21 research outputs found
Properties of Al-doped ZnS films grown by chemical bath deposition
No full textZinc sulphide (ZnS) buffer layers are a cadmium free, wider energy band gap, alternative to the cadmium sulphide(CdS) buffer layers commonly used in copper indium gallium diselenide (CuInGaSe2)-based solar cells. However extrinsic doping of the ZnS is important to lower the resistivity of the layers and to improve flexibility of device design. In this work, Al-doped ZnS nanocrystalline films have been produced on glass substrates using a chemical bath deposition (CBD) method. The Al- concentration was varied from 0 at. % to 10 at. %, keeping other deposition parameters constant. The elemental composition of a typical sample with 6 at. % ‘Al’ in ZnS was Zn=44.9 at. %, S=49.8 at. % and Al=5.3 at.%. The X-ray diffraction data taken on these samples showed a broad peak corresponding to the (111) plane of ZnS while the crystallite size varied in the range, 8 – 15 nm, depending on the concentration of Al in the layers. The films with a Al-doping content of 6 at. % had an optical transmittance of 75 % in the visible range and the energy band gap evaluated from the data was 3.66 eV. The films n-type electrical conductivities and the electrical resistivity varied in the range, 107-103 Ωcm, it decreasing with an increase of the Al-concentration in the solution
Nano-Photonic Structures for Light Trapping in Ultra-Thin Crystalline Silicon Solar Cells
No full textThick wafer-silicon is the dominant solar cell technology. It is of great interest to develop ultra-thin solar cells that can reduce materials usage, but still achieve acceptable performance and high solar absorption. Accordingly, we developed a highly absorbing ultra-thin crystalline Si based solar cell architecture using periodically patterned front and rear dielectric nanocone arrays which provide enhanced light trapping. The rear nanocones are embedded in a silver back reflector. In contrast to previous approaches, we utilize dielectric photonic crystals with a completely flat silicon absorber layer, providing expected high electronic quality and low carrier recombination. This architecture creates a dense mesh of wave-guided modes at near-infrared wavelengths in the absorber layer, generating enhanced absorption. For thin silicon (<2 μm) and 750 nm pitch arrays, scattering matrix simulations predict enhancements exceeding 90%. Absorption approaches the Lambertian limit at small thicknesses (<10 μm) and is slightly lower (by ~5%) at wafer-scale thicknesses. Parasitic losses are ~25% for ultra-thin (2 μm) silicon and just 1%–2% for thicker (>100 μm) cells. There is potential for 20 μm thick cells to provide 30 mA/cm2 photo-current and >20% efficiency. This architecture has great promise for ultra-thin silicon solar panels with reduced material utilization and enhanced light-trapping
Thin Films of Tin Sulphide for Application in Photovoltaic Solar Cells
No full textTin sulphide (SnS) is a promising new material for use in photovoltaic solar cells. With a direct energy band gap of about 1.3 eV, and a high optical absorption coefficient, only a few microns of SnS are needed to absorb most of the incident light. Not only is SnS made of abundant, environmentally acceptable elements, it is also amphoteric giving flexibility to device design. Structures that can be envisioned include p-type SnS (absorber layer) / n-type (window layer) heterojunction devices, buried p-n junction devices made using SnS and p-i-n structure devices where the i-layer is SnS. It is most likely that the grain boundaries in SnS can be passivated either by counter-doping the grain boundaries, or by oxidizing the grain boundaries to form wide energy bandgap n-type SnO2 within p-type SnS, as dopants or oxygen will diffuse preferentially down the grain boundaries and react first at the grain boundary surfaces. Thin film solar cell devices based on the use of SnS have now been produced with efficiencies > 2 %; these and other promising results indicate that it is most likely that devices with efficiencies > 10% will be produced in the near future. Given that tin layers are routinely coated in industry over large area substrates and that industrial sulphidization processes are also well established, the industrialization of this technology should be more straightforward than that encountered with the already commercialised cadmium telluride and copper indium gallium diselenide thin film technologies. This review discusses the chemical and physical properties of SnS, the methods of producing both bulk crystals and thin films of SnS, the literature available on studies of SnS2 based photovoltaic solar cell devices, and progress made so far in developing this exciting new material
Aluminum-Induced crystallization: Applications in photovoltaic technologies
No full text[No abstract available
Virtual Referee: A system to identify off- sides in Football
No full textThe off-side rule is the most complicated rule in soccer. Today, off-sides are determined with the help of referees running on the sides of the field or with the help of cameras. However, for lower league games the installation of a camera based system is very expensive. This work proposes a sensor based system that can be worn by players which can automatically detect off-sides. In order to create such a system, two aspects had to be researched (a) localisation and (b) ball detection. This work provides an evaluation of an ultra-wide band system in outdoor conditions to solve the localisation problem and various proximity based sensors to solve the ball detection problem. The primary research objective of this work was to find the pit-falls of the ultra-wide band system with respect to our application. It was found that the tri-lateration algorithm implemented on the devices contributed to a lot of errors in localisation accuracy and the overall system suffered from significant packet loss. A custom tri-lateration algorithm along with hardware improvements are proposed. Our results show that the localisation errors are reduced by 56 % and improved system suffers from nearly no packet loss. As for ball detection, results show that ToF sensors provided the best accuracy in detecting the ball.Electrical Engineering | Embedded System
Influence of growth rate on microstructure and optoelectronic behaviour of ZnS films
No full textNanocrystalline ZnS films have been grown on glass substrates by close spaced evaporation at various deposition rates, with a constant substrate temperature of 300 °C. The x-ray photoelectron spectroscopy studies revealed that nearly stoichiometric ZnS layers were grown at deposition rates in the range 20–30 Å s−1. The x-ray diffraction data confirmed the cubic structure of ZnS films for all the deposition rates. The surface morphological studies were made using an atomic force microscope, which indicated a rough surface and that the roughness increases with the deposition rate. The optical analysis showed that the layers grown at a deposition rate of 30 Å s−1 exhibited the highest optical transmittance of 82%. The optical band gap of the films varied in the range 3.63–3.54 eV with the change in the deposition rate. The effect of the rate of deposition on the photoluminescence characteristics was also studied, which showed an increase in luminescence intensity with the decrease in the particle size. The electrical properties of the layers were highly influenced by the deposition rate. The temperature dependence of electrical conductivity was measured and the activation energies were also evaluated
Thickness dependence of structure and optoelectronic properties of In2O3:Mo films prepared by spray pyrolysis
No full textThe influence of thickness on the structural, morphological and optoelectronic behavior of Mo-doped In2O3 films, prepared by spray pyrolysis was investigated. The films had the cubic crystal structure for all the thicknesses investigated although it was found that a change in the preferred orientation and growth mode, from 2D to 3D, has occurred with an increase of film thickness. A small degradation in the optical transmittance has been observed with the increase of film thickness. The variation of electrical resistivity, mobility and charge carrier concentration with film thickness were also studied and the results discussed
