ABSTRACT The electronic surface structure of Mo-incorporated WO 3 (“ WO 3: Mo ”) is investigated ... more ABSTRACT The electronic surface structure of Mo-incorporated WO 3 (“ WO 3: Mo ”) is investigated using direct and inverse photoemission and compared to that of pure (Mo-free) WO 3 . The films are found to be n-type with an electronic surface band gap of 3.27 (±0.15) eV. The conduction band minimum (valence band maximum) is 0.64 (±0.10) eV above [2.63 (±0.10) eV below] the Fermi level and at most 0.38 (±0.11) eV above the H +/ H 2 reduction potential [at least 1.66 (±0.11) eV below the H 2 O / O 2 oxidation potential]. The findings suggest an explanation why WO 3: Mo / WO 3 bilayer structures show improved photoelectrochemical performance compared to respective single layer photoanodes.
ABSTRACTThe composition of Cu2ZnSnS4 thin-film solar cell absorbers was varied to induce the.form... more ABSTRACTThe composition of Cu2ZnSnS4 thin-film solar cell absorbers was varied to induce the.formation of secondary impurity phases. For their identification, the samples have been investigated by Cu L3 and S L2,3 soft x-ray absorption (XAS) spectroscopy. We find that Cu L3 XAS is especially sensitive to the presence of copper sulfides as well as copper oxides and/or changes in the electron configuration, suggesting a basis for future studies of the surface, defect, and interface characterization of similar samples. Additionally, it is shown that the S L2,3 absorption data can be used as a very sensitive probe of the variations in the prevalence of S-Zn bonds in the near-surface region of the investigated samples.
At the University of Hawaii (UH), the approach to developing high-efficiency, low-cost photoelect... more At the University of Hawaii (UH), the approach to developing high-efficiency, low-cost photoelectrochemical (PEC) processes for the direct production of hydrogen has included the use of integrated electrochemical/optical models to design photoelectrodes based on multijunction thin-film technology; materials research to identify critical issues on photoelectrode efficiency and stability; and the fabrication and testing of photoelectrodes for optimization and life-testing. In
ABSTRACT The influence of composition on the quaternary Cu2ZnSnS4 (CZTS) absorber material on the... more ABSTRACT The influence of composition on the quaternary Cu2ZnSnS4 (CZTS) absorber material on the secondary phase content, recombination characteristics and solar cell performance is investigated. Best solar efficiencies are found in a very narrow Cu-poor, Zn-rich composition range. Photoluminescence measurements performed at 12 K indicate strong compensation for Cu-poor composition, similar to what is observed in chalcopyrite-type compounds. We find that strongly copper-deficient CZTS contains significant amounts of ZnS, which degrades the solar cell performance.
Titanium has been incorporated in CuInS 2 thin films and devices by diffusion of Ti from the subs... more Titanium has been incorporated in CuInS 2 thin films and devices by diffusion of Ti from the substrate during the CuInS 2 co-evaporation growth process. The CuInS 2 crystal structure is unaffected but the grain size is reduced compared to Ti-free reference samples. X-ray photoelectron spectroscopy shows the presence of TiO 2 at the front of the absorber layer, which appears at the heterojunction interface of the completed CuInS 2 /TiO 2 /CdS/ZnO solar cells. Low temperature photoluminescence spectra show no additional transitions that could be assigned to Ti-based impurity defect levels. Ti-containing cells show conversion efficiencies higher than the Ti-free reference cells due to higher open-circuit voltage (efficiency 11%, V OC ¼ 731 mV). No reduction in short circuit current is detected, indicating that the titanium does not introduce additional bulk recombination. Temperature-dependent current-voltage measurements indicate a reduced interface recombination for cells containing Ti, which is attributed to the TiO 2 interlayer detected by X-ray photoelectron spectroscopy.
ABSTRACT Photoelectrochemical (PEC) water splitting at a semiconductor-electrolyte interface usin... more ABSTRACT Photoelectrochemical (PEC) water splitting at a semiconductor-electrolyte interface using sunlight is of considerable interest as it offers a clean approach to hydrogen production. PEC cells require semiconductor photoelectrode materials fulfilling a number of important requirements, such as band-edge alignment, corrosion resistance to electrolyte, and adequate current generation. We report the development of RF-PECVD-deposited hydrogenated amorphous silicon carbide (a-SiC:H) photoelectrodes with improved durability, which, when combined with a-Si:H tandem photovoltaic devices, should produce hydrogen directly from water under sunlight. The a-SiC:H is commonly grown with a bandgap in excess of 2.0 eV and completes the PEC device by providing contact with the electrolyte, proper band-edge alignment, and acts as a buffer for the a-Si:H tandem structure. Effects of the pH of electrolyte, type of substrates, and a platinum nanoparticle coating on the durability of a-SiC photoelectrodes will be presented. From these studies we surmise that corrosion or damage mechanism occurring on a-SiC:H layer could be divided into different aspects of physical and chemical. From the physical point of view, defects associated with spikes in textured TCO substrates, roughness of stainless steel, or other sources of pinholes may initiate delamination as confirmed by SEM (Scanning Electron Microscopy) and EDS (Energy-Dispersive X-ray Spectroscopy) studies. Chemically, the production of hydrogen involves reactions that may etch the electrode, especially when physical defects are involved. We observe that reducing the acidity of the electrolyte (increasing the pH from 0 to 2) significantly reduces corrosion while the useful photocurrent output of the a-SiC:H p/i structure is unaffected.
