniscus coating strategy is introduced to enhance the Couette flow during the printing of perovskite solar cells (PSCs), which avoids the agglomeration in the film entirety. Owing to the introduction of shear strain and extensional flow by the patterned-meniscus coating, generation of the colloidal particle fluxion in the perovskite wet-film state can be greatly decreased, which further inhibits the influence of secondary agglomeration on perovskite films. In addition, patterned-meniscus coating can enhance the printing window tolerance of perovskite films. Consequently, the corresponding inverted PSCs achieve a PCE of 20.08% based on a flexible substrate. More importantly, the sensitivity of colloidal particles to scale and substrate discrepancies can be well reduced. The efficiency loss caused by different areas and substrate conversion decreases from 34.7% to 12.6% (enlarging the scale from 0.04 cm(2) to 1.01 cm(2)), and from 48.2% to 29.3% with the substrate transition (rigid to flexible), respectively. This handleability strategy provides a reference for fabricating high-quality perovskite films and outstanding-performance PSCs.