Researchers from Fraunhofer ISE and KAUST built a perovskite-silicon tandem solar cell that reportedly offers improved reproducibility. The device relies on self-assembled monolayers that reportedly result in low parasitic absorption and rapid charge extraction.
An international research team has developed a perovskite-silicon tandem solar cell based on self-assembled monolayers (SAMs) that improve perovskite growth and optoelectronic properties.
“Self-assembled-monolayers (SAMs) are currently used as state-of-the-art hole transport layers in perovskite-based solar cells, offering low parasitic absorption, rapid charge extraction, and effective passivation of the perovskite’s buried interface,” the research’s lead author, Oussama Er-Raji, told pv magazine. “However, controlling their thickness, packing density, and orientation remains highly challenging.”
Specifically, the research team examined the influence of an intrinsic yet previously unexplored process parameter—annealing temperature—on the self-assembly of a conventional SAM, namely 2PACz. “We found that increasing the annealing temperature from the conventional 100 C to 150 C results in a reduction of the SAM thickness from approximately 5 nm to a monolayer of about 1 nm, while simultaneously enhancing its packing density, thereby addressing both major challenges associated with SAMs,” Er-Raji explained.
The investigation was primarily conducted using in situ X-ray photoelectron spectroscopy with scattered electron background analysis, which the scientists said is an effective method for studying ultra-thin layers and holds significant potential for advancing the field. “As a result, the interfacial 2PACz/perovskite passivation quality was enhanced, leading to improvements in the performance of fully-textured perovskite silicon tandem solar cells,” Er-Raji said.
The academics 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.
Tested under standard illumination conditions, the champion device built with the proposed tandem configuration achieved a power conversion efficiency of 29.8%. “With our strategy, a 1.3% power conversion efficiency increment is obtained in fully-textured perovskite/silicon tandem solar cells, with improved reproducibility,” the researchers said.
The new cell concept was introduced in the paper “Tuning Self-Assembly of Hole-Selective Monolayers for Reproducible Perovskite/Silicon Tandem Solar Cells,” which was recently published in small methods. The research team was formed by scientists from Germany’s Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) and the Fraunhofer Center for Silicon Photovoltaics CSP, as well as the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.
“The study improves our understanding of the self-assembly of SAMs, and demonstrates that the efficiency potential of perovskite-based solar cells with SAMs is yet to be fully realized,” Er-Raji concluded.