Understanding the formation and transformation of low dimensional capping layers in lead halide perovskites by thermal evaporation
Carlo Andrea Riccardo Perini a, Andres Felipe Castro Mendez a, Jacob Vagott a, Magdalena Ravello a, Juan-Pablo Correa-Baena a
a School of Materials Science and Engineering, Georgia Institute of Technology, North Avenue, Atlanta, United States
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Oral, Carlo Andrea Riccardo Perini, presentation 048
DOI: https://doi.org/10.29363/nanoge.hopv.2022.048
Publication date: 20th April 2022

 In this contribution we compare interfaces treated with PEAI, a bulky cation, via solution and via thermal evaporation. We highlight differences in crystallinity, uniformity, and stability of the layers deposited via the two different routes using measurements as SEM, XPS, GIWAXS, and PL mapping. Finally, we test the bulky cation evaporated layers in complete devices stacks, reaching power conversion efficiencies > 20 %. Our observations highlight that bulky-cations deposited via vapor tend to form really thin layers on the exposed perovskite surface. Once a layer of PEAI is formed, the deposition rate of the organics on the substrate is significantly reduced. Both solution and vapor routes lead to the formation of 2D Ruddlesden-Popper phases at the treated interface, however, the interface termination of the underlying 3D perovskite film proves to play a crucial role in the speed of conversion of the surface to 2D Ruddlesden-Popper structures. The organic layers deposited via vapor lead to highly uniform photoluminescence (PL) from the films, differently from layers deposited from solution that tend to be thicker and less uniform, which is also visible from the SEM images. Benefiting from the decreased thickness and improved uniformities, solar cells incorporating the vapor deposited layers show an increase in the median power conversion efficiency with annealing, which is opposite to the drop observed in the solution treated films. Our observations indicate that vapor deposition routes enable a higher degree of control on the formation of the interface, leading to improved stability for the vapor treated films.

C.A.R.P. thanks Monikandan Rebhadevi for the useful discussion and study material provided for the analysis of the XPS data collected in this work. C.A.R.P. and J.P.C.B. received financial support from the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Solar Energy Technologies Office Award Number DE40 EE0009369. This research used the CMS beamline of National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under contract DE-SC0012704. C.A.R.P. thanks Tim Kodalle, Carolin Sutter-Fella, and the molecular foundry for the help with PL mapping of the perovskite films.

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