Application of ITO/Al reflectors for increasing the efficiency of single-crystal silicon solar cells

It is shown that an increase in the efficiency and manufacturability of single-junction single-crystal silicon photoelectric converters of solar energy requires the use of a back-surface reflector based on conductive transparent indium-tin oxide (ITO) 0.25–2 μm thick. To increase the efficiency and reduce the sensitivity to the angle of light incidence on the photoreceiving surface of multijunction photoelectric converters with vertical diode cells based on single-crystal silicon, ITO/Al reflectors with an ITO layer >1 μm thick along vertical boundaries of diode cells should be fabricated. The experimental study of multijunction photoelectric converters with ITO/Al reflectors at diode cell boundaries shows the necessity of modernizing the used technology of ITO layers to achieve their theoretically calculated thickness.     

Simulation and implementation of a porous silicon reflector for epitaxial silicon solar cells

One of the main challenges in the ongoing development of thin film crystalline silicon solar cells on a supporting silicon substrate is the implementation of a long‐wavelength reflector at the interface between the epitaxial layer and the substrate. IMEC has developed such a reflector based on electrochemical anodization of silicon to create a multi‐layer porous silicon stack with alternating high and low porosity layers. This innovation results in a 1–2% absolute increase in efficiency for screenprinted epitaxial cells with a record of 13·8%. To reach a better understanding of the reflector and to aid in its continued optimization, several extensive optical simulations have been performed using an in‐house‐developed optical software programme. This software is written as a Microsoft Excel workbook to make use of its user‐friendliness and modular structure. It can handle up to 15 individual dielectric layers and is used to determine the influence of the number and the sequence of the layers on the internal reflection. A sensitivity analysis is also presented. A study of the angle at which the light strikes the reflector shows separate regions in the physical working of the reflector which include a region where the Bragg effect is dominant as well as a region where total internal reflection plays the largest role. The existence of these regions is proved using reflection measurements. Based on these findings, an estimate is made for the achievable current gain with an ideal reflector and the potential of epitaxial silicon solar cells is determined. Copyright © 2008 John Wiley & Sons, Ltd.     

Buried-contact silicon solar cells

Recent technological and commercial developments for the buried-contact solar cell (BCSC) are reviwed. Four of the world's largest manufacturers have entered into manufacturing agreements, with a number of these taking advantage of the high-efficiency capabilities of the large-area BCSCs to produce cells for solar cars in the 1990 and 1993 World Solar Challenges and in the solar car race across the USA in 1993. Despite the efficiencies and commercial interest acheived by the conventional structure for the BCSC, a number of areas for improvement remain. In particular, the rear aluminium-alloyed region limits the cell performance, and dislocation generation resulting from stresses at the silicon/silicon dioxide interface can also play a significant role in reducing efficiencies. Through the use of a photolithographically defined rear metal contact, efficiencies in excess of 21% and open-circuit voltages as high as 693 mV for the hybrid BCSC have been demonstrated. the effect of the heavily diffused region beneath the metal contacts in the grooves is studied and its implications for the new generation of BCSCs with grooves on front and rear surfaces are considered. the economic and technological merits of a range of groove formation approaches are discussed, with a low-cost, high-throughput ganged dicing wheel saw with 35 wheels showing most promise.     

Amorphous silicon solar cells

Amorphous silicon solar cells have been fabricated in several different structures: heterojunctions, p-i-n junctions, and Schottky barrier devices. The procedures used in constructing the various solar cells are discussed, and their photovoltaic properties are compared. At present, the highest conversion efficiency (5.5 percent) has been obtained with a Schottky barrier cell, and this structure appears to offer the best promise of approaching the estimated efficiency limit of ∼ 15 percent.     

