@misc{BaerSongCaballeroetal., author = {B{\"a}r, Marcus and Song, X. and Caballero, R. and Duarte, Roberto Felix and Gerlach, Dominic and Kaufmann, Christian and Schock, Hans-Werner and Wilks, Regan G.}, title = {Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure}, series = {Journal of Applied Physics}, volume = {111}, journal = {Journal of Applied Physics}, number = {3}, issn = {1089-7550}, pages = {034903}, abstract = {Na has deliberately been incorporated into Cu(In,Ga)Se2 ("CIGSe") chalcopyrite thin-film solar cell absorbers deposited on Mo-coated polyimide flexible substrates by adding differently thick layers of NaF in-between CIGSe absorber and Mo back contact. The impact of Na on the chemical and electronic surface structure of CIGSe absorbers with various Cu-contents deposited at comparatively low temperature (420 °C) has been studied using x-ray photoelectron and x-ray excited Auger electron spectroscopy. We observe a higher Nasurface content for the Cu-richer CIGSe samples and can distinguish between two different chemical Na environments, best described as selenide-like and oxidized Na species, respectively. Furthermore, we find a Cu-poor surface composition of the CIGSe samples independent of Na content and — for very high Na contents — indications for the formation of a (Cu,Na)-(In,Ga)-Se like compound. With increasing Nasurface content, also a shift of the photoemission lines to lower binding energies could be identified, which we interpret as a reduction of the downward band bending toward the CIGSe surface explained by the Na-induced elimination of InCu defects.}, language = {en} } @misc{WilksRepinsContrerasetal., author = {Wilks, Regan G. and Repins, Ingrid and Contreras, M. A. and Duarte, Roberto Felix and Herrero-Albillos, J. and Tati-Bismaths, L. and Kronast, F. and Noufi, R. and B{\"a}r, Marcus}, title = {Intergrain variations of the chemical and electronic surface structure of polycrystalline Cu(In,Ga)Se2 thin-film solar cell absorbers}, series = {Applied Physics Letters}, volume = {101}, journal = {Applied Physics Letters}, number = {10}, issn = {0003-6951}, pages = {103908-1 -- 103908-4}, abstract = {The μm-scale spatial distribution of the elements of polycrystalline Cu(In1- x Ga x )Se2 absorber surfaces is examined using x-ray photoelectron emission microscopy. The chemical composition varies from grain to grain, and a direct, linear anticorrelation between the In 3d and Ga 2p photoemission line intensities is observed. The line intensities are interpreted in terms of a varying value of x= Ga/(In+ Ga); the band gaps calculated from the inferred compositions of the grains are shown to be normally distributed with a standard deviation of 40 meV.}, language = {en} } @misc{GerlachWipplerWilksetal., author = {Gerlach, Dominic and Wippler, David and Wilks, Regan G. and Wimmer, Manuel and Lozac'h, Micka{\"e}l and Duarte, Roberto Felix and Ueda, Shigenori and Yoshikawa, Hideki and Lips, Klaus and Rech, Bernd and Sumiya, Masatomo and Kobayashi, Kaoru and Gorgoi, Mihaela and H{\"u}pkes, J{\"u}rgen and B{\"a}r, Marcus}, title = {p-Type a-Si:H/ZnO:Al and μc-Si:H/ZnO:Al Thin-Film Solar Cell Structures—A Comparative Hard X-Ray Photoelectron Spectroscopy Study}, series = {IEEE journal of photovoltaics}, volume = {3}, journal = {IEEE journal of photovoltaics}, number = {1}, issn = {2156-3381}, pages = {483 -- 487}, abstract = {The chemical and electronic properties of a- Si:H(B)/ZnO:Al and μc-Si:H(B)/ZnO:Al thin-film solar cell structures are studied by hard X-ray photoelectron spectroscopy (HAXPES). Using a combination of different X-ray excitation energies and deliberate sample design, we were able to select the probed volume, i.e., the silicon capping layer only or the silicon and zinc oxide layer (including the buried interface). For the a-Si:H(B) material, we find a higher deposition rate and a smaller value for the modified Auger parameter than for μc-Si:H(B). In addition, we find indications of a pronounced band bending limited to the very surface of the a-Si:H(B) and the μc-Si:H(B) layers, which is more distinct in the latter case.