Scott A. Darveau

Air Stable, Photosensitive, Phase Pure Iron Pyrite Nanocrystal Thin Films for Photovoltaic Application

Iron pyrite (FeS(2)) is a naturally abundant and nontoxic photovoltaic material that can potentially make devices as efficient as silicon-based ones; however existing iron pyrite photovoltaic devices contain thermodynamically unstable FeS(2) film surfaces that lead to low open circuit voltages. We report the rational synthesis of phase pure, highly crystalline cubic FeS(2) nanocrystals (NCs) using a trioctylphosphine oxide (TOPO) assisted hot-injection method. The synthesized pyrite NC films have excellent air stability over one year. In contrast, obvious surface decomposition was observed on the surface of FeS(2) NCs synthesized without TOPO. A high carrier mobility of 80 cm(2)/(V s) and a strong photoconductivity were observed for the first time for pyrite films at room temperature. Our results indicate that TOPO passivates both iron and sulfur atoms on FeS(2) NC surfaces, efficiently inhibiting surface decomposition.

Zinc alloyed iron pyrite ternary nanocrystals for band gap broadening

Iron pyrite (FeS2) is one of the most promising photovoltaic materials with high natural abundance and low cost but with a lower-than-optimum band gap of 0.95 eV. Here the feasibility of band gap broadening was explored by zinc alloying of FeS2 nanocrystals (NCs). A significant amount of zinc up to 6 at%, 30 times higher than previously reported, was incorporated into the FeS2 NCs. In contrast to band gap bowing predicted by first-principles calculations, a band gap enlargement of ∼0.1 eV was observed by zinc alloying. A more than five-times reduction of dark current in the zinc alloyed FeS2 photoconductor was observed and should ascribe to the increased band gap.

Chemical bath deposition (CBD) of iron sulfide thin films for photovoltaic applications, crystallographic and optical properties

A low temperature chemical deposition method has been developed to deposit iron/sulfur thin films onto soda lime glass substrates. The chemical bath deposition (CBD) consists of aqueous solution ferrous sulphate, disodium salt of ethylenediaminetetra-acetic acid (Na2EDTA), sodium thiosulphate and organic solutions of ethylenediamine and methanol. The experiments were performed at room temperature and under two different conditions. The films were uniform and adhered well to the soda lime glass substrates. The deposited films were additionally processed in a sulfur and nitrogen atmosphere at a variety of different temperatures to form the pyrite phase of FeS2. The as-deposited and annealed thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical absorption, auger electron spectroscopy (AES), and resistivity. The optimization of the FeS2 pyrite growth parameters was determined using XRD. Although both methods appeared to form FeS2 the second method is the preferable one where additional sulfurization at 450 °C for one hour yielded the films with the maximum crystalline order and stoichiometry.

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

Preparation of CIGS thin films by HiPIMS or DC sputtering and various selenization processes

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.

A novel sol-gel route to pinhole-free iron sulfide thin films

Abstract CuIn1-xGaxSe2 (CIGS) thin films were prepared by the sputtering of metallic precursors Cu, In, Ga in HiPIMS (High Power Impulse Magnetron Sputtering) or DC magnetron and subsequently selenized in an atmosphere of pure Se or Ar+Se. The average absorbed power and discharge current were the same in the HiPIMS and DC plasma. The basic aim of this work was to compare the structural properties of the CIGS films as a function of magnetron excitation mode and selenization thermal treatment conditions. Film characteristics were measured using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy and other techniques. All the CIGS films revealed the chalcopyrite crystal structure with a preferential (112) orientation. Only a very small influence of magnetron excitation mode on thin film properties was observed. On the other hand, selenization in Ar+Se atmosphere led to bigger grain size, better crystallinity and a significantly higher level of Ga substitution.

Self organized nanostructures of vapor phase grown CuGaS 2 thin films

The general purpose of the study is to fabricate and improve upon FeS2 thin films which can be used as the photon absorber layer for a heterojunction or homojunction solar cell. This work deals with the preparation of the pyrite by an unconventional sol-gel approach. Thin pyrite films were prepared by sulfurizing the iron oxide films previously deposited through the sol-gel method using iron (III) chloride as a precursor. The structural, morphological, electronic and optical properties of the deposited films were determined using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, Auger electron spectroscopy (AES), UV-Vis absorption spectroscopy, Hall effect and profilometry. The effects of annealing and sulfurization temperatures were studied. The work was also devoted to the research of sodium diffusion from the substrate due to the thermal treatment and its affect on the pyrite films functionality.

Problems with Synthesis of Chalcopyrite CuIn1-xBxSe2

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.