Jiri Olejnicek

Photoanodes with Fully Controllable Texture: The Enhanced Water Splitting Efficiency of Thin Hematite Films Exhibiting Solely (110) Crystal Orientation.

Hematite, α-Fe2O3, is considered as one of the most promising materials for sustainable hydrogen production via photoelectrochemical water splitting with a theoretical solar-to-hydrogen efficiency of 17%. However, the poor electrical conductivity of hematite is a substantial limitation reducing its efficiency in real experimental conditions. Despite of computing models suggesting that the electrical conductivity is extremely anisotropic, revealing up to 4 orders of magnitude higher electron transport with conduction along the (110) hematite crystal plane, synthetic approaches allowing the sole growth in that direction have not been reported yet. Here, we present a strategy for controlling the crystal orientation of very thin hematite films by adjusting energy of ion flux during advanced pulsed reactive magnetron sputtering technique. The texture and effect of the deposition mode on the film properties were monitored by XRD, conversion electron Mössbauer spectroscopy, XPS, SEM, AFM, PEC water splitting, IPCE, transient photocurrent measurements, and Mott-Schottky analysis. The precise control of the synthetic conditions allowed to fabricate hematite photoanodes exhibiting fully textured structures along (110) and (104) crystal planes with huge differences in photocurrents of 0.65 and 0.02 mA cm(-2) (both at 1.55 V versus RHE), respectively. The photocurrent registered for fully textured (110) film is among record values reported for thin planar films. Moreover, the developed fine-tuning of crystal orientation having a huge impact on the photoefficiency would induce further improvement of thin hematite films mainly if cation doping will be combined with the controllable texture.

Reaction pathway insights into the solvothermal preparation of CuIn 1−x Ga x Se 2 nanocrystalline materials

Reaction pathway investigations of the solvothermal preparation of nanocrystalline CuIn<inf>1−x</inf>Ga<inf>x</inf>Se<inf>2</inf> in triethylenetetramine reveal the early formation of a previously unreported Cu<inf>2−x</inf>Se(s) intermediate. Over 24 hours, this reacts with In and Se species to form CuInSe<inf>2</inf>(s). If Ga is present, the reaction proceeds over an additional 48 hours to form CuIn<inf>1−x</inf>Ga<inf>x</inf>Se<inf>2</inf>. Adding ammonium halide salts reduces the CuInSe<inf>2</inf> formation time to as little as 30 minutes. It is proposed that in these cases, Cu<inf>2−x</inf>Se particle growth is limited via a competitive Cu-halide complex formation. The smaller Cu<inf>2−x</inf>Se particles may react and form CuInSe<inf>2</inf> more rapidly. A reaction pathway scheme consistent with experimental results and previous literature reports is proposed.

Copper-Indium-Boron-Diselenide Absorber Materials

ABSTRACT Attempts to fabricate new CuIn 1-x B x Se 2 (CIBS) and CuBSe 2 (CBS) thin-film materials have been complicated by the formation of interfering crystallites and by the loss of boron from the magnetron sputtered precursor alloys during the selenization and annealing processes. Raman and Auger spectroscopic analysis as well as X-ray diffraction studies show that the formation of boron selenide may be contributing to the difficulty in creating these new materials. INTRODUCTION While much progress has been made in photovoltaic cell development, the United States still does not have a cost-competitive version of a solar cell for domestic or industrial applications except in very remote areas of the country. In order for photovoltaic systems to be competitive, a 15% module efficiency with an installed efficiency of 12% at a cost of

Optical emission spectroscopy of High Power Impulse Magnetron Sputtering (HiPIMS) of CIGS thin films

1/Wp and a 20 year lifetime must be achieved. Broad-based U.S. government-supported research has determined that this goal can most likely be met by thin-film solar cells [1]. Of these thin film materials, the CuInSe

Self organized nanostructures of vapor phase grown CuGaS 2 thin films

CuIn1-xGaxSe2 (CIGS) thin films with x = 0, 0.28 and 1 were prepared by the sputtering of Cu, In and Ga in HiPIMS (High Power Impulse Magnetron Sputtering) or DC magnetron and subsequently selenized in an Ar+Se atmosphere. Optical emission spectroscopy (OES) was used to monitor differences in HiPIMS and DC plasma during sputtering of metallic precursors. Thin film characteristics were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, energy-dispersive X-ray spectroscopy (EDX) and other techniques.

Ex-situ and in-situ selenization of copper-indium and copper-boron thin films

Thin films of nanocrystalline CuGaS2 chalcopyrites have been prepared by chemical vapor transport (CVT) using elements of Cu, Ga, and S with iodine as the transporting agent. Crystalline layers of CuGaS2 have been grown using various iodine concentrations but with constant source materials, growth zones temperatures and growth durations. The films were grown onto sapphire (Al2O3) substrates. The deposits obtained were nanostructures of CuGaS2 thin films and they were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), selected area electron diffraction (SAED), glancing angle X-ray diffraction (GAXRD), X-ray rocking curve, optical, Raman spectroscopy and by photoluminescence (PL) measurements. As-grown different iodine concentration CuGaS2 nanocrystalline thin films have shown p-type conductivity.

A non-vacuum process for preparing nanocrystalline CuIn1−xGaxSe2 materials involving an open-air solvothermal reaction

It has recently been established that the ideal bandgap for terrestrial photovoltaics is 1.37 eV and the bandgap for CuInSe2 is only around 1.04 eV. Thus, a larger bandgap is needed. However, neither the substitution of Ga nor of Al has made a high efficiency solar cell absorber with a band gap of 1.37 eV possible. B, an even smaller atom, should require less atomic substitution than either Ga or Al to achieve a wider bandgap. In order to fabricate a thin film of CuInxB1-xSe2 (CIBS), Cu, In and B were deposited from a variety of sputtering targets which were pure Cu, In, and B; a Cu.45In.55; and a Cu3B2 target. Films were deposited simultaneously and sequentially. After deposition these films were post selenized in another vacuum chamber. Analysis of these films was accomplished using Raman spectroscopy, X-ray diffraction (XRD), and Auger electron spectroscopy (AES). With the difficulties encountered, materials were also deposited in a selenium atmosphere.