Dew point temperature as an invariant replacement for relative humidity for advanced perovskite solar cell fabrication systems

The ambient environment plays a pivotal role in the formation of organic-inorganic halide perovskite films. In particular, a certain level of humidity during the fabrication process can promote the crystallization of perovskites, resulting in better film morphologies and enhanced photovoltaic performances. Here, we unravel the importance of thermal equilibrium on the effect of relative humidity during perovskite film fabrication. We show that crystal quality is highly influenced by the dew point even when the relative humidity is unchanged. Observations related to the importance of the dew point on the material morphology, crystal quality, and resultant photovoltaic properties shed light on the dew point as a universal parameter affecting perovskite film fabrication.