Researchers from Fraunhofer ISE and King Abdullah University of Science and Technology (KAUST) have designed a perovskite-silicon tandem solar cell that is said to offer improved reproducibility. The device uses self-assembled monolayers (SAMs) that reportedly result in low parasitic absorption and rapid charge extraction.
Schematic of the fully-textured perovskite/silicon tandem solar cell structure studied. Image from: small methods
SAMs have shown great potential as hole-selective contacts for high-efficiency PSCs due to their easy processing, passivation capability, and low parasitic absorption. However, for the deposition of SAMs with a monolayer thickness and a high packing density on metal oxide substrates, critical challenges persist. To address these, the study focuses on the impact of annealing temperature – an intrinsic yet so far unexplored process parameter – during the formation of SAMs.
By performing in situ angle-resolved X-ray photoelectron spectroscopy combined with advanced data analysis routines, it was revealed that increasing the annealing temperature reduces the formed SAM layer thickness from a multilayer stack of ≈5 nm at 100 °C (conventional temperature employed in literature) to a monolayer at 150 °C.
Furthermore, denser adsorption of the SAM to the metal oxide surface is promoted at high temperatures, which enhances the interfacial SAM/perovskite passivation quality.
The scientists built the tandem cell with a top inverted perovskite device based on an indium tin oxide (ITO) substrate, the 2PACz layer, a perovskite absorber, an electron transport layer (ETL) made of buckminsterfullerene (C60), a tin oxide (SnOx) buffer layer, an ITO buffer layer, a silver (Ag) metal contact, and an anti-reflective coating based on magnesium fluoride (MgF2). The bottom cell was based on a heterojunction (HJT) architecture.
The team stated that "With this strategy, a 1.3% power conversion efficiency (PCE) increment is obtained in fully-textured perovskite/silicon tandem solar cells, with improved reproducibility, and a champion device approaching 30% PCE. This study advances the understanding of SAMs formation and presents a promising strategy for further progress in high-efficiency perovskite-based solar cells".
This proposed strategy could be beneficial for large area devices, and the findings of the study could pave the way for further enhancements in the efficiency of perovskite-based solar cells.
