Ink Design Enabling Slot-Die Coated Perovskite Solar Cells with >22% Power Conversion Efficiency, Micro-Modules, and 1 Year of Outdoor Performance Evaluation

The next technological step in the exploration of metal-halide perovskite solar cells is the demonstration of larger-area device prototypes under outdoor operating conditions. The authors here demonstrate that when slot-die coating the halide perovskite layers on large areas, ribbing effects may occur but can be prevented by adjusting the precursor ink's rheological properties. For formamidinium lead triiodide (FAPbI₃) precursor inks based on 2-methoxyethanol, the ink viscosity is adjusted by adding acetonitrile (ACN) as a co-solvent leading to smooth FAPbI₃ thin-films with high quality and layer homogeneity. For an optimized content of 46 vol% of the ACN co-solvent, a certified steady-state performance of 22.3% is achieved in p-i-n FAPbI₃-perovskite solar cells. Scaling devices to larger areas by making laser series-interconnected mini-modules of 12.7 cm², a power conversion efficiency of 17.1% is demonstrated. A full year of outdoor stability testing with continuous maximum power point tracking on encapsulated devices is performed and it is demonstrated that these devices maintain close to 100% of their initial performance during winter and spring followed by a significant performance decline during warmer summer months. This work highlights the importance of the real-condition evaluation of larger area device prototypes to validate the technological potential of halide perovskite photovoltaics.