PVI Issue

Photovoltaics International Volume 10

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The tenth edition of Photovoltaics International was published in November 2010. In this edition, Q-Cells SE demonstrates the benefits of laser marking, Fraunhofer IST presents TCO deposition techniques in Thin Films, and we take an in-depth look at the benefits of using selective emitters on an industrial scale with Neo Solar Power.

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In this issue...

PVI Paper
Photovoltaics International Papers
One of the busiest of the couple-dozen solar manufacturing factory floors I’ve seen this year belonged to ECD Uni-Solar, at its Auburn Hills 2 (AH2) facility just up the road from the Palace where the NBA’s Detroit Pistons play hoops. When I toured the plant in late July, the three production areas – cell deposition, cell finishing, and module stringing/lamination/final assembly – were humming, as the 1.5-milelong rolls of flexible stainless-steel starting material were transformed into triplejunction amorphous-silicon thin-film PV laminates. The company’s latest quarterly results confirm those observations at the factory, as production output grew some 58% over the previous period – from 21.2MW to 33.6MW – pushing capacity utilization to about 90%.
PVI Paper
Materials, Photovoltaics International Papers
The minority carrier lifetime is a key parameter for the performance of solar cells as it characterizes the electrical quality of the semiconductor material. Consequently, accurate and reliable methods to determine the minority carrier lifetime are of enormous interest for both practical process control and the evaluation of the potential and limitations of a specific cell concept. Due to its importance, many different lifetime measurement techniques have been developed and used over the past few decades. This paper aims to present and discuss the most common measurement methods on the one hand, while attempting to shed light on some recent developments on the other. The determination of the minority carrier lifetime of crystalline silicon thin-film (cSiTF) material is illustrated as an example of interest for those who are already familiar with standard lifetime characterization.
PVI Paper
Photovoltaics International Papers, Thin Film
Highly conductive transparent films are of significant interest in the field of thin-film photovoltaics. The solar cell type defines the necessary properties of the TCO used, as, besides the obvious qualities of transparency and conductivity, stability and morphology are important. The most significant properties of these aspects for front contacts in amorphous/microcrystalline silicon tandem, CIGS and CdTe solar cells are presented in this paper. Commonly used deposition techniques like CVD and sputter technology are described herein, focusing on particular techniques like SnO2:F and ZnO:B (CVD) and ZnO:Al (sputtering). New developments of deposition methods are also discussed.
PVI Paper
Photovoltaics International Papers, Thin Film
Magnetron-sputtered ZnO:Al is often used as a front contact in thin film silicon solar cells due to its transparent conductive oxide (TCO) properties that allow texturization by chemical etch processes to introduce light trapping. The transparency, conductivity, and surface texture after etching depend strongly on the sputtering conditions. Consequently, the typical preparation method is to find the right balance in TCO properties and light scattering, leading to a very narrow sputtering parameter window. It is preferable to separate the electro optical optimization from that of texturization to allow for a larger process window and improve ZnO:Al film properties further. This paper presents some methods of controlling the surface features using various mixtures of two step etching processes in aqueous solutions of HF and HCl. Results include methods for controlling the density of craters, texturizing compact ZnO:Al films, and fabricating novel modulated surfaces with more than one characteristic feature size. The two step etch process enables the creation of good surface textures even on high rate material that, via state of the art HCl etching, tend to lead to poor solar cell performance.
PVI Paper
Photovoltaics International Papers, Thin Film
The three most viable thin-film photovoltaic technologies – cadmium telluride (CdTe), copper-indium gallium (di)selenide (CIGS), and amorphous silicon (a-Si) – continue to mature and grow technologically and in market stature. But apart from the dominance shown by CdTe leader First Solar, the rest of the TFPV manufacturers have had a fairly difficult time making significant commercial inroads as the price of mainstream crystalline-silicon modules plummeted over the past couple of years. Other factors delaying the long-predicted age of thin film include bankability challenges and difficulties in reducing production and system costs. Yet entrants in all three thin-film categories have reason for optimism, as they push toward a competitive market position. This paper provides an overview of the current status of the thin-film PV sector and its players, offering insights into why certain companies might emerge successfully in the years ahead.
PVI Paper
Photovoltaics International Papers, PV Modules
This paper presents fluorescence detection as a new tool for the investigation of the degradation of EVA. The superior sensitivity of the set-up contained herein allows an early assessment of the changes of the EVA after only 20 hours of damp-heat exposure. A newly developed scanning system allows the spatially resolved inspection of entire PV modules. Degradation of the encapsulants was detectable after two years’ outdoor exposure, as was the effect of cracks in c-Si cells, which coincide well with cracks made visible by electroluminescence.
PVI Paper
Photovoltaics International Papers, PV Modules
