@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{BaerSchubertMarsenetal., author = {B{\"a}r, Marcus and Schubert, Bj{\"o}rn-Arvid and Marsen, Bj{\"o}rn and Krause, Stefan and Pookpanratana, Sujitra and Unold, Thomas and Weinhardt, Lothar and Heske, Clemens and Schock, Hans-Werner}, title = {Impact of KCN etching on the chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers}, abstract = {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.}, 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{BlumOdeliusWeinhardtetal., author = {Blum, M. and Odelius, Michael and Weinhardt, Lothar and Pookpanratana, Sujitra and B{\"a}r, Marcus and Zhang, Y. and Fuchs, Oliver and Yang, W. and Umbach, Eberhard and Heske, Clemens}, title = {Ultrafast Proton Dynamics in Aqueous Amino Acid Solutions Studied by Resonant Inelastic Soft X‑ray Scattering}, series = {The Journal of physical chemistry : B}, volume = {116}, journal = {The Journal of physical chemistry : B}, number = {46}, issn = {1520-5207}, pages = {13757 -- 13764}, abstract = {Resonant inelastic soft X-ray scattering (RIXS) has been used to study the electronic structure of glycine and lysine in aqueous solution. Upon variation of the pH value of the solution from acidic to basic, major changes of the nitrogen K edge RIXS data are observed for both amino acids, which are associated with the protonation and deprotonation of the amino groups. The experimental results are compared with simulations based on density functional theory, yielding a detailed understanding of the spectral changes, as well as insights into the ultrafast proton dynamics in the intermediate core-excited/ionized state of the RIXS process.}, language = {en} } @misc{HofmannYuFolseetal., author = {Hofmann, Timo and Yu, Ted H. and Folse, Michael and Weinhardt, Lothar and B{\"a}r, Marcus and Zhang, Yufeng and Merinov, Boris V. and Myers, Deborah J. and Goddard, William A. and Heske, Clemens}, title = {Using Photoelectron Spectroscopy and Quantum Mechanics to Determine d‑Band Energies of Metals for Catalytic Applications}, series = {The Journal of Physical Chemistry : C}, volume = {116}, journal = {The Journal of Physical Chemistry : C}, number = {45}, issn = {1932-7455}, pages = {24016 -- 24026}, abstract = {The valence band structures (VBS) of eight transition metals (Fe, Co, Ni, Cu, Pd, Ag, Pt, Au) were investigated by photoelectron spectroscopy (PES) using He I, He II, and monochromatized Al Kα excitation. The influence of final states, photoionization cross-section, and adsorption of residual gas molecules in an ultrahigh vacuum environment are discussed in terms of their impact on the VBS. We find that VBSs recorded with monochromatized Al Kα radiation are most closely comparable to the ground state density of states (DOS) derived from quantum mechanics calculations. We use the Al Kα-excited PES measurements to correct the energy scale of the calculated ground-state DOS to approximate the "true" ground-state d-band structure. Finally, we use this data to test the d-band center model commonly used to predict the electronicproperty/ catalytic-activity relationship of metals. We find that a simple continuous dependence of activity on d-band center position is not supported by our results (both experimentally and computationally).