}, 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{BaerTheisenWilksetal., author = {B{\"a}r, Marcus and Theisen, J.-P. and Wilks, Regan G. and Erfurth, F. and Duarte, Roberto Felix and Gerlach, Dominic and Haas, S. and Tati-Bismaths, L. and Reinert, F. and Kronast, F. and Niesen, T. P. and Palm, J. and Visbeck, S. and Weinhardt, Lothar}, title = {Lateral inhomogeneity of the Mg/(Zn+Mg) composition at the (Zn,Mg)O/CuIn(S,Se)2 thin-film solar cell interface revealed by photoemission electron microscopy}, series = {Journal of Applied Physics}, volume = {113}, journal = {Journal of Applied Physics}, number = {19}, issn = {1520-8850}, doi = {10.1063/1.4804413}, pages = {193709}, abstract = {Spatial variations in the chemical composition of the (Zn,Mg)O/CuIn(S,Se)2 thin-film solar cell interface were studied by photoemission electron microscopy (PEEM). Energy filtered PEEM images indicate significant differences in the magnesium and zinc distribution. Local photoemission measurements reveal a relative difference in the derived Mg/(ZnþMg) composition of the (Zn,Mg)O material of up to (11.460.7)\%, which can be expected to induce band gap fluctuations of (60630) meV. Furthermore, local areas with significant accumulations of sodium could be observed.}, language = {en} } @misc{GorgoiGerlachWilksetal., author = {Gorgoi, Mihaela and Gerlach, Dominic and Wilks, Regan G. and Wippler, David and Wimmer, Manuel and Lozac'h, Micka{\"e}l and Duarte, Roberto Felix and M{\"u}ck, Leonie Anna and Meier, M. and Ueda, Shigenori and Yoshikawa, Hideki and Lips, Klaus and Rech, Bernd and Sumiya, Masatomo and H{\"u}pkes, J{\"u}rgen and Kobayashi, Kaoru and B{\"a}r, Marcus}, title = {The silicon/zinc oxide interface in amorphous silicon-based thin-film solar cells: Understanding an empirically optimized contact}, series = {Applied Physics Letters}, volume = {103}, journal = {Applied Physics Letters}, number = {2}, issn = {1077-3118}, pages = {023903}, abstract = {The electronic structure of the interface between the boron-doped oxygenated amorphous silicon "window layer" (a-SiOx:H(B)) and aluminum-doped zinc oxide (ZnO:Al) was investigated using hard x-ray photoelectron spectroscopy and compared to that of the boron-doped microcrystalline silicon (μc-Si:H(B))/ZnO:Al interface. The corresponding valence band offsets have been determined to be (-2.87 ± 0.27) eV and (-3.37 ± 0.27) eV, respectively. A lower tunnel junction barrier height at the μc-Si:H(B)/ZnO:Al interface compared to that at the a-SiOx:H(B)/ZnO:Al interface is found and linked to the higher device performances in cells where a μc-Si:H(B) buffer between the a-Si:H p-i-n absorber stack and the ZnO:Al contact is employed.