This paper, the fourth in a series covering cost modelling studies for photovoltaics [1–3], examines a new approach to module assembly based on the concept of ‘supersized’ 1kW PV modules. Using supersized modules (1.6m × 3.8m) and integrated microinverters, this novel approach has the estimated potential to save utility solar installations nearly $0.50/Watt. The paper will conclude with a detailed cost and resource case study comparing two 40MW module lines, one employing ‘solar breeder’ technology and the other producing conventional-sized modules.
PVI Paper
Photovoltaics International Papers, PV Modules
Solar enterprises will each be faced with the occasional surplus or lack of solar modules in their lifetimes. In these instances, it is useful to adjust these stock levels at short notice, thus creating a spot market. Spot markets serve the short-term trade of different products, where the seller is able to permanently or temporarily offset surplus, while buyers are able to access attractive offers on surplus stocks and supplement existing supply arrangements as a last resort.
PVI Paper
Photovoltaics International Papers, Power Generation
PV industry module and component manufacturers have brought down costs significantly over the last four years. This trend is clearly evident as most publicly traded companies continue to grow revenue despite falling module and component prices. However, it is far less clear how downstream system integrators are handling the drop in system prices and contributing to value creation. System prices are generally higher in the U.S. than in Europe despite lower module prices in the U.S. This disparity often raises questions on the part of European PV professionals where these costs come from, and secondly, what have U.S. system integrators done to reduce costs. This article is the second of a two-part series shedding light on how U.S. integrators contribute to a decreasing installed-PV-system cost roadmap by championing value creation in the downstream segment. Focusing on the residential market segment, Part I delved into activity cost savings through innovation in engineering and construction [1]. Part II illustrates how changes in marketing and sales, rebates, interconnection, supply chain management and customer support have evolved considerably over the last several years to result in reduced costs.
PVI Paper
Materials, Photovoltaics International Papers
Despite the financial crisis and present credit crunch, photovoltaic materials markets experienced only a temporary slide in demand in 2009, with the overall outlook remaining optimistic. This paper presents a strategic analysis review for the materials used in photovoltaic modules, essentially materials for encapsulant, frontsheet, backsheet and anti-reflection coatings. Rising concerns about the need to reduce CO2 emissions and increase the use of renewable energy sources worldwide will stimulate the global photovoltaic market. Feed-in tariffs and politically backed targets boosting renewable energy use will provide further impetus to the photovoltaic market. This, in turn, will have a positive ripple effect on the demand for photovoltaic materials; however, depending on the market share for technology used, i.e. crystalline or thin film for PV energy, the market for materials will be influenced, in addition to advantages and disadvantages of these materials that will influence their market share. With rising awareness about green trends, the future will lie in technologies that offer enhanced energy-efficient solutions at a low cost. Manufacturers who offer products with optimum performance while remaining price-orientated will be poised to gain substantial market share.
PVI Paper
Materials, Photovoltaics International Papers
The next generation of industrial silicon solar cells aims at efficiencies of 20% and above. To achieve this goal using ever-thinner silicon wafers, a highly effective surface passivation of the cell, front and rear, is required. In the past, finding a suitable dielectric layer providing a high-quality rear passivation has been a major challenge. Aluminium oxide (Al2O3) grown by atomic layer deposition (ALD) has only recently turned out to be a nearly perfect candidate for such a dielectric. However, conventional ALD is limited to deposition rates well below 2nm/min, which is incompatible with industrial solar cell production. This paper assesses the passivation quality provided by three different industrially relevant techniques for the deposition of Al2O3 layers, namely high-rate spatial ALD, plasma-enhanced chemical vapour deposition (PECVD) and reactive sputtering.
PVI Paper
Market Watch, Photovoltaics International Papers
The U.S. solar PV market is suffering not from a lack of demand or high prices, but rather from an inconsistent labyrinth of rules and regulations which complicate and prolong uptake. There is significant pent-up demand in the U.S. among developers and especially manufacturers; there is not, however, a commensurate regulatory framework that will enable and encourage this demand to be realized. The U.S. political landscape is deeply divided, and policies that would directly or indirectly effect solar demand are no different from any other in this regard.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
A major challenge for the solar industry over the next few years is the reduction of production costs on the road to grid parity. Capacity must be increased in order to leverage scaling effects, production and cell efficiency must also be enhanced, and the industry must focus on intensified process optimization and quality control. Laser marking can make a key contribution to fulfilling these requirements. As hard physical coding, laser marking is applied to the raw wafer at the start of the manufacturing process, making each solar cell traceable along the entire value chain and over its whole lifetime. This paper presents Q-Cells’ laser-supported process for coding each individual solar cell (European patent pending), which will require transition work at the laboratory stage before the company’s innovation is ready for mass production.
