Paper published in ACS Appl. Energy Mater.

Slot-die coating has emerged as a promising deposition method for the industrial-scale production of perovskite solar cells (PSCs); it is compatible with roll-to-roll processing, has high material utilization, and gives precise control over coating parameters. One key challenge is that lead halide perovskites are highly sensitive to moisture. At the laboratory scale, strict environmental controls (i.e., N₂-filled gloveboxes) can be used to mitigate these effects; however, this becomes increasingly challenging and costly as production is scaled up. This study therefore seeks to establish how relative humidity (RH) affects the performance of PSCs fabricated via slot-die coating, i.e., how dry is dry enough for the coating step? Our results show that PSCs fabricated in RHs above 30% show a pronounced decrease in power conversion efficiency (PCE), mainly due to a degradation in film quality; however, at or below 30% RH, the PCE is much less affected. Identifying this processing window is a critically important step in the scale-up of PSC technology that will help inform the level of environmental controls required during manufacture.