Proceedings of nanoGe Fall Meeting 2021 (NFM21)
DOI: https://doi.org/10.29363/nanoge.nfm.2021.091
Publication date: 23rd September 2021
The functionality of electronic devices to a large extent is governed by the interfaces of semiconductors with contact materials. In solar cells, thermodynamic equilibration of the electrochemical potential of electrons in the absorber and in the contact phases leads to built in electric fields, which under solar excitation give rise to the photo-potential. In this talk it is demonstrated, how photoelectron spectroscopy can be applied to visualize potential variations in space charge regions of thin film solar cells and how these change under illumination.
As photoelectron spectroscopy is a surface analytical method the band structure of buried interfaces classically is determined by step by step experiments using vacuum integrated deposition and PES systems. In order to analyze the electronic structure of ex-situ solution processed devices, we developed tapered cross section photoelectron spectroscopy (TCS-PES) [1]. Here we use a shallow angle wedge to project the nm scale of the normal cross section to the mm scale on the TCS. Line scan PES with local resolution in the 10µm range now gives access to band bending in space charge regions in the dark and operating under illumination. In addition we use in vacuo prepared interfaces and ex situ prepared device stacks of classical and inverted solar cell structures to corroborate the TCS-PES findings [2]. Perovskite absorbers of different compositions are demonstrated to be doped n-type. Simulations of the potential distribution on TCS shows the importance of strong p-doping of the hole extraction layer to obtain large photopotentials.
In contrast to the current believe, we demonstrate that the photoactive interface of efficient MAPI3 and (FAPbI3)0.85(MAPbBr3)0.15 solar cells is a n-p heterojunction i.e. the working principle is n-n-p and not n-i-p.
Many thanks go to my coworkers
Tim Hellmann1, Michael Wussler1, Chittaranjan Das2, Clément Maheu1, and Wolfram Jaegermann1
1 Technische Universität Darmstadt, Department of Materials Science - Surface Science Lab
2 Karlsruhe Institute of Technology (KIT), Institute for Applied Materials - Energy Storage Systems, Germany
and to the cooperation partners
Tobias Abzieher3, Ulrich Paetzold3, Clemens Baretzky4, and Uli Würfel4
3 Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology, Germany
4 Universität Freiburg and Fraunhofer Institut für Solare Energiesysteme.
Funding by DFG Projects "Interrogate" within SPP 2196 and "Inverted solar cells" and
BMBF Project "Perosol" is gratefully acknowledged
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