• Energy Research

This work has been focused on the synthesis by co-evaporation on bare and Mo-coated glass substrates of tin sulfide films with thicknesses in the 700-1200 nm range for use as absorber layers, with a substrate temperature at 350 ??C and a sulfur partial pressure of 1-2*10-3 Pa. After evaporation, the samples were heated at 500 ??C under Ar atmosphere. The evolution of the morphological, structural, chemical and optical properties of the samples deposited on bare or Mo-coated glass substrates has been analyzed as a function of the thickness, before and after annealing. For the samples grown on bare glass, some phase mixing has been observed by X-ray diffraction (XRD). Samples with reduced thickness preferably crystallize in the SnS phase, whereas thicker layers crystallize in the Sn2S3 phase. Otherwise, the Mo-coated glass substrate favors the crystallinity in the phase SnS preferably. Scanning electron microscope (SEM) shows thin films with homogeneous and uniform surface. All samples were characterized by reflectance (R) and transmittance (T) measurements in the wavelength range 300-1500 nm, showing an increase of the maxima of reflectance when the films are obtained on bare glass and after annealing. The energy band gap values, calculated from optical measurements of T and R, are between 1.14-1.20 eV, being suitable for absorbers layers in photovoltaic applications.

ABSTRACTIn this work, Cu and In thin films, as precursors for CuInSe2 (CIS) formation, have been deposited on glass substrate up to 30 × 30 cm2 area using an electron beam evaporator in sequential processes. In order to obtain a similar global composition, three types of sequential processes of evaporation: A) Cu/In/Cu/In, B) Cu/In/Cu/In/Cu/In and C) In/Cu/In/Cu have been tested. As-grown thin films were studied at room temperature and after 120° C annealing. XRD analysis of these films showed mainly the CuIn2−x (0≤ × ≤ 1) phase at room temperature, and Cu11In9 after annealing at 120° C. After alloying, the films were selenized at temperature between 250° and 400° C in vacuum using elemental selenium vapour. XRD of the selenized thin films corresponding to In/Cu/In/Cu sequence and previously annealing at 120° C, showed the major presence of the polycrystalline chalcopyrite structure CuInSe2 with preferential orientation (112) plane at temperature as low as 250° C. From SEM studies and profilometer measurements a decrease in the mean roughness could be observed after annealing at 120° C. In contrast the resistivity of the films increased.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Abstract The development of wide-bandgap materials deposited on transparent conducting oxides for high efficiency and low cost semitransparent photovoltaic devices or tandem cells is becoming important in the last few years. CuIn1−xAlxSe2 (CIAS) thin films with bandgap above 1.95 eV for 0.7≤x≤0.9 were deposited onto bare and two different (tin-doped indium oxide, ITO and aluminium-doped zinc oxide, AZO) coated glass substrates by a two stage process consisting of the selenization of metallic precursor layers. Polycrystalline CIAS thin films orientated preferentially along the (1 1 2) plane with chalcopyrite structure were obtained. The bandgap energy increased no linearly with the Al addition. X-ray diffractograms showed the coexistence of several CIAS phases. Optical, structural and composition analysis revealed that the ITO and AZO substrates promote not only the incorporation of Se, but also a more homogenous distribution in depth regarding the CIAS samples on bare glass, and acted like a barrier to the oxidation from the glass substrate.

Abstract Antimony doped tin oxide (ATO) is a transparent conducting oxide (TCO), which has been the focus of intensified study due to its wide range of technological applications and low cost. In the present work ATO films have been prepared by reactive DC magnetron sputtering from a metallic target at different discharge power densities without direct substrate heating. Then a post-deposition annealing at 350 °C in N2 during 20 min was performed. There is a process window for the optimal sputter deposition of ATO with a minimum resistivity of about 3.3×10−3 Ω cm observed in samples deposited at a power density of 1.13 W/cm2. These samples, which present a (2 1 1) preferential orientation, have good electrical conductivity and good transparency in the visible range. Higher values of sputtering discharge power density (1.24 W/cm2) change the preferential orientation to (1 0 1) because of the formation of oxygen vacancy planes. These samples are less conductive and transparent because their layered structure reduces the free charge mobility and allows the formation of Sb in its unusual oxidation state 4+ (between Sb3+ and Sb5+), which produces a sample blue darkening. Higher discharge power densities, above 1.41 W/cm2, produce amorphous samples and an abrupt resistivity increase. The aim of the present work is to go into more depth in the knowledge of ATO in order to develop thin films with optimal electrical and optical properties.

Cu, In and Se have been codeposited in thin films by potentiostatic one-step electrodeposition. The as-deposited material has shown direct optical transitions attributable to the CuInSe2 semiconductor, but also additional absorption corresponding to another semimetallic phase. The secondary phases are selenium and copper selenide compounds which have been determined by composition measurements. In order to eliminate the semimetallic phases and to improve the semiconductor behaviour of the electrodeposited material, thermal and chemical treatments have been performed. After heat-treatment of the samples at 400°C in flowing argon, elemental selenium loss has been detected together with an enhancement of the allowed direct optical transition. The subsequent chemical etching of the layers in a KCN solution has showed to be successful in eliminating the copper selenide phases which were responsible of the remaining sub-bandgap absorption.

Abstract The combination of electrodeposited Cu–Se alloy and sputtered In precursors, followed by annealing in Se atmosphere, was found successful to obtain CuInSe2 thin films with Cu/In composition ratios varying between 0.25 and 2.75. Structural and morphological properties were observed to be dependent on annealing temperature and Cu/In ratio. When Cu/In>1, both a CuInSe2 crystallinity improvement and a smooth surface were achieved. Apart from the ternary CuInSe2, two different binaries were detected: Cu2Se crystallises after 400°C annealing in samples with Cu/In>1, and In2Se3 does after annealing at 500°C for the distinct Cu/In ratios were considered.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Abstract Transparent conducting oxides (TCOs) have a wide range of applications in several optoelectronic devices but beyond the conventional characteristics of transparency and conductivity different characteristics are required by each different technology. This constitutes a promising stimulation of the present research of TCO films. In order to investigate the possible application of antimony doped tin oxide (ATO) thin films as a TCO electrode for new concepts in solar cells and other optoelectronic devices, ATO thin films with adequate properties in terms of light transparency and conductivity were obtained using room temperature processes by oxygen-reactive DC magnetron sputtering, then the films were annealed in nitrogen atmosphere at a temperature of 350 °C. The effect of O 2 /(Ar+O 2 ) ratio in the sputter flow gas mixture has been studied. Results regarding to optical and electrical properties, microstructure and composition measurements are reported.