Band alignment towards high-efficiency NiOx-based Sn-Pb mixed perovskite solar cells

Narrow-bandgap tin-lead (Sn-Pb) mixed perovskite solar cells (PSCs) play a key role in constructing perovskite tandem solar cells that are potential to overpass Shockley-Queisser limit. A robust, chemically stable and lowtemperature-processed hole transporting layer (HTL) is essential for building high-efficiency Sn-Pb solar cells and perovskite tandem solar cells. Here, we explore a roomtemperature-processed NiOx (L-NiOx) HTL based on nanocrystals (NCs) for Sn-Pb PSCs. In comparison with hightemperature-annealed NiOx (H-NiOx) film, the L-NiOx film shows deeper valence band and lower trap density, which increases the built-in potential and reduces carrier recombination, leading to a power conversion efficiency of 18.77%, the record for NiOx-based narrow-bandgap PSCs. Furthermore, the device maintains about 96% of its original efficiency after 50 days. This work provides a robust and room-temperatureprocessed HTL for highly efficient and stable narrow-bandgap PSCs.