}, 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{HofmannYuFolseetal., author = {Hofmann, Timo and Yu, Ted H. and Folse, Michael and Weinhardt, Lothar and B{\"a}r, Marcus and Zhang, Yufeng and Merinov, Boris V. and Myers, Deborah J. and Goddard, William A. and Heske, Clemens}, title = {Reply to "Comment on 'Using Photoelectron Spectroscopy and Quantum Mechanics to Determine d-Band Energies of Metals for Catalytic Applications'"}, series = {Journal of Physical Chemistry : C}, volume = {117}, journal = {Journal of Physical Chemistry : C}, number = {13}, issn = {1932-7455}, pages = {6916 -- 6917}, 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} } @misc{MezherGarrisMansfieldetal., author = {Mezher, Michelle and Garris, Rebekah and Mansfield, Lorelle M. and Blum, Monika and Hauschild, Dirk and Horsley, Kimberly and Duncan, Douglas A. and Yang, Wooyong and B{\"a}r, Marcus and Weinhardt, Lothar and Ramanathan, Kannan and Heske, Clemens}, title = {Soft x-ray spectroscopy of a complex heterojunction in high-efficiency thin-film photovoltaics: Intermixing and Zn speciation at the Zn(O,S)/Cu(In,Ga)Se2 interface}, series = {ACS Applied Materials \& Interfaces}, volume = {8}, journal = {ACS Applied Materials \& Interfaces}, number = {48}, issn = {1944-8244}, doi = {10.1021/acsami.6b09245}, pages = {33256 -- 33263}, language = {en} } @misc{JeyachandranMeyerBenkertetal., author = {Jeyachandran, Y. L. and Meyer, Frank and Benkert, Andreas and B{\"a}r, Marcus and Blum, Monika and Yang, Wooyong and Reinert, Friedrich and Heske, Clemens and Weinhardt, Lothar and Zharnikov, Michael}, title = {Investigation of the ionic hydration in aqueous salt solutions by soft x‑ray emission spectroscopy}, series = {Journal of Physical Chemistry B: Condensed Matter, Materials, Surfaces, Interfaces \& Biophysical Chemistry}, volume = {120}, journal = {Journal of Physical Chemistry B: Condensed Matter, Materials, Surfaces, Interfaces \& Biophysical Chemistry}, number = {31}, issn = {1520-5207}, doi = {10.1021/acs.jpcb.6b03952}, pages = {7687 -- 7695}, 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{WeinhardtFuchsFischeretal., author = {Weinhardt, Lothar and Fuchs, Oliver and Fischer, Andr{\´e} and Weigand, Markus and Meyer, Frank and Benkert, Andreas and Blum, Monika and B{\"a}r, Marcus and Pookpanratana, Sujitra and Denlinger, Jonathan D. and Heske, Clemens and Umbach, Eberhard}, title = {Site- and Symmetry-resolved Resonant X-ray Emission Study of a Highly-ordered PTCDA Thin Film}, series = {The Journal of Physical Chemistry: C}, volume = {120}, journal = {The Journal of Physical Chemistry: C}, number = {16}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b12422}, pages = {8607 -- 8615}, language = {en} } @misc{MezherGarrisMansfieldetal., author = {Mezher, Michelle and Garris, Rebekah and Mansfield, Lorelle M. and Horsley, Kimberly and Weinhardt, Lothar and Duncan, Douglas A. and Blum, Monika and Rosenberg, Samantha G. and B{\"a}r, Marcus and Ramanathan, Kannan and Heske, Clemens}, title = {Electronic structure of the Zn(O,S)/Cu(In,Ga)Se₂ thin-film solar cell interface}, series = {Progress in Photovoltaics: Research and Applications}, volume = {24}, journal = {Progress in Photovoltaics: Research and Applications}, number = {8}, issn = {1099-159X}, doi = {10.1002/pip.2764}, pages = {1142 -- 1148}, 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{WeinhardtErtanIannuzzietal., author = {Weinhardt, Lothar and Ertan, Emelie and Iannuzzi, Marcella and Weigand, Markus and Fuchs, Oliver and B{\"a}r, Marcus and Blum, Monika and Denlinger, Jonathan D. and Yang, Wooyong and Umbach, Eberhard and Odelius, Michael and Heske, Clemens}, title = {Probing hydrogen bonding orbitals: resonant inelastic soft X-ray scattering of aqueous NH₃}, series = {Physical Chemistry Chemical Physics}, volume = {17}, journal = {Physical Chemistry Chemical Physics}, number = {40}, issn = {1463-9084}, doi = {10.1039/C5CP04898B}, pages = {27145 -- 27153}, 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} }