The monolithic multicell: a tool for testing material components in dye‐sensitized solar cells

A multicell is presented as a tool for testing material components in encapsulated dye‐sensitized solar cells. The multicell is based on a four‐layer monolithic cell structure and an industrial process technology. Each multicell plate includes 24 individual well‐encapsulated cells. A sulfur lamp corrected to the solar spectrum has been used to characterize the cells. Efficiencies up to 6·8% at a light‐intensity of 1000 W/m^su2 (up to 7·5% at 250 W/m²) have been obtained with an electrolyte solution based on γ‐butyrolactone. Additionally, a promising long‐term stability at cell efficiencies close to 5% at 1000 W/m² has been obtained with an electrolyte based on glutaronitrile. The reproducibility of the cell performance before and after exposure to accelerated testing has been high. This means that the multicell can be used as an efficient tool for comparative performance and stability tests. Copyright © 2006 John Wiley & Sons, Ltd.     

Point-contact silicon solar cells

A new type of silicon photovoltaic cell designed for high-concentration applications is presented. The device is called the point-contact-cell and shows potential for achieving energy conversion efficiencies in the neighborhood of 28 percent at the design operating point of 500× geometric concentration and 60°C cell temperature. This cell has alternating n and p regions that form a polkadot array on the bottom surface. A two-layermetallization on the bottom provides contact. Initial experimental results have yielded a cell with 20-percent efficiency at a concentration of 88.     

Transverse probe optical lifetime measurement as a tool for in-line characterization of the fabrication process of a silicon solar cell

In this paper an all-optical measurement procedure for the characterization of minority carrier recombination lifetime and surface recombination velocity is presented as a reliable tool to monitor the fabrication process of a standard crystalline silicon solar cell. In the methodology presented here, there are no stringent requirements concerning the state of wafer surface. The IMEC (Interuniversity Microelectronics Centre, Leuven, Belgium) fabrication process is taken as an example of the capability of this method to monitor the whole process from the silicon wafer to the finished cell. It is shown that the cell process does not degrade the bulk recombination lifetime and that the effect of the external surfaces is effectively screened.     

Electrochemically passivated contacts for silicon solar cells

Electrochemically passivated Ti(Pd)Ag contacts for Si solar cells have been developed. The passivation is accomplished by shifting the electrochemical exchange potential of the Ti/Ag couple into positive direction by the addition of a layer of Pd between the Ti and the Ag layers. The new contacts do not degrade during humidity stress tests. They withstand temperature cycling from -- 196°C to +150°C, can be subjected to high temperatures, and are compatible with solderless interconnection schemes.     

Double-layered silicon nitride antireflection coatings for multicrystalline silicon solar cells

Silicon nitride coating possesses both optical antireflection and electrical passivation effects for crystalline silicon solar cells. In this work, we employed a double-layered silicon nitride coating consisting of a top layer with a lower refractive index and a bottom layer (contacting the silicon wafer) with a higher refractive index for multicrystalline silicon solar cells. Double-layered silicon nitride coating provides a lower optical reflection and better surface passivation than those of single-layered silicon nitride. Details for optimizing the double-layered silicon nitride coating are presented. In order to get statistical conclusions, we fabricated a large number of multicrystalline silicon solar cells using the production line for both the double-layered and single-layered cell types. It was statistically demonstrated that the double-layered silicon nitride coating provided a consistent enhancement in the photovoltaic performance of multicrystalline silicon solar cells over those of the single-layered silicon nitride coating.     

用位误差率测试仪作为解决问题的工具

具有误差位置分析的位误差率测试仪已经长期应用于研发环境,以改善和评价数据存储和通讯领域中各种各样的系统和部件的性能。随着对位误差率是数据完整性中最明确的测量指标的日益认可,这些设备在通讯系统和部件的生产测试环境中得到了更广泛的应用。 一种用于评测高速多路复用器和信号分离器的独立的并联BER测试仪使这种倾向得到了加强,而且经常可     