... Multijunction. Article Outline. 1. Introduction 2. Experimental 3. Results 3.1. Fe 2 O 3 film... more ... Multijunction. Article Outline. 1. Introduction 2. Experimental 3. Results 3.1. Fe 2 O 3 films 3.2. WO 3 films 3.3. ... films. 3.1. Fe 2 O 3 films. Iron oxide films prepared from eight reactive sputtering runs, designated A through H, were evaluated. ...
... Since the CuIn(1-x)GaxS2 lattice parameter 5 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT can be i... more ... Since the CuIn(1-x)GaxS2 lattice parameter 5 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT can be interpolated from those of CuInS2 and CuGaS2 according to Vegard s rule, the peak shift is attributed to a ... [11] M. B r, W. Bohne, J. Rohrich, E. Strub, S. Lindner, MC ...
ABSTRACT The incorporation of metal impurities M (M=Ti, Fe, or Sn) into CuGaS2 films is investiga... more ABSTRACT The incorporation of metal impurities M (M=Ti, Fe, or Sn) into CuGaS2 films is investigated experimentally as a function of impurity concentration. Films are synthesized by thermal co-evaporation of the elements onto glass/Mo substrates heated to 400°C–570°C. The compositions of the resulting films are measured by energy-dispersive X-ray spectroscopy and the structures of the present phases are studied by X-ray diffraction. The formation of Cu–M–S ternary phases is observed in a wide range of conditions. Films of Cu–Ga–Ti–S, synthesized at 500°C, show the presence of a cubic modification of CuGaS2 and Cu4TiS4. Alloying of CuGaS2 and tetragonal Cu2SnS3 is observed for substrate temperatures of 450°C. A miscibility gap opens at 500°C and above with separate Sn-rich and Ga-rich phases. Similarly, alloys of CuFeS2 and CuGaS2 are only found in Cu–Ga–Fe–S films synthesized at lower substrate temperature (400°C), whereas at 500°C a miscibility gap opens leading to separate Fe-rich and Ga-rich phases.
ABSTRACT The electronic surface structure of Mo-incorporated WO 3 (“ WO 3: Mo ”) is investigated ... more ABSTRACT The electronic surface structure of Mo-incorporated WO 3 (“ WO 3: Mo ”) is investigated using direct and inverse photoemission and compared to that of pure (Mo-free) WO 3 . The films are found to be n-type with an electronic surface band gap of 3.27 (±0.15) eV. The conduction band minimum (valence band maximum) is 0.64 (±0.10) eV above [2.63 (±0.10) eV below] the Fermi level and at most 0.38 (±0.11) eV above the H +/ H 2 reduction potential [at least 1.66 (±0.11) eV below the H 2 O / O 2 oxidation potential]. The findings suggest an explanation why WO 3: Mo / WO 3 bilayer structures show improved photoelectrochemical performance compared to respective single layer photoanodes.
ABSTRACTThe composition of Cu2ZnSnS4 thin-film solar cell absorbers was varied to induce the.form... more ABSTRACTThe composition of Cu2ZnSnS4 thin-film solar cell absorbers was varied to induce the.formation of secondary impurity phases. For their identification, the samples have been investigated by Cu L3 and S L2,3 soft x-ray absorption (XAS) spectroscopy. We find that Cu L3 XAS is especially sensitive to the presence of copper sulfides as well as copper oxides and/or changes in the electron configuration, suggesting a basis for future studies of the surface, defect, and interface characterization of similar samples. Additionally, it is shown that the S L2,3 absorption data can be used as a very sensitive probe of the variations in the prevalence of S-Zn bonds in the near-surface region of the investigated samples.
At the University of Hawaii (UH), the approach to developing high-efficiency, low-cost photoelect... more At the University of Hawaii (UH), the approach to developing high-efficiency, low-cost photoelectrochemical (PEC) processes for the direct production of hydrogen has included the use of integrated electrochemical/optical models to design photoelectrodes based on multijunction thin-film technology; materials research to identify critical issues on photoelectrode efficiency and stability; and the fabrication and testing of photoelectrodes for optimization and life-testing. In
ABSTRACT The influence of composition on the quaternary Cu2ZnSnS4 (CZTS) absorber material on the... more ABSTRACT The influence of composition on the quaternary Cu2ZnSnS4 (CZTS) absorber material on the secondary phase content, recombination characteristics and solar cell performance is investigated. Best solar efficiencies are found in a very narrow Cu-poor, Zn-rich composition range. Photoluminescence measurements performed at 12 K indicate strong compensation for Cu-poor composition, similar to what is observed in chalcopyrite-type compounds. We find that strongly copper-deficient CZTS contains significant amounts of ZnS, which degrades the solar cell performance.
