@misc{BaerSchubertMarsenetal., author = {B{\"a}r, Marcus and Schubert, Bj{\"o}rn-Arvid and Marsen, Bj{\"o}rn and Wilks, Regan G. and Pookpanratana, Sujitra and Blum, Monika and Krause, Stefan and Unold, Thomas and Yang, Wan Li and Weinhardt, Lothar and Heske, Clemens and Schock, Hans-Werner}, title = {Cliff-like conduction band offset and KCN-induced recombination barrier enhancement at the CdS/Cu2ZnSnS4 thin-film solar cell heterojunction}, abstract = {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.}, language = {en} } @misc{SullivanWilksWinkleretal., author = {Sullivan, J. T. and Wilks, Regan G. and Winkler, M. T. and Weinhardt, Lothar and Recht, D. and Said, A. J. and Newman, B. K. and Zhang, Y. and Blum, Monika and Krause, S. and Yang, Wan Li and Heske, Clemens and Aziz, M. J. and B{\"a}r, Marcus and Buonassisi, T.}, title = {Soft x-ray emission spectroscopy studies of the electronic structure of silicon supersaturated with sulfur}, abstract = {We apply soft x-ray emission spectroscopy (XES) to measure the electronic structure of crystalline silicon supersaturated with sulfur (up to 0.7 at. \%), a candidate intermediate-band solar cell material. Si L2,3 emission features are observed above the conventional Si valence band maximum, with intensity scaling linearly with S concentration. The lineshape of the S-induced features change across the insulator-to-metal transition, indicating a significant modification of the local electronic structure concurrent with the change in macroscopic electronic behavior. The relationship between the Si L2,3 XES spectral features and the anomalously high sub-band gap infrared absorption is discussed.}, language = {en} } @misc{BaerSchubertMarsenetal., author = {B{\"a}r, Marcus and Schubert, Bj{\"o}rn-Arvid and Marsen, Bj{\"o}rn and Wilks, Regan G. and Blum, M. and Krause, S. and Pookpanratana, Sujitra and Zhang, Y. and Unold, Thomas and Yang, W. and Weinhardt, Lothar and Heske, Clemens and Schock, Hans-Werner}, title = {Cu2ZnSnS4 thin-film solar cell absorbers illuminated by soft x-rays}, series = {Journal of Materials Research}, volume = {27}, journal = {Journal of Materials Research}, number = {8}, issn = {2044-5326}, doi = {10.1557/jmr.2012.59}, pages = {1097 -- 1104}, abstract = {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.}, language = {en} } @misc{WeinhardtBenkertMeyeretal., author = {Weinhardt, Lothar and Benkert, Andreas and Meyer, Frank and Blum, Monika and Wilks, Regan G. and Yang, Wan Li and B{\"a}r, Marcus and Reinert, Friedrich and Heske, Clemens}, title = {Nuclear dynamics and spectator effects in resonant inelastic soft x-ray scattering of gas-phase water molecules}, series = {The journal of chemical physics}, volume = {136}, journal = {The journal of chemical physics}, number = {14}, issn = {1089-7690}, pages = {144311}, abstract = {The electronic structure of gas-phase H2O and D2O molecules has been investigated using resonant inelastic soft x-ray scattering (RIXS). We observe spectator shifts for all valence orbitals when exciting into the lowest three absorption resonances. Strong changes of the relative valence orbital emission intensities are found when exciting into the different absorption resonances, which can be related to the angular anisotropy of the RIXS process. Furthermore, excitation into the 4a1 resonance leads to nuclear dynamics on the time scale of the RIXS process; we find evidence for vibrational coupling and molecular dissociation in both, the spectator and the participant emission.}, language = {en} } @misc{MeyerWeinhardtBlumetal., author = {Meyer, Frank and Weinhardt, Lothar and Blum, Mia and B{\"a}r, Marcus and Wilks, Regan G. and Yang, Wooyong and Heske, Clemens and Reinert, F.}, title = {Non-equivalent carbon atoms in the resonant inelastic soft X-ray scattering map of cysteine}, series = {The journal of chemical physics}, volume = {138}, journal = {The journal of chemical physics}, number = {3}, issn = {1089-7690}, pages = {034306}, abstract = {Resonant inelastic soft x-ray scattering (RIXS) was used to study the electronic structure of solid cysteine films. A RIXS map approach, i.e., plotting the x-ray emission intensity as a function of excitation and emission energy, allows us to separate the contributions of the three chemically nonequivalent carbon atoms in cysteine. In particular, we can identify orbitals localized near the photoexcited atoms, as well as orbitals that are delocalized over the entire molecule.}, language = {en} } @misc{BaerKlaerDuarteetal., author = {B{\"a}r, Marcus and Klaer, Joachim and Duarte, Roberto Felix and Barreau, Nicolas and Weinhardt, Lothar and Wilks, Regan G. and Heske, Clemens and Schock, Hans-Werner}, title = {Surface Off-Stoichiometry of CuInS2 Thin-Film Solar Cell Absorbers}, series = {IEEE Journal of Photovoltaics}, volume = {3}, journal = {IEEE Journal of Photovoltaics}, number = {2}, issn = {2156-3381}, pages = {828 -- 832}, abstract = {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.