Locally Supersaturated Inks for a Slot‐Die Process to Enable Highly Efficient and Robust Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs), which debuted with a lot of attention based on high efficiency, are establishing as one of the most promising thin‐film photovoltaic technologies. Currently, research for upscaling and commercialization through eco‐friendly solvent and process systems is being attempted. This study introduces for the first time a rheological engineering‐based locally supersaturated perovskite ink (LSPI) strategy for slot‐die process‐based PSC fabrication suitable for roll‐to‐roll continuous processes. Here, for the greenable slot‐die process, a perovskite precursor ink composed of a low‐toxic dimethyl sulfoxide (DMSO) single solvent is used and a small amount of 1,2‐dichlorobenzene (DCB) is utilized as a modulator to control the rheological properties of the ink. The addition of DCB lowers the high surface tension of the DMSO‐based perovskite precursor ink to suit the slot‐die process, enabling uniform wet film formation, and produces locally supersaturated colloids, i.e., perovskite seeds, that help growth into dense and large grains by heterogeneous nucleation with low Gibbs‐free energy. As a result, the LSPI enables slot‐die coating‐based PSCs with an efficiency of 20.61% (active areas of 0.1 cm 2 ), which allow high efficiencies of 18.66% and 17.66% (active areas of 2.7 and 8.64 cm 2 ) to be achieved in scale‐up to minimodules, respectively.