Characterisation of Thin Films CuIn1-xAlxSe2 Prepared by Selenisation of Magnetron Sputtered Metallic Precursors

Thin films of CuIn1-xAlxSe2 have been produced by the selenisation of magnetron sputtered Cu/In/Al precursor layers using elemental selenium and the chemical and physical properties of the layers have been determined for different conditions of synthesis. For optimum conditions of synthesis it was found possible to produce single phase films with the chalcopyrite structure. These films were pinhole free, had good adhesion and were conformal to the substrate. The films had uniform depth profiles as determined using the MiniSIMS. The layers were highly photoactive, indicating that they have the potential to be used to fabricate thin film photovoltaic solar cell devices

Investigating synthesis of Cu2ZnSn(Se1-x,Sx)4 for values of 0≤x≤1 by S for Se substitution and direct sulphidisation of metallic precursors

Thin layers of Cu2ZnSn(Se1-x,Sx)4 were produced by selenisation and subsequent sulphur substitution of DC sputter-deposited metallic CZT precursors on soda-lime glass. Values of x=(0, 0.07, 0.12, 0.17, 0.28, 1) were measured by EDS. Samples were characterised optically and analysed using the Kubelka-Munk function, and found to have 0.96eV ≤Eg≤ 1.47eV, varying approximately linearly with x. Samples underwent X-ray diffraction characterisation and substituted samples were found to comprise of multiple phase kesterite material with different levels of S substitution, averaging to the values obtained by EDS. The spectra were found to conform to Vegard's law, as peak location shifted linearly between x=0 and x=1. Binary phases are suspected to exist, because of some unusual behaviour at the location of the (200) peak. Lattice parameters for all phases were calculated and found to vary linearly between (a=b=5.692, c=11.338) for x=0 and (a=b= 5.393, c= 10.863) for x=1, which are in excellent agreement with previously published figures

Control of grain size in sublimation-grown CdTe, and the improvement in performance of devices with systematically increased grain size

A method to control the grain size of CdTe thin films deposited by close space sublimation using chamber pressure is demonstrated. Grain diameter is shown to increase in the pressure range 2–200 Torr, following the linear relationship D (?m)=0.027×P (Torr)+0.90. A mechanism is proposed to explain the dominance of the 111 preferred orientation in the small-grained, but not the large-grained films. For a series of CdTe/CdS solar cells in which the only variable was grain size, the performance parameters were seen to increase from 0.54% (0.94 ?m grains) up to a plateau of 11.3% (?3.6 ?m grains). This corresponds to the point at which the series resistance is no longer dominated by grain boundaries, but by the contacts

Formation of Cu(In1-xAlx)Se2 by selenising RF magnetron sputtered Cu/Al/In precursor layers

The fabrication of Cu(In1-xAlx)Se2 using a multi-step process is reported. This process consists of depositing layers of Cu/Al/In, using magnetron sputtering, to form a metallic precursor layer, capping the stack with a layer of selenium, and then annealing in selenium vapour to synthesise the compound. The effects of annealing conditions on the chemical and physical properties of the converted layers were investigated. Rapid thermal processing at different temperatures indicated the formation of Cu(In1-xAlx)Se2 but only for annealing temperatures<360?C; a CuInSe2 phase was found to be present in all the layers fabricated. Annealing processes at higher temperatures (530-550?C) in a large tube furnace did succeed in producing Cu(In1-xAlx)Se2 without CIS, but only when a copper capping layer was included on the precursor stack

A feasibility study towards ultra-thin PV solar cell devices by MOCDV based on a p-i-n structure incorporating pyrite