}, language = {en} } @misc{PfrommerAzapiraSteigertetal., author = {Pfrommer, Johannes and Azapira, Anahita and Steigert, Alexander and Olech, Katarzyna and Menezes, Prashanth W. and Duarte, Roberto F{\´e}lix and Liao, Xiaxia and Wilks, Regan G. and B{\"a}r, Marcus and Schedel-Niedrig, Thomas and Driess, Matthias}, title = {Superiorly active and long-term stable nickel-based electrocatalysts for water oxidation in alkaline media based on the ZnO:Ni system}, series = {ChemCatChem}, volume = {9}, journal = {ChemCatChem}, number = {4}, issn = {1867-3899}, doi = {10.1002/cctc.201600922}, pages = {672 -- 676}, language = {en} } @misc{JaeckleLiebhaberNiederhausenetal., author = {J{\"a}ckle, Sara and Liebhaber, Martin and Niederhausen, Jens and B{\"u}chele, Matthias and Duarte, Roberto Felix and Wilks, Regan G. and B{\"a}r, Marcus and Lips, Klaus and Christiansen, Silke}, title = {Unveiling the Hybrid n-Si/PEDOT:PSS Interface}, series = {ACS Applied Materials \& Interfaces}, volume = {8}, journal = {ACS Applied Materials \& Interfaces}, number = {13}, issn = {1944-8244}, doi = {10.1021/acsami.6b01596}, pages = {8841 -- 8848}, language = {en} } @inproceedings{HandickReinhardWilksetal., author = {Handick, Evelyn and Reinhard, Patrick and Wilks, Regan G. and Pianezzi, Fabian and Duarte, Roberto Felix and Gorgoi, Mihaela and Kunze, Thomas and B{\"u}cheler, Stephan and Tiwari, Ayodhya N. and B{\"a}r, Marcus}, title = {NaF/KF post-deposition treatments and their influence on the structure of Cu(In,Ga)Se₂ absorber surfaces}, series = {IEEE 43rd Photovoltaic Specialists Conference (PVSC), 5-10 June 2016}, booktitle = {IEEE 43rd Photovoltaic Specialists Conference (PVSC), 5-10 June 2016}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-5090-2724-8}, doi = {10.1109/PVSC.2016.7749400}, pages = {17 -- 21}, language = {en} } @phdthesis{Duarte, author = {Duarte, Roberto Felix}, title = {Analysis and optimization of interfaces in "wide-gap" chalcopyrite-based thin film solar cell devices}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-37402}, pages = {238}, abstract = {The chemical and electronic structure of chalcopyrite absorbers with different bulk band gap energies, Egbulk, [i.e., low-gap Cu(In,Ga)Se2 (CIGSe, Egbulk ~ 1.2 eV) and wide-gap CuInS2 (CIS, Egbulk ~ 1.5 eV)] and of buffer/absorber heterointerfaces based on these materials are studied with soft and hard x-ray spectroscopy techniques. Mechanisms that benefit (limit) the performance of low(wide)-gap chalcopyrite-based solar cells are identified. This knowledge is used to develop surface tailoring treatments to optimize buffer/absorber heterointerfaces based on wide-gap chalcopyrites and improve the performance of their solar cells. Photoemission spectroscopy (PES) characterization of the two absorbers (i.e., CIGSe and CIS) reveal compositional-depth profiles. The changes detected in CIGSe include: a near surface Ga-depletion, a strongly Cu-poor surface and a strong presence of surface Na that (likely) occupies Cu vacancies. A similar Cu-deficiency is found in CIS. The depth-composition changes result in significant widening of the band gap at the surface, Egsurf, (i.e., CIGSe, Egsurf: 1.70 ± 0.2 eV and CIS, Egsurf: 1.88 ± 0.2 eV) as evident by ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) measurements. Differences in the interaction of the CIGSe and CIS surfaces with deposited buffer materials are identified. PES and modified Auger parameter studies reveal strong intermixing at the CdS/CIGSe and ZnS/CIGSe heterointerfaces. S L2,3 x-ray emission spectroscopy (XES) measurements of CIGSe substrates submitted to CdS chemical bath deposition (CBD-CdS) treatments show the formation of In2S3 and defect-rich/nanostructured CdS at the interface, compounds with higher band gap values than the measured Egsurf for CIGSe. S L2,3 XES spectra of CIGSe substrates submitted to CBD-ZnS treatments reveal the formation of (Zn,In)(S,Se)2 chemical analogs at the interface. PES and XES measurement series show that the CdS/CIS heterointerface is more