All-Vacuum Processed Methylammonium-free Perovskite Solar Cells in p-i-n Architecture via a Sequential Layer Deposition Process
Alexander Diercks a b, Thomas Feeney a b, Julian Petry a b, Ahmed Farag a b, Roja Singh a b, Ulrich Paetzold a b, Paul Fassl a b
a Light Technology Institute, Karlsruhe Institute of Technology, Engesserstrasse 13, 76131 Karlsruhe, Germany
b Institute of Microstructure Technology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)
#PerFut - Metal Halide Perovskites Fundamental Approaches and Technological Challenges
VALÈNCIA, Spain, 2023 March 6th - 10th
Organizers: Wang Feng, Giulia Grancini and Pablo P. Boix
Poster, Alexander Diercks, 356
Publication date: 22nd December 2022

Perovskite solar cells (PSCs) are a promising candidate for next-generation photovoltaics and showed an incredible increase in performance during the last decade reaching record power conversion efficiencies (PCEs) > 25%. Vacuum deposition techniques are widely used for fabrication of thin-films and have several advantages compared to solution-based fabrication methods. These include conformal deposition of high-quality layers, low material consumption and the ease of scalability to larger areas. However, PCEs of thermally evaporated PSCs have been lacking behind those of solution-processed PSCs for years. While originally most research regarding thermally evaporated PSCs was dedicated to co-evaporation processes reaching maximum PCEs of 20.6% [1], recent record PCEs > 21% were achieved via sequential layer deposition approaches in the n-i-p architecture.[2,3] Here, the individual materials for the perovskite layer are deposited in multiple steps and converted to perovskite during a subsequent annealing step.

In this work, we show the first ever p-i-n all-vacuum processed methylammonium-free PSCs via a sequential layer deposition approach. In the first deposition step, lead iodide (PbI2) and caesium iodide (CsI) are co-evaporated onto the substrate. The amount of formamidinium (FA) iodide needs to be optimized by tuning its layer thickness in a second evaporation step. During an optimized annealing step under ambient atmosphere, the two layers are converted into a perovskite film with a final composition of Cs0.15FA0.85PbI3 and a bandgap of 1.54 eV. Comparing different vacuum-processed hole transport layers (HTLs) we find a similar microstructure and crystallinity with X-ray diffraction measurements and observe a conformal and homogeneous coverage via scanning electron microscope imaging. Additionally, we studied the optoelectronic properties of the fabricated films and reached high photoluminescence quantum yields above 1%. Using our recently developed evaporated MeO-2PacZ self-assembled monolayer as HTL we achieve PCEs beyond 17%.[4]

With our work, we pave the way for efficient all-evaporated PSCs and their application to monolithic tandem solar cells with an up-scalable and industrially relevant deposition technique. The next goals are to further push the efficiency and change the perovskite composition to obtain bandgaps relevant for tandem solar cells.

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