Low-Temperature Soft-Cover Deposition of Uniform Large-Scale Perovskite Films for High-Performance Solar Cells

Large-scale high-quality perovskite thin films are crucial to produce high-performance perovskite solar cells. However, for perovskite films fabricated by solvent-rich processes, film uniformity can be prevented by convection during thermal evaporation of the solvent. Here, a scalable low-temperature soft-cover deposition (LT-SCD) method is presented, where the thermal convection-induced defects in perovskite films are eliminated through a strategy of surface tension relaxation. Compact, homogeneous, and convection-induced-defects-free perovskite films are obtained on an area of 12 cm², which enables a power conversion efficiency (PCE) of 15.5% on a solar cell with an area of 5 cm². This is the highest efficiency at this large cell area. A PCE of 15.3% is also obtained on a flexible perovskite solar cell deposited on the polyethylene terephthalate substrate owing to the advantage of presented low-temperature processing. Hence, the present LT-SCD technology provides a new non-spin-coating route to the deposition of large-area uniform perovskite films for both rigid and flexible perovskite devices.

For solvent-rich scalable processes, solvents in liquid films are thermally evaporated to form solid films. Due to the temperature difference during heating, the surface tension difference in perovskite precursor is established and drives the convection to form film defects in cellular patterns. The cellular defects can be eliminated via soft-cover deposition through a strategy of surface tension relaxation.

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