FeSx layers were deposited onto aluminosilicate glass substrates over a temperature range of 180°C to 500°C using a horizontal AP-MOCVD reactor. Fe(CO)5 was used as the Fe source in combination with t-Bu2S2 or t-BuSH as S precursor to control the rate of reaction and film stoichiometry. The Fe and S partial pressures were kept at 7.5 x 103 and 3.0 mbar, giving a gas phase S/Fe ratio of 400. Reactions followed a non-Arrhenius relationship at higher temperatures. XRD revealed mixed FeSx phases in the layers, which consisted mainly of FeS and Fe1-xS. Post growth annealing of the FeSx films using S powder in a static argon atmosphere and temperatures ranging from 250°C to 400°C was carried out using a 30 minute soak time. Characterisation by XRD confirmed a transitional phase change to FeS2 for the S anneal at 400°C. These films were highly absorbing in the visible region of the solar spectrum, which extended into the NIR. Devices with a p-i-n structure were produced using either a sulphurised or non-sulphurised FeSx i-layer, and compared to p-n devices without an i-layer. A non-sulphurised p-i-n device had the best I-V results, which was attributed to reduced lateral inhomogeneity across the device relative to the thinner p-n device structures. Devices with sulphurised FeSx i-layers performed least efficiently which is suspected to be due to a less defined FeSx/CdS junction caused by severe conditions during the S annealing process

Radio Observations of Super Star Clusters in Dwarf Starburst Galaxies

We present new radio continuum observations of two dwarf starburst galaxies, NGC3125 and NGC5408, with observations at 4.80GHz (6cm) and 8.64GHz (3cm), taken with the Australia Telescope Compact Array (ATCA). Both galaxies show a complex radio morphology with several emission regions, mostly coincident with massive young star clusters. The radio spectral indices of these regions are negative (with alpha ~ -0.5 - -0.7), indicating that the radio emission is dominated by synchrotron emission associated with supernova activity from the starburst. One emission region in NGC5408 has a flatter index (alpha ~ -0.1) indicative of optically thin free-free emission, which could indicate it is a younger cluster. Consequently, in these galaxies we do not see regions with the characteristic positive spectral index indicative of optically obscured star-formation regions, as seen in other dwarf starbursts such as Hen 2-10.Comment: Accepted for publication in MNRA

Annealing studies and electrical properties of SnS-based solar cells

Thin films of SnS (tin sulphide) were thermally evaporated onto glass and CdS/ITO (cadmium sulphide/indium tin oxide) coated glass substrates and then annealed in vacuum with the aim of optimising them for use in photovoltaic solar cell device structures. The chemical and physical properties of the layers were determined using scanning electron microscopy, energy dispersive x-ray analysis, x-ray diffraction, and transmittance versus wavelength measurements. “Superstrate configuration” devices were also made using indium tin oxide as the transparent conductive oxide, thermally evaporated cadmium sulphide as the buffer layer and evaporated copper/indium as the back contact material. Capacitance-voltage data are given for the fabricated devices. Capacitance- voltage, spectral response and I-V data are given for the fabricated devices

Deposition and characterization of copper chalcopyrite based solar cells using electrochemical techniques

Cu(In,Ga)Se2 films were electrodeposited on molybdenum substrates from a single pH buffered bath and annealed in a reducing selenium atmosphere. The opto-electronic properties of the films were characterized using a potentiostatically- controlled three electrode setup and an electrolyte contact. Pulsed illumination was used to determine the carrier type and the speed of photoresponse. Chopped monochromatic illumination was used to measure photocurrent spectra. The electrodeposited copper chalcopyrite films were compared with films prepared by sputtering and spraying techniques

Quaternary Cu2ZnSnSe4 thin films for solar cells applications

Polycrystalline thin films of Cu2ZnSnSe4 (CZTSe) were produced by selenisation of Cu(Zn,Sn) magnetron sputtered metallic precursors for solar cell applications. The p-type CZTSe absorber films were found to crystallize in the stannite structure (a = 5.684 Ã… and c = 11.353 Ã…) with an electronic bandgap of 0.9 eV. Solar cells with the structure were fabricated with device efficiencies up to 3.2%