PVI Paper
Fab & Facilities, Photovoltaics International Papers
The recent 30% decline in module market prices is the most telling sign of a need for continuous reductions in PV production costs. With this in mind, the cost efficiency of production processes is, next to stable product quality, a vital objective in the planning of production facilities. In this paper, the lessons learned in the area of cost of ownership (COO) forecasting methodologies will be analyzed and evaluated for their potential application to investment decisions in the PV industry. This paper will analyze the cost structure of the PV industry with the aim of underlining the importance of a systematic cost-of-ownership approach.
PVI Paper
Cell Processing, Photovoltaics International Papers
Laser grooved buried contact (LGBC) solar cell technology is proving to be an attractive method of producing solar cells that are designed to operate at one sun and at concentration. Such technology is commercially available at Narec for applications at up to 100 suns. Although LGBC cells can have a higher efficiency at one sun when compared with standard non-selective emitter screen-printed solar cells, a more complex manufacturing process is required for these cells. This paper outlines the approach taken under the FP6 EU funded project “Lab2Line”, in which screen-printing and LGBC solar cell processing techniques are hybridized in order to produce lower cost, high efficiency solar cells.
PVI Paper
Cell Processing, Photovoltaics International Papers
The workhorse of the photovoltaic industry, crystalline-silicon solar cells, continues to have additional headroom for conversion efficiency improvement as well as decreased production costs. As some companies have already demonstrated, clear pathways exist to bring about the achievement of >20%-efficient monocrystalline cells through the use of existing and novel production techniques. A newcomer to the solar cell and module sector, Suniva, has rapidly become a volume manufacturer using innovations originally developed at the University Center of Excellence in Photovoltaics (UCEP) at the Georgia Institute of Technology. This paper discusses the company’s first- and second-generation production technologies, including the implementation of ion implantation as a high-volume process, as well as details of cell-making approaches in the development stage.
PVI Paper
Cell Processing, Photovoltaics International Papers
A selective emitter is a doping layer that is heavily doped beneath the electrode and lightly doped in between the electrode grids. One of the disadvantages of conventional selective-emitter techniques is the need for a high phosphorus surface concentration to obtain low contact resistance and limit the shunts in the emitter. Effective emitter passivation below the contact is difficult because of the use of emitters with low sheet resistances and high doping concentrations. In this study, the selective emitter in the optimized light/light sheet-resistance combination was formed to reduce recombination under the metal contact. The fabrication of optimized light/light doped emitters was performed using a single-step diffusion process. Besides the benefit of low surface recombination for light/light combination, this approach also removes the need for a very precise alignment between the opened emitter pattern and the front screen-printed silver fingers. This work illustrates the achievement of an efficiency improvement of more than 0.4% absolute in large-scale production for selective emitter solar cells.
PVI Paper
Cell Processing, Photovoltaics International Papers
A hydrogenated amorphous Si (a-Si:H) film, combined with a silicon nitride (SiNx:H) capping layer and a post-deposition anneal, can hugely enhance the surface passivation on crystalline silicon wafers. In this work, the influence of various deposition temperatures of a-Si:H films on the thermal stability of a-Si:H/SiNx:H stacks and a possible mechanism are discussed. Both minority carrier lifetime measurement and grazing-angle XRD were employed to study the thermal stability of a-Si:H/SiNx:H stacks, and the results are interpreted in terms of dihydrides concentration and epitaxial crystallization. With an appropriate thermal treatment, the a-Si:H film deposited at 130°C and capped by SiNx:H showed better passivation performance than 200°C-deposited a-Si:H/SiNx:H stacks, but under an excessive thermal budget the former showed more severe degradation of carrier lifetime. The more dihydride-rich composition within 130°C-deposited a-Si:H/SiNx:H stacks could be regarded as providing more effective intermediates for hydrogen interchanges, but on the other hand, it is also more susceptible to epitaxial crystallization.
PVI Paper
Photovoltaics International Papers, Power Generation
As it makes its way towards a non-subsidised market, the photovoltaic sector has to deal with decreasing margins. To ensure investment goals are met in spite of this, it is imperative that PV power plants generate optimal yields. Comprehensive quality assurance for PV power plants covers all phases of the completion process from the planning to system operation. This article explains the extent of standard quality assurance measures that include yield assessments, module measurements, system testing and yield monitoring. It outlines the potential of linking these quality assurance measures and stresses the importance of the measures themselves being of high quality. Up-to-date scientific findings from Fraunhofer ISE are presented in order to further optimise quality assurance measures.

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