TY - GEN A1 - Bär, Marcus A1 - Schubert, Björn-Arvid A1 - Marsen, Björn A1 - Wilks, Regan G. A1 - Pookpanratana, Sujitra A1 - Blum, Monika A1 - Krause, Stefan A1 - Unold, Thomas A1 - Yang, Wan Li A1 - Weinhardt, Lothar A1 - Heske, Clemens A1 - Schock, Hans-Werner T1 - Cliff-like conduction band offset and KCN-induced recombination barrier enhancement at the CdS/Cu2ZnSnS4 thin-film solar cell heterojunction N2 - The electronic structure of the CdS/Cu2ZnSnS4 (CZTS) heterojunction was investigated by direct and inverse photoemission. The effects of a KCN etch of the CZTS absorber prior to CdS deposition on the band alignment at the respective interface were studied. We find a “cliff”-like conduction band offset at the CdS/CZTS interface independent of absorber pretreatment and a significant etch-induced enhancement of the energetic barrier for charge carrier recombination across the CdS/CZTS interface. KW - kesterite KW - thin-film solar cells KW - energy band alignment Y1 - 2011 ER - TY - GEN A1 - Bär, Marcus A1 - Schubert, Björn-Arvid A1 - Marsen, Björn A1 - Krause, Stefan A1 - Pookpanratana, Sujitra A1 - Unold, Thomas A1 - Weinhardt, Lothar A1 - Heske, Clemens A1 - Schock, Hans-Werner T1 - Impact of KCN etching on the chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers N2 - The chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers has been investigated by direct and inverse photoemission. Particular emphasis was placed on the impact of KCN etching, which significantly alters the surface composition and is best explained by a preferred etching of Cu and, to a lesser degree, Sn. As a consequence the surface band gap increased from (1.53 +/- 0.15) eV, which agrees with optically derived bulk band gap values, to (1.91 +/- 0.15) ev. KW - kesterite KW - thin-film solar cells KW - electronic surface structure Y1 - 2011 ER - TY - GEN A1 - Bär, Marcus A1 - Schubert, Björn-Arvid A1 - Marsen, Björn A1 - Wilks, Regan G. A1 - Blum, M. A1 - Krause, S. A1 - Pookpanratana, Sujitra A1 - Zhang, Y. A1 - Unold, Thomas A1 - Yang, W. A1 - Weinhardt, Lothar A1 - Heske, Clemens A1 - Schock, Hans-Werner T1 - Cu2ZnSnS4 thin-film solar cell absorbers illuminated by soft x-rays T2 - Journal of Materials Research N2 - In view of the complexity of thin-film solar cells, which are comprised of a multitude of layers, interfaces, surfaces, elements, impurities, etc., it is crucial to characterize and understand the chemical and electronic structure of these components. Because of the high complexity of the Cu2ZnSn(S,Se)4 compound semiconductor absorber material alone, this is particularly true for kesterite-based devices. Hence, this paper reviews our recent progress in the characterization of Cu2ZnSnS4 (CZTS) thin films. It is demonstrated that a combination of different soft x-ray spectroscopies is an extraordinarily powerful method for illuminating the chemical and electronic material characteristics from many different perspectives, ultimately resulting in a comprehensive picture of these properties. The focus of the article will be on secondary impurity phases, electronic structure, native oxidation, and the CZTS surface composition. Y1 - 2012 U6 - https://doi.org/10.1557/jmr.2012.59 SN - 2044-5326 VL - 27 IS - 8 SP - 1097 EP - 1104 ER - TY - GEN A1 - Bär, Marcus A1 - Klaer, Joachim A1 - Duarte, Roberto Felix A1 - Barreau, Nicolas A1 - Weinhardt, Lothar A1 - Wilks, Regan G. A1 - Heske, Clemens A1 - Schock, Hans-Werner T1 - Surface Off-Stoichiometry of CuInS2 Thin-Film Solar Cell Absorbers T2 - IEEE Journal of Photovoltaics N2 - In this paper, X-ray photoelectron and X-ray-excited Auger electron spectroscopy was used to investigate the chemical surface structure of CuInS2 thin-film solar cell absorbers.We find that the [In]/[Cu] surface composition can vary between 1.6 (±0.4) and 3.7 (±0.7), depending on relatively minor variations in the absorber formation process and/or whether additional wet-chemical treatments are performed. These variations are primarily due to differences in the Cu surface concentration. The corresponding change of the modified In Auger parameter is interpreted as being indicative of a change in the chemical environment of In as a function of Cu off-stoichiometry. Y1 - 2013 UR - https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6380521 SN - 2156-3381 VL - 3 IS - 2 SP - 828 EP - 832 ER - TY - GEN A1 - Bär, Marcus A1 - Klaer, Joachim A1 - Weinhardt, Lothar A1 - Wilks, Regan G. A1 - Krause, Stefan A1 - Blum, Monika A1 - Yang, Wan Li A1 - Heske, Clemens A1 - Schock, Hans-Werner T1 - Cu 2−x S Surface Phases and Their Impact on the Electronic Structure of CuInS 2 Thin Films – A Hidden Parameter in Solar Cell Optimization T2 - Advanced Energy Materials N2 - The surface properties of CuInS 2 (CIS) thin-fi lm solar cell absorbers are investigated by a combination of electron and soft X-ray spectroscopies. Spatially separated regions of varying colors are observed and identifi ed to be dominated by either CuS or Cu 2 S surface phases. After their removal by KCN etching, the samples cannot be distinguished by eye and the CIS surface is found to be Cu-defi cient in both regions. However, a signifi cantly more pronounced off-stoichiometry in the region initially covered by Cu 2 S can be identifi ed. In this region, the resulting surface band gap is also signifi cantly larger than the E g Surf of the initially CuS-terminated region. Such variations may represent a hidden parameter which, if overlooked, induces irreproducibility and thus prevents systematic optimization efforts. Y1 - 2013 SN - 1614-6840 VL - 3 IS - 6 SP - 777 EP - 781 ER - TY - GEN A1 - Bär, Marcus A1 - Couziniè-Devy, François A1 - Duarte, Roberto Felix A1 - Klaer, Joachim A1 - Pookpanratana, Sujitra A1 - Blum, Monika A1 - Zhang, Yi A1 - Denlinger, Jonathan D. A1 - Yang, Wanli A1 - Wilks, Regan G. A1 - Weinhardt, Lothar A1 - Schock, Hans-Werner A1 - Southerland Kessler, Jude A1 - Heske, Clemens T1 - The Heavily Intermixed In2S3/Cu(In,Ga)Se2 Interface as Revealed by Photoelectron and Soft X-ray Emission Spectroscopy T2 - 2013 IEEE 39th Photovoltaic Specialists Conference, (PVSC 2013), Tampa, Florida, USA, 16 - 21 June 2013 Y1 - 2013 SN - 978-1-4799-3300-6 SN - 978-1-4799-3299-3 U6 - https://doi.org/10.1109/PVSC.2013.6744280 SP - 857 EP - 862 PB - IEEE CY - Piscataway, NJ ER -