Efficient Carrier Interconnection by the Concept of Thermionic Emission for Monolithic Tandem Solar Cells with Solution-processed Perovskites

In this work, a new thermionic emission-based interconnecting layer (ICL) for all-perovskite tandem cell is demonstrated. Fundamentally, we confirm that the thermionic emission plays a critical role in the electron transport process in the ICL both experimentally and theoretically. Besides achieving high optical transmission and electrical properties, the new ICL chemically protects the underlying perovskite film by introducing a fluoride silane incorporated polyethylenimine ethoxylated (FSIP) hybrid system which also passivates the surface defects to reduce electrical loss. Our monolithic all-perovskite tandem cells demonstrate highest PCE of 17.9% (from current density-voltage scan) and the highest steady-state efficiency is 16.1% for a typical device.