Thin monocrystalline silicon solar cells

One of the most effective approaches for a cost reduction of crystalline silicon solar cells is the better utilization of the crystals by cutting thinner wafers. However, such thin silicon wafers must have sufficient mechanical strength to maintain a high mechanical yield in cell and module manufacturing. The electrical performance of thin cells drops strongly with decreasing cell thickness if solar cell manufacturing technologies without a backside passivation or a back-surface-field (BSF) are applied. However, with the application of a BSF, stable efficiencies of over 17%, even with decreasing cell thickness, have been reached. Thin solar cells show lower photodegradation, as is normally observed for Cz-silicon cells with today's standard thickness (about 300 μm) because of a higher ratio of the diffusion length compared to the cell thickness. Cells of about 100-150 μm thickness fabricated with the production Cz-silicon show almost no photodegradation. Furthermore, thin boron BSF cells have a pronounced efficiency response under backside illumination. The backside efficiency increases with decreasing cell thickness and reaches 60% of the frontside cell efficiency for 150 μm solar cells and also for solar modules assembled of 36 cells of a thickness of 150 μm. Assuming, for example, a rearside illumination of 150 W/m², this results in an increased module power output of about 10% relatively     

High-efficiency ion-implanted silicon solar cells

The development of solar cells with AM1 coversion efficiency of 18 percent is reported. The cells comprise an n⁺-p-p⁺structure fabricated from float zone silicon having resistivity of 0.3 Ω . cm. The n⁺and p⁺regions are formed by low energy ion implantation and thermal annealing. An important feature of cell fabrication is the growth of SiO2passivation for reduction of surface recombination velocity. Details of both cell fabrication and testing are reported.     

Impurities in silicon solar cells

The effects of various metallic impurities, both singly and in combinations, on the performance of silicon solar cells have been studied. Czochralski crystals were grown with controlled additions of secondary impurities. The primary dopants were boron and phosphorus while the secondaires were: A1, B, C, Ca, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, P, Pd, Ta, Ti, V, W, Zn, and Zr. Impurity concentrations ranged from 10¹⁰to 10¹⁷/cm³. Solar cells were made using a conventional diffusion process and were characterized by computer reduction ofI-Vdata. The collected data indicated that impurity-induced performance loss was primarily due to reduction of the base diffusion length. Based on this observation, an analytic model was developed which predicts cell performance as a function of the secondary impurity concentrations. The calculated performance parameters are in good agreement with measured values except for Cu, Ni, and Fe, which at higher concentrations, degrade the cell substantially by means of junction mechanisms. This behavior can be distinguished from base diffusion length effects by careful analysis of theI-Vdata. The effects of impurities in n-base and p-base devices differ in degree but submit to the same modeling analysis. A comparison of calculated and measured performance for multiple impurities indicates a limited interaction between impurities, e.g., copper appears to improve titanium-doped cells.     

Novel porous silicon backside light reflector for thin silicon solar cells

High efficiencies of thin crystalline Si solar cells grown on highly doped substrates have been reported. We propose porous Si layers located near the interface of the active layer and the substrate to introduce an optical confinement into these cells. We report on the experimental proof of the principle for this novel type of back-surface reflector. Spectral reflectance measurements agree well with computer simulations. On the basis of this agreement, we calculate the enhancement of short-circuit current densities due to porous reflectors for textured and non-textured cells. These simulations are of particular relevance for multicrystalline Si cells on foreign substrates and for space cells. Copyright © 1998 John Wiley & Sons, Ltd.     

Polycrystalline silicon solar cells on metallurgical silicon substrates

The use of a polycrystalline silicon p-n junction structure deposited on low-cost substrates is a promising approach for the fabrication of low-cost solar cells. Metallurgical-grade silicon, with a purity of about 98% and a cost of about $1/kg, was cast into plates in a boron nitride container and used as substrates for the deposition of solar cell structures. The substrates were polycrystalline with millimeter size crystallites. Solar cells of the configurations n>⁺-silicon/p-silicon/metallurgical silicon and n⁺-silicon/p⁺-silicon/metallurgical silicon were prepared by the thermal decomposition of silane and the thermal reduction of trichlorosilane containing appropriate dopants. The AMO efficiencies of n⁺-silicon/p-silicon/metallurgical silicon solar cells were up to 2.8% (with no anti-reflection coatings) and were limited by the grain boundaries in the p-layer. The grain boundary effects were reduced by increasing the dopant concentration in the p-layer, and AMO efficiencies of about 3.5% were obtained from n⁺-silicon/p⁺-silicon/metallurgi silicon solar cells.