Technical Papers

Reduction of silicon wafer thickness without increasing the wafer’s strength can lead to a high fracture rate during subsequent handling and processing steps. The cracking of solar cells has become one of the major sources of solar module failure and rejection. Hence, it is important to evaluate the mechanical strength of silicon solar wafers and influencing factors. The purpose of this work is to understand the fracture behaviour of multicrystalline silicon wafers and to obtain information regarding the fracture of solar wafers and solar cells. The effects on silicon wafer strength of saw damage and of grain size, boundaries and triple junctions are investigated, while the effects of surface roughness and the damage layer removal process are also considered. Significant changes in fracture strength are found as a result of different silicon wafer crystallinity and surface roughness. Results indicate that fracture strength of a processed silicon wafer is mainly affected by the following factors: the saw-damage layer thickness, surface roughness, cracks/ defects at the edges and the number of grain boundaries – which all serve as possible crack initiation points. The effects of metallization paste type and firing conditions on the strength of solar cells are also considered, with findings indicating that the aluminium paste type and firing conditions influence the strength of solar cells.

This paper presents the Q-Cells research line (RL) as a core of the Reiner Lemoine Research Centre, including the technical set-up, the organization of the operation and current results of cell concepts processed in the RL on a regular basis. Trends of cell parameters for those processes are shown, and a focus is presented regarding the results of our high-efficiency cell concepts for multi- and monocyrstalline material processed in the RL with stabilized record efficiencies of 18.4% and 19.2%, respectively. In addition, we discuss the process flow and the results of a monitoring procedure that is used to check the rear-side passivation quality of the company’s equipment. Results of our current passivation stack show a surface recombination velocity of below Srear < 10cm/s, well suited to fabricating p-type Si solar cells with efficiencies above 20%.

When Stion started looking for sites to establish its first volume production plant, Mississippi was not even on its radar. After vetting some “100 different opportunities, state and local flavors and locations,” the San Jose-based thin-film PV module company had “narrowed the list down to a half-dozen or so pretty quickly,” including Texas, Virginia, Michigan, and California, according to CEO Chet Farris.

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.

One of the most important ways in which inorganic thin-film photovoltaics (TFPV) and organic photovoltaics (OPV) can distinguish themselves from more conventional crystalline silicon photovoltaics (c-Si PV) in the marketplace is through the commercialization of flexible photovoltaic products using those technologies. But flexible photovoltaics brings with it some challenges of its own in terms of excluding air and moisture from the cells; challenges that translate into opportunities for suppliers of advanced encapsulation materials and systems as well as for TFPV and OPV firms.

This article provides an overview of the typical waste water treatment methods for crystalline silicon solar cell production. Firstly, a short description is provided of the main process steps of photovoltaic production and the types of waste water generated during these steps. Secondly, the typical waste water treatment methods of hydrogen fluoride (HF) precipitation and neutralization are presented. Furthermore, some options for the reuse of rinse water are discussed and several guidelines for the design of waste water treatment systems are given. Finally, the relative environmental impact of the waste water treatment compared to the emissions of the whole fab is presented using the life-cycle assessment (LCA) methodology.

This paper discusses the wire sawing process and its impact on the wafer surface and subsurface. Surface damage is found to be the main determinant in wafer stability, while an outline of the sawing parameters that have a strong influence on the surface and subsurface damage is presented. The results indicate how it is possible to decrease the breakage rate of wafers and improve the homogeneity (e.g. TTV) of wafer surfaces. A further goal in the development of the wire sawing process is to successfully reduce material consumption. This can be achieved by sawing thinner wafers with thinner wires, which leads to a reduction of the kerf loss per produced silicon surface. The second option is to increase the material yield by decreasing the wafer breakage. It will be shown that silicon wafers with less and shorter cracks and smoother surfaces will give a higher yield, while proceeding to discuss some of the important factors that affect the microcrack formation.

Recent industry analysis from NanoMarkets has suggested that although current business cases for PV are running out of steam, the building-integrated PV (BIPV) sector may be able to revive PV’s fortunes. The arrival of ‘true’ BIPV – not just flush-mounted BIPV panels, but PV-enabled glass, tiles, siding, etc. – renders possible new business cases that would otherwise simply not be an option with conventional PV. This paper puts forth a business analysis of the BIPV industry, providing case studies and data on the burgeoning sector.

With more than 80% of PV module demand being satisfied by crystalline-based modules, the health of the silicon and wafer supply chain is of vital importance to the overall PV industry. This paper reviews the overall materials value chain from the manufacture of PV silicon to the wafer, prepared for manufacture of the cell. A glimpse is provided of the various market dynamics that exist in the supply chain, as well as the technology trends that influence or threaten the supply of wafers. Although the manufacturing routes are mature and well established, we also take a look at the possibility of novel and disruptive technologies altering the overall supply landscape.

Germany and Italy are forecasted to drive solar demand to new highs in 2011, with rumours of installations up to 22GW on the cards for this year. The German and Italian markets, scheduled to peak in 2011 and 2012, respectively, face a potential problem in terms of where to sell their modules if these two countries cannot accommodate 10GW of installations per year. The emerging markets can solve part of this challenge and will deliver new opportunities to the solar industry. Some Asian, European and Middle Eastern regions will require up to of 6GW of solar-generated electricity, while the Americas, Africa and Australia are each projected to install approximately 1GW in 2014. This paper takes a look at the development of these emerging markets and provides a projection of likely installation figures up to 2015.