Enhancement of photovoltaic properties of multicrystalline silicon solar cells by combination of buried metallic contacts and thin porous silicon

Photovoltaic properties of buried metallic contacts (BMCs) with and without application of a front porous silicon (PS) layer on multicrystalline silicon (mc-Si) solar cells were investigated. A Chemical Vapor Etching (CVE) method was used to perform front PS layer and BMCs of mc-Si solar cells. Good electrical performance for the mc-Si solar cells was observed after combination of BMCs and thin PS films. As a result the current-voltage (I-V) characteristics and the internal quantum efficiency (IQE) were improved, and the effective minority carrier diffusion length (Ln) increases from 75 to 110 μm after BMCs achievement. The reflectivity was reduced to 8% in the 450-950 nm wavelength range. This simple and low cost technology induces a 12% conversion efficiency (surface area = 3.2 cm²). The obtained results indicate that the BMCs improve charge carrier collection while the PS layer passivates the front surface.     

Influence of the layer thickness and hydrogen dilution on electrical properties of large area amorphous silicon p–i–n solar cell

The aim of this work is to present data concerning the optimization of performances of a large area amorphous silicon p–i–n solar cell (30×40 cm²) deposited by plasma enhanced chemical vapour deposition (PECVD) at 27.12 MHz. In this work the solar cell was split into small areas of 0.126 cm², aiming to study the device performance uniformity, where emphasis was put on the role of the n-layer thickness. The solar cells were studied through the spectral response behaviour in the 400–750 nm range as well as by the behaviour of the AC impedance. Solar cells with fill factor of 0.58, open circuit voltage of 0.83 V, short circuit current density of 17.14 mA/cm² and an efficiency of 8% were obtained at growth rates higher than 0.3 nm/s.     

ZnO-based nanocrystalline powders with applications in hybrid photovoltaic cells

In recent years there has been a growing interest in the development of hybrid photovoltaic cells consisting of new materials, such as devices based on the combination of a wide gap semiconductor and an organic dye (dye-sensitized solar cells, DSSC). In this paper we obtain nano-zinc oxide particles whose optical and electrical properties have been modified by the presence of small amounts of Al or In acting as dopants. The aim of this study is to improve the compatibility of each of the compounds present in the photovoltaic solar cell. The knowledge gained will provide input to guide the processes in the manufacture of hybrid solar cells.     

An overview of silicon ribbon growth technology

A silicon ribbon growth method, String Ribbon, is discussed and compared with the two other vertical ribbon technologies. Manufacturing advances in production of 300 μm String Ribbon are described along with characterization of this ribbon, particularly dislocation distribution. Progress on the growth of 100 μm ribbon and in the making of higher efficiency cells are detailed.     

Load independent efficient,transformerless inverter for photovoltaic applications

The overall efficiency of photovoltaic power systems (PVPS) depends on the efficiency of the PV panels, the storage batteries, and the efficiency of the inverter circuitry. The last is greatly influenced by the connected load, as the efficiencies are severly reduced when operating at low loads. This is especially effective when the PVPS is most likely to operate with a fraction of the full load. The suggested inverter has excellent efficiency characteristics over a wide power range, and because it contains only electronic components further cost reduction can be expected. Experimentally this inverter is designed for a 120 W output using thyristor switching devices; the efficiency obtained is 88% at full load and 85.2% at 10% of full load, with a maximum output voltage of 60 V stepped sinewave with frequency of 50 Hz. However, higher power outputs could also be achieved with this type of inverter.     

Germanium-doped Czochralski silicon for photovoltaic applications

Germanium (Ge)-doped Czochralski (GCZ) silicon has been grown for photovoltaic (PV) applications. It is found that Ge doping improves the mechanical strength of CZ silicon, resulting in the reduction of breakage during wafer cutting, cell fabrication and module assembly. Boron-oxygen (B-O) defects that lead to the light-induced degradation (LID) of carrier lifetime are effectively suppressed by Ge doping. The decrease in the maximum concentration of B-O defects increases with an increase of Ge concentration. The efficiency of GCZ silicon solar cells and the power output of corresponding PV modules both exhibit smaller loss under sunlight illumination. The current work suggests that GCZ silicon should be potentially a novel substrate for thin solar cells with low LID effect.     

Solar photovoltaic electricity: Current status and future prospects

We review the technical progress made in the past several years in the area of mono- and polycrystalline thin-film photovoltaic (PV) technologies based on Si, III-V, II-VI, and I-III-VI₂ semiconductors, as well as nano-PV. PV electricity is one of the best options for sustainable future energy requirements of the world. At present, the PV market is growing rapidly at an annual rate of 35-40%, with PV production around 10.66 GW in 2009. Si and GaAs monocrystalline solar cell efficiencies are very close to the theoretically predicted maximum values. Mono- and polycrystalline wafer Si solar cells remain the predominant PV technology with module production cost around $1.50 per peak watt. Thin-film PV was developed as a means of substantially reducing the cost of solar cells. Remarkable progress has been achieved in this field in recent years. CdTe and Cu(In,Ga)Se₂ thin-film solar cells demonstrated record efficiencies of 16.5% and almost 20%, respectively. These values are the highest achieved for thin-film solar cells. Production cost of CdTe thin-film modules is presently around $0.76 per peak watt.     