Titanium has been incorporated in CuInS 2 thin films and devices by diffusion of Ti from the subs... more Titanium has been incorporated in CuInS 2 thin films and devices by diffusion of Ti from the substrate during the CuInS 2 co-evaporation growth process. The CuInS 2 crystal structure is unaffected but the grain size is reduced compared to Ti-free reference samples. X-ray photoelectron spectroscopy shows the presence of TiO 2 at the front of the absorber layer, which appears at the heterojunction interface of the completed CuInS 2 /TiO 2 /CdS/ZnO solar cells. Low temperature photoluminescence spectra show no additional transitions that could be assigned to Ti-based impurity defect levels. Ti-containing cells show conversion efficiencies higher than the Ti-free reference cells due to higher open-circuit voltage (efficiency 11%, V OC ¼ 731 mV). No reduction in short circuit current is detected, indicating that the titanium does not introduce additional bulk recombination. Temperature-dependent current-voltage measurements indicate a reduced interface recombination for cells containing Ti, which is attributed to the TiO 2 interlayer detected by X-ray photoelectron spectroscopy.
ABSTRACT Photoelectrochemical (PEC) water splitting at a semiconductor-electrolyte interface usin... more ABSTRACT Photoelectrochemical (PEC) water splitting at a semiconductor-electrolyte interface using sunlight is of considerable interest as it offers a clean approach to hydrogen production. PEC cells require semiconductor photoelectrode materials fulfilling a number of important requirements, such as band-edge alignment, corrosion resistance to electrolyte, and adequate current generation. We report the development of RF-PECVD-deposited hydrogenated amorphous silicon carbide (a-SiC:H) photoelectrodes with improved durability, which, when combined with a-Si:H tandem photovoltaic devices, should produce hydrogen directly from water under sunlight. The a-SiC:H is commonly grown with a bandgap in excess of 2.0 eV and completes the PEC device by providing contact with the electrolyte, proper band-edge alignment, and acts as a buffer for the a-Si:H tandem structure. Effects of the pH of electrolyte, type of substrates, and a platinum nanoparticle coating on the durability of a-SiC photoelectrodes will be presented. From these studies we surmise that corrosion or damage mechanism occurring on a-SiC:H layer could be divided into different aspects of physical and chemical. From the physical point of view, defects associated with spikes in textured TCO substrates, roughness of stainless steel, or other sources of pinholes may initiate delamination as confirmed by SEM (Scanning Electron Microscopy) and EDS (Energy-Dispersive X-ray Spectroscopy) studies. Chemically, the production of hydrogen involves reactions that may etch the electrode, especially when physical defects are involved. We observe that reducing the acidity of the electrolyte (increasing the pH from 0 to 2) significantly reduces corrosion while the useful photocurrent output of the a-SiC:H p/i structure is unaffected.
... Multijunction. Article Outline. 1. Introduction 2. Experimental 3. Results 3.1. Fe 2 O 3 film... more ... Multijunction. Article Outline. 1. Introduction 2. Experimental 3. Results 3.1. Fe 2 O 3 films 3.2. WO 3 films 3.3. ... films. 3.1. Fe 2 O 3 films. Iron oxide films prepared from eight reactive sputtering runs, designated A through H, were evaluated. ...
... Since the CuIn(1-x)GaxS2 lattice parameter 5 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT can be i... more ... Since the CuIn(1-x)GaxS2 lattice parameter 5 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT can be interpolated from those of CuInS2 and CuGaS2 according to Vegard s rule, the peak shift is attributed to a ... [11] M. B r, W. Bohne, J. Rohrich, E. Strub, S. Lindner, MC ...
ABSTRACT The incorporation of metal impurities M (M=Ti, Fe, or Sn) into CuGaS2 films is investiga... more ABSTRACT The incorporation of metal impurities M (M=Ti, Fe, or Sn) into CuGaS2 films is investigated experimentally as a function of impurity concentration. Films are synthesized by thermal co-evaporation of the elements onto glass/Mo substrates heated to 400°C–570°C. The compositions of the resulting films are measured by energy-dispersive X-ray spectroscopy and the structures of the present phases are studied by X-ray diffraction. The formation of Cu–M–S ternary phases is observed in a wide range of conditions. Films of Cu–Ga–Ti–S, synthesized at 500°C, show the presence of a cubic modification of CuGaS2 and Cu4TiS4. Alloying of CuGaS2 and tetragonal Cu2SnS3 is observed for substrate temperatures of 450°C. A miscibility gap opens at 500°C and above with separate Sn-rich and Ga-rich phases. Similarly, alloys of CuFeS2 and CuGaS2 are only found in Cu–Ga–Fe–S films synthesized at lower substrate temperature (400°C), whereas at 500°C a miscibility gap opens leading to separate Fe-rich and Ga-rich phases.
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Papers by B. Marsen