abrupt, with no detected interface chemical species. Direct measurement of the band alignment of these heterointerfaces reveals: an ideal conduction band offset (CBO) configuration for CdS/CIGSe (i.e., CBO: +0.11 ± 0.25 eV), a spike CBO configuration for ZnS/CIGSe (i.e., CBO: +1.06 ± 0.4 eV), and a highly unfavorable cliff CBO configuration for CdS/CIS (i.e., CBO: -0.42 ± 0.25 eV). The performance of solar cell devices based on these heterointerfaces is correlated to their CBO configuration. Two surface tailoring approaches intended to correct the CBO configuration of the CdS/CIS heterointerface are presented. One method is based on rapid thermal processing (RTP) selenization treatments of CIS absorbers, aiming to exchange Se for S in treated samples. The idea behind this approach is to modify the surface of a wide-gap chalcopyrite so that it forms a more favorable heterointerface with CdS, such as heterointerfaces within low-gap chalcopyrite devices. X-ray fluorescence analysis and PES measurements of RTP-treated CIS samples show a greater treatment effect at the surface of the sample compared to the bulk (i.e., surface [Se]/[S+Se] range: 0.23 ± 0.05 to 0.83 ± 0.05, compared to bulk [Se]/[S+Se] range: 0.01 ± 0.03 to 0.24 ± 0.03). Tuning of the Cu:In:(S+Se) surface composition from a Cu-poor 1:3:5 to a 1:1:2 stoichiometry is observed in RTP-treated CIS samples with lower to higher surface Se contents, respectively. UPS measurements show a shift in valence band maximum toward the Fermi level in samples with higher surface Se content (i.e., -0.88 ± 0.1 to -0.51 ± 0.1 eV), as expected for a reduction in Egsurf due to exchange of Se for S. Ultraviolet-visible spectrophotometry reveals a reduction in the optical band gap of samples with greater Se incorporation (i.e., from 1.47 ± 0.05 to 1.08 ± 0.05 eV), allowing for a working window for optimization purposes. The second tailoring method involves surface functionalization of CIS absorbers with dipole-charge-inducing self-assembled monolayers (SAM) of benzoic acid derivatives and thiol molecules. The introduction of dipole charges between a heterointerface can tune the relative alignment of the electronic bands composing its electronic structure; thus, use of a suitable dipole-inducing SAM could correct the CBO misalignment in the CdS/CIS heterointerface. UPS measurements of the secondary electron cut-off region of CIS samples treated with a selected set of SAMs show a work function modulation of CIS (i.e., 4.4 ± 0.2 eV - 5.2 ± 0.2 eV). Small gains in solar cell parameters of solar cells based on SAM-modified heterointerfaces are measured. An overview of the performance of chalcopyrite(kesterite)-based solar cells in relation to the electronic properties of their corresponding buffer/absorber heterointerface suggests that optimization approaches extending beyond the buffer/absorber heterointerface may be needed for further performance gains in wide-gap chalcopyrite-based solar cell devices.}, 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{CaoJaftaGongetal., author = {Cao, Jie and Jafta, Charl J. and Gong, Jiang and Ran, Qidi and Lin, Xianzhong and Duarte, Roberto Felix and Wilks, Regan G. and B{\"a}r, Marcus and Yuan, Jiayin and Ballauff, Matthias and Lu, Yan}, title = {Synthesis of Dispersible Mesoporous Nitrogen-Doped Hollow Carbon Nanoplates with Uniform Hexagonal Morphologies for Supercapacitors}, series = {ACS Applied Materials \& Interfaces}, volume = {8}, journal = {ACS Applied Materials \& Interfaces}, number = {43}, issn = {1944-8244}, doi = {10.1021/acsami.6b08946}, pages = {29628 -- 29636}, language = {de} }