Mechanical effects of chemical etchings on monocrystalline silicon for photovoltaic use

The mechanical effects of two etching treatments commonly applied on silicon wafers for the PV industry, are considered. The failure characteristics of this material under concentrated load are shown . In both cases, the maximum elongation and sustainable load of the etched wafers were measured to be higher than those of the original sample. The employed experimental procedure and results are presented here and a statistical data analysis substantiates the results observed. An attempt of explanation for this effect is offered based on the removal of a shallow highly defective layer induced by the etching of the material.     

Solar grade silicon feedstock supply for PV industry

For the growth of the photovoltaic industry, it seems inevitable to create an independent feedstock supply with solar grade high-purity silicon, because the availability of the hitherto used by-products in the electronic silicon industry is limited and will not increase reasonably within the next 10–15 years.One of the results of the study “Present and likely future bottlenecks analysis for a sustainable photovoltaic policy” carried out by Bayer and Life, within EPIA, sponsored by the European Commission, within the ALTENER programme, shows that the feedstock used to date, based on electronic grade silicon Scraps is already limiting the PV market expansion even if a true shortage is not expected before 2004–2005 according to a “low growing PV market scenario”. This conclusion implies that a new silicon feedstock not depending on electronic grade silicon production chain must be available on the market from the years 2004 to 2005.Bayer evaluated different ways for the production of solar grade silicon with a capacity of upto 5000 mt/yr. By calculating different routes, it seems possible to install a 5000 t plant by an investment of 110 Mio. Euro and to sell silicon feedstock with a price level of 12–15 Euro/kg. Bayer has been developing a suitable process and the new owner, the Deutsche Solar GmbH, is considering what effort is necessary for a pilot production plant.The feedstock situation is discussed under the aspect of availability of different materials and the efforts under consideration by different parties.     

Applications of carbon materials in photovoltaic solar cells

Carbon-based photovoltaic cells (PVCs) have attracted a great deal of interest for both scientific fundamentals and potential applications. In this paper, applications of various carbon materials in PVCs, especially in silicon-based solar cells, organic solar cells and dye-sensitized solar cells, are reviewed. The roles carbon materials played in the PVCs are discussed. Further research on solar cells comprised solely of carbon is prospected.     

Low temperature polycrystalline silicon: a review on deposition, physical properties and solar cell applications

This review article gives a comprehensive compilation of recent developments in low temperature deposited poly Si films, also known as microcrystalline silicon. Important aspects such as the effect of ions and the frequency of the plasma ignition are discussed in relation to a high deposition rate and the desired crystallinity and structure. The development of various ion energy suppression techniques for plasma enhanced chemical vapour deposition and ion-less depositions such as HWCVD and expanding thermal plasma, and their effect on the material and solar cell efficiencies are described. The recent understanding of several important physical properties, such as the type of electronic defects, structural effects on enhanced optical absorption, electronic transport and impurity incorporation are discussed. For optimum solar cell efficiency, structural considerations and predictions using computer modelling are analysed. A correlation between efficiency and the two most important process parameters, i.e., growth rate and process temperature is carried out. Finally, the application of these poly Si cells in multijunction cell structures and the best efficiencies worldwide by various deposition techniques are discussed.     

Explicit model of photovoltaic panels to determine voltages and currents at the maximum power point

A simple explicit photovoltaic formulation for characterizing and dimensioning cell-arrays is presented. The method permits the short-circuit current, the open-circuit voltage, the maximum cell power and the optimum cell-operation conditions to be determined. Further, the model also allows quantifying the effects of panel temperature and solar irradiance on key cell parameters. Based on several datasheets, the methodology is validated by covering a wide range of operation conditions. The proposed approach can thus, be very useful for design engineers to quickly and easily determine the performance of any photovoltaic array without performing tedious numerical calculations.     

Australian educational and research opportunities arising through rapid growth in the photovoltaic industry

In recent years, the photovoltaic (PV) industry has been growing rapidly at the rate of 30–40% per annum. As a result of this rapid growth, new opportunities through collaborative research with industry and in the educational area have arisen. To address these needs, the Australian government, through the Australian Research Council (ARC), has established a Key Centre for Teaching and Research in Photovoltaic Engineering at the University of New South Wales (UNSW). This is one of only eight such centres established Australia-wide across all disciplines. The primary new initiative of this Key Centre is to establish the world's first undergraduate engineering degree in photovoltaics and solar energy, commencing in March 2000.     