}, language = {en} } @misc{BaerKlaerWeinhardtetal., author = {B{\"a}r, Marcus and Klaer, Joachim and Weinhardt, Lothar and Wilks, Regan G. and Krause, Stefan and Blum, Monika and Yang, Wan Li and Heske, Clemens and Schock, Hans-Werner}, title = {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}, series = {Advanced Energy Materials}, volume = {3}, journal = {Advanced Energy Materials}, number = {6}, issn = {1614-6840}, pages = {777 -- 781}, abstract = {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.}, language = {en} } @inproceedings{BaerStarrLambertzetal., author = {B{\"a}r, Marcus and Starr, David E. and Lambertz, Andreas and Holl{\"a}nder, B. and Alsmeier, Jan Hendrik and Weinhardt, Lothar and Blum, Mia and Gorgoi, Mihaela and Yang, Wooyong and Wilks, Regan G. and Heske, Clemens}, title = {Microcrystalline silicon oxides for silicon-based solar cells: Impact of the O/Si ratio on the electronic structure}, series = {Thin films for solar and energy technology VI : 17, 18 and 20 August 2014, San Diego, California, United States}, booktitle = {Thin films for solar and energy technology VI : 17, 18 and 20 August 2014, San Diego, California, United States}, editor = {Eldada, Louay A. and Heben, Michael J.}, publisher = {SPIE}, address = {Bellingham, Wash.}, isbn = {978-1-62841-204-8}, doi = {10.1117/12.2061902}, language = {en} } @misc{BaerCouzinieDevyDuarteetal., author = {B{\"a}r, Marcus and Couzini{\`e}-Devy, Fran{\c{c}}ois and Duarte, Roberto Felix and Klaer, Joachim and Pookpanratana, Sujitra and Blum, Monika and Zhang, Yi and Denlinger, Jonathan D. and Yang, Wanli and Wilks, Regan G. and Weinhardt, Lothar and Schock, Hans-Werner and Southerland Kessler, Jude and Heske, Clemens}, title = {The Heavily Intermixed In2S3/Cu(In,Ga)Se2 Interface as Revealed by Photoelectron and Soft X-ray Emission Spectroscopy}, series = {2013 IEEE 39th Photovoltaic Specialists Conference, (PVSC 2013), Tampa, Florida, USA, 16 - 21 June 2013}, journal = {2013 IEEE 39th Photovoltaic Specialists Conference, (PVSC 2013), Tampa, Florida, USA, 16 - 21 June 2013}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4799-3300-6}, doi = {10.1109/PVSC.2013.6744280}, pages = {857 -- 862}, language = {en} } @misc{BenkertMeyerHauschildetal., author = {Benkert, Andreas and Meyer, Frank and Hauschild, Dirk and Blum, Monika and Yang, Wooyong and Wilks, Regan G. and B{\"a}r, Marcus and Reinert, Friedrich and Heske, Clemens and Weinhardt, Lothar}, title = {Isotope Effects in the Resonant Inelastic Soft X-ray Scattering Maps of Gas-Phase Methanol}, series = {The Journal of Physical Chemistry: A}, volume = {120}, journal = {The Journal of Physical Chemistry: A}, number = {14}, issn = {1089-5639}, doi = {10.1021/acs.jpca.6b02636}, pages = {2260 -- 2267}, language = {en} } @misc{BaerBarreauCouzinieDevyetal., author = {B{\"a}r, Marcus and Barreau, Nicolas and Couzini{\´e}-Devy, Fran{\c{c}}ois and Weinhardt, Lothar and Wilks, Regan G. and Kessler, John and Heske, Clemens}, title = {Impact of annealing-induced intermixing on the electronic level alignment at the In₂S₃/Cu(In,Ga)Se₂ thin-film solar cell interface}, series = {ACS Applied Materials \& Interfaces}, volume = {8}, journal = {ACS Applied Materials \& Interfaces}, number = {3}, issn = {1944-8244}, doi = {10.1021/acsami.5b10614}, pages = {2120 -- 2124}, language = {en} } @misc{DuncanKephartHorsleyetal., author = {Duncan, Douglas A. and Kephart, Jason M. and Horsley, Kimberly and Blum, Monika and Mezher, Michelle and Weinhardt, Lothar and H{\"a}ming, Marc and Wilks, Regan G. and Hofmann, Timo and Yang, Wanli and B{\"a}r, Marcus and Sampath, Walajabad S. and Heske, Clemens}, title = {Characterization of sulfur bonding in CdS:O buffer layers for CdTe-based thin-film solar cells}, series = {ACS Applied Materials \& Interfaces}, volume = {7}, journal = {ACS Applied Materials \& Interfaces}, number = {30}, issn = {1944-8244}, doi = {10.1021/acsami.5b03503}, pages = {16382 -- 16386}, language = {en} } @misc{HauschildMeyerBenkertetal., author = {Hauschild, Dirk and Meyer, Frank and Benkert, Andreas and Kreikemeyer-Lorenzo, Dagmar and Pohlner, Stephan and Palm, J{\"o}rg and Blum, Monika and Yang, Wanli and Wilks, Regan G. and B{\"a}r, Marcus and Heske, Clemens and Weinhardt, Lothar and Reinert, Friedrich}, title = {Annealing-induced effects on the chemical structure of the In₂S₃/CuIn(S,Se)₂ thin-film solar cell interface}, series = {The Journal of Physical Chemistry: C, Nanomaterials and interfaces}, volume = {119}, journal = {The Journal of Physical Chemistry: C, Nanomaterials and interfaces}, number = {19}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b01622}, pages = {10412 -- 10416}, language = {en} }