Improving Performance by Na Doping of a Buffer Layer – Chemical and Electronic Structure of the InxSy:Na /CuIn(S,Se)2 Thin-Film Solar Cell Interface

Authors

Dirk Hauschild, Karlsruhe Institute of Technology (KIT)
Frank Meyer, University of Würzburg
Andreas Benkert, University of Würzburg
Dagmar Kreikemeyer-Lorenzo, Karlsruhe Institute of Technology (KIT)
Thomas Dalibor, AVANCIS GmbH
Jörg Palm, AVANCIS GmbH
Monika A. Blum, University of Nevada, Las Vegas
Wanli Yang, Lawrence Berkeley National LaboratoryFollow
Regan G. Wilks, Helmholtz‐Zentrum Berlin für Materialien und Energie GmbHFollow
Marcus Bär, Helmholtz‐Zentrum Berlin für Materialien und Energie GmbH
Friedrich Reinert, University of Würzburg
Clemens Heske, University of Nevada, Las VegasFollow
Lothar Weinhardt, University of Nevada, Las VegasFollow

Document Type

Article

Publication Date

2-9-2018

Publication Title

Progress in Photovoltaics: Research and Applications

Volume

26

Issue

5

First page number:

359

Last page number:

366

Abstract

Doping an indium sulfide buffer layer with sodium is a promising route to replace the “state‐of‐the‐art” CdS buffer layer in chalcopyrite‐based thin‐film solar cells, as it achieves efficiencies as high as 17.9% for large‐area devices (30 cm × 30 cm). We report on the chemical and electronic structure of the InxSy:Na/CuIn(S,Se)2 (CISSe) interface for thin‐film solar cells by means of photoelectron, soft x‐ray emission, and inverse photoemission spectroscopy. For as‐deposited InxSy:Na buffer layers, we find a sulfur‐poor surface and, in comparison to undoped InxSy and the standard CdS buffer, derive a large electronic surface band gap of 2.60 ± 0.11 eV. The conduction band offset at the buffer/absorber interface is a spike of 0.32 ± 0.10 eV. After annealing at 200°C to simulate the thermal load of subsequent cell manufacturing processes, an additional diffusion of copper and selenium from the absorber towards the buffer layer surface is observed, leading to a distinct electronic surface band gap decrease of the InxSy:Na buffer layer (to 2.11 ± 0.11 eV). We speculate that the diffusion of absorber elements causes a band gap widening at the former absorber surface and that both effects lead to a reduction of the conduction band spike for the buried InxSy:Na/CISSe interface after annealing.

Keywords

Band alignment, Electronic structure, Photoelectron spectroscopy, Thin‐film solar cells, X‐ray emission spectroscopy

Language

eng

Repository Citation

Hauschild, D., Meyer, F., Benkert, A., Kreikemeyer-Lorenzo, D., Dalibor, T., Palm, J., Blum, M. A., Yang, W., Wilks, R. G., Bär, M., Reinert, F., Heske, C., Weinhardt, L. (2018). Improving Performance by Na Doping of a Buffer Layer – Chemical and Electronic Structure of the InxSy:Na /CuIn(S,Se)2 Thin-Film Solar Cell Interface. Progress in Photovoltaics: Research and Applications, 26(5), 359-366.
http://dx.doi.org/10.1002/pip.2993