Excimer laser annealing and chemical texturing of ZnO:Al sputtered at room temperature for photovoltaic applications

We demonstrate the effect of excimer (XeCl=308 nm) laser annealing on thin films of ZnO:Al deposited by RF sputtering at room temperature. The as-deposited films have good sheet resistance (<11 Ω/□) but poor transparency, and a subsequent chemical etching step using dilute HCl to texture the film surface results in a level of haze ineffective for light-trapping in thin film photovoltaic cells. Excimer laser annealing at the optimized fluence (single pulses of 0.5-0.7 J/cm²) improves the film transparency, particularly through a blue-shift in the band-gap, without significantly impacting the conductivity. More importantly, chemical etching of these laser annealed films results in textured films with controllable spectral distributions of haze. We demonstrate the enhanced optical properties (transmission and haze) after laser annealing and etching the ZnO:Al films through the fabrication of hydrogenated microcrystalline silicon pin solar cells, and show a significant improvement in the photocurrent density (up to 2.2 mA/cm²) for the optimally annealed substrates—particularly at wavelengths greater than 600 nm (up to 1.7 mA/cm²) where light-trapping is important.     

Modelling the light absorption in organic photovoltaic devices

Electromagnetic reflection, transmission and absorption properties are basically important for the optical characterization of multilayers used in optoelectronic and photovoltaic devices. They describe the interaction of incident light with the layers of the system. Depending on the thicknesses and optical constants of the individual layers, the interaction of a light source with a multilayer causes distinct distributions of the electric field and energy absorption density. Consequently the optical modelling of an organic bilayer photovoltaic device, in which the incident sunlight must be absorbed in a very narrow region near the active interface, has to take into account the influence of the optical parameters and the thicknesses of the device layers in order to gain optimal energy conversion. We focussed on the electrodynamic behavior of organic photovoltaic bilayer devices with varied layer thicknesses. We found a sensitive response of the maxima of the absorption density inside the solar cell to even fine changes in the thicknesses of the active layers. We also investigated the electrodynamic behavior of a photovoltaic device in dependence on the incident light wavelength. As a new and interesting result, our investigations showed a good correlation between measured photo current and calculated absorption density and no good correlation between measured photo current and calculated square of the electric field.     

Test facility in Port Said-Egypt for photovoltaic solar generators

In framework of an applied research project a test facility for evaluating the performance of photovoltaic (PV) solar generators has been implemented at the Faculty of Engineering in Port Said-Egypt. The goals of the project is to perform the different required tests on photovoltaic (PV) solar generators in order to verify the fulfillment of the international standard specifications and to verify the characteristics given by the manufacturer. This will be achieved determining the electrical, the thermal and the mechanical characteristics of the module. This test can be considered to be a preparation for Egyptian PV market helping for propagation and harmonisation of standards. The developed test facility is including the main tests of PV systems, e.g. the electrical output under normal operating conditions and the influence of different environmental factors.     

High-efficiency PERL and PERT silicon solar cells on FZ and MCZ substrates

High-efficiency PERL (passivated emitter, rear locally diffused) and PERT (passivated emitter, rear totally diffused) silicon solar cells have been fabricated on FZ and MCZ (magnetically confined Czochralski) substrates at the University of New South Wales. One of the PERL cells on FZ substrates demonstrated 24.7% efficiency at Sandia National Laboratories under the standard global AM1.5 spectrum (100 mW/cm²) at 25°C. Another PERT cell on a MCZ substrate, supplied by SEH, Japan, demonstrated 24.5% efficiency at Sandia under the same test conditions. Both these efficiencies are the highest ever reported for FZ and MCZ silicon cells, respectively. The cells made on MCZ substrates also showed stable cell performance.     

Short-term predictability of photovoltaic production over Italy

Photovoltaic (PV) power production increased drastically in Europe throughout the last years. Since about the 6% of electricity in Italy comes from PV, an accurate and reliable forecasting of production would be needed for an efficient management of the power grid. We investigate the possibility to forecast daily PV electricity production up to ten days without using on-site measurements of meteorological variables. Our study uses a PV production dataset of 65 Italian sites and it is divided in two parts: first, an assessment of the predictability of meteorological variables using weather forecasts; second, an analysis of predicting solar power production through data-driven modelling. We calibrate Support Vector Machine (SVM) models using available observations and then we apply the same models on the weather forecasts variables to predict daily PV power production. As expected, cloud cover variability strongly affects solar power production, we observe that while during summer the forecast error is under the 10% (slightly lower in south Italy), during winter it is abundantly above the 20%.     

A novel method to produce black silicon for solar cells

In the present study, the black silicon has been successfully produced by plasma immersion ion implantation (PIII). The microstructure and the reflectance of the black silicon have been investigated by field emission scanning electron microscope and spectrophotometer, respectively. Results show that the black silicon exhibits a needle-like structure with the average reflectance of 1.79%. The solar cell based on black silicon yields an efficiency of 15.68% with a fill factor (FF) of 0.783.