Technical Papers

Apart from some obstacles and bureaucratic hindrances, the Italian PV market has recently joined the upper echelons of the solar industry. Along with small and medium-sized systems, the commercial and large-scale segment in particular has a great deal of promise. Even though the local industry is still trying to block the domestic market from international competitors, increasing numbers of foreign investors are entering the market. In this close-up of the Italian PV market, the country’s participation in the solar energy industry is reviewed and a projection to 2010 is given, with particular emphasis on the country’s potential to be a major player in the large-scale installation sector.

Anyone familiar with the PV industry can attest to the remarkably accelerated pace of innovation aimed towards generating solar power more cost effectively relative to conventional means of producing electricity. Many of high-technology’s best minds are bringing expertise in materials, manufacturing process, and electronics to tackle the challenge. The resultant gains in cost effective manufacturing, silicon availability and greater irradiance conversion efficiency will make continuous and sustainable impact to cost per kW generated akin to the predicable improvements in transistors per mm2 which has fuelled the semiconductor industry for the past 25 years (although we are not yet so bold as to devise the PV version on Moore’s Law). As less than 0.01% of electricity generated comes from PV installations [1], demand will materialize and the need for public subsidies will decline as the economics improve. This paper will investigate the steps required to make every solar project a “perfect” project by putting forth parameters for evaluating solutions for the problem areas.

The use of perfluorinated gases such as NF3, CF4 or SF6 for PECVD (plasma enhanced chemical vapor deposition) chamber cleaning has a much higher impact on global warming than does the use of onsite-generated F2. This holds true even when supposing that in the future much more effort is paid for the correct abatement and a leak-free supply and take-back chain. This paper will discuss the steps available to the PV industry for control and reduction of carbon emissions in the chamber cleaning process.

Although the entire solar manufacturing industry, from raw materials to finished modules, has enjoyed strong double-digit growth rates over the past several years, few sectors have soared like the amorphous-silicon thin-film photovoltaic equipment space. Much of this prodigious multibillion-dollar booking activity can be attributed to the acceptance of the turnkey production packages offered by the likes of Applied Materials, Oerlikon and Ulvac. These suppliers’ plug-and-play, standard toolset solutions are attractive to companies seeking to get into the TFPV module business on a fast track and then scale up their capacities in multimegawatt chunks to achieve grid-competitive cost-per-manufactured-watt metrics.

With the thin-film silicon industry facing the problems of high-quality material deposition at high rates and narrowing deposition process windows, the “no-drift regime” is an important part of this development. In the case of the plasma-enhanced chemical vapor deposition (PECVD) of thin silicon films, the inconstancy of the concentration of silicon-containing particles (SCP) in the plasma leads to changes in deposition conditions, causing a deterioration of film properties, and, therefore, decreasing the performance of the solar cells. During the last few decades, evidence about the process instabilities has been accumulated in different laboratories. In this study, Fourier transform infrared absorption spectroscopy (FTIR), optical emission spectroscopy (OES), self-bias voltage and plasma impedance controls were applied as in-situ process diagnostics during the deposition of amorphous and microcrystalline silicon thin-films. Results of the study were then discussed.

The etching technology currently used in the solar industry is mostly based on wet chemical processing. Plasmaenhanced dry chemical etching at atmospheric pressure is an alternative to the existing technology, especially when combined with similar process technologies, for example plasma-enhanced deposition techniques at atmospheric pressure, to provide a continuous in-line processing of crystalline silicon solar cells. This paper presents the use of plasma chemical etching using Fourier Transform infrared (FT-IR) spectroscopy to monitor different silicon wafer processing steps as an alternative to the widely used wet chemical processing approach.

The Semiconductor Equipment and Materials International (SEMI) International Standards Program has a proven track record of more than 35 years of facilitating standards for high-tech industries, and aims to apply its experience to the emerging PV industry. Unlike other pre-established industries, where standard activities are mainly initiated by mature companies with clear requirements to standards, the PV industry, with its huge number of newly founded companies, is currently focused on ramping up their production lines and stabilizing their production processes. By structuring and utilizing standards requirements, it is possible to focus recourses to the most valuable standards in this critical phase of the fast-growing PV industry. SEMI intends to achieve these goals by proving recommendations for new standards activities, linking experts together to accomplish the deliverables, and speed up the process of standards deployment.

Inline processing, one of the fastest-growing production processes for crystalline silicon solar cells, uses continuously operated belt furnaces to achieve higher overall throughput compared with traditional batch processing. A second, major advantage of inline processing is improved manufacturing yields through reduced breakage of today’s thinner, increasingly delicate wafers. This is accomplished by eliminating several handling steps unique to batch processing techniques. This paper describes the influence of ECN-Clean, as developed by Mallinckrodt Baker and ECN in 2006, whose application increases the efficiency of solar cells produced using inline processing by approximately 0.3 percent absolute, compared with standard inline processing.

Investments in large photovoltaic factories can lead to high capital expenditure. To achieve a fast return on investment, it is essential to ensure a high utilization of process equipment. Optimization of photovoltaic factory performance requires a fundamental understanding of the processes as well as of the material flow and manufacturing equipment. Fraunhofer IPA has developed an approach to gather and analyze the factory data in order to detect and understand the logistic influencing factors. With this factory data, the performance of material flow systems and production equipments can be evaluated, leading to detection and elimination of inefficiencies in the manufacturing lines. The methods of acquiring and analyzing factory performance data as outlined in this article mainly focus on thin-film manufacturing lines, but are also applicable to crystalline technologies.

A new wafer technology, named CDS (Crystallization on Dipped Substrate), is under development and has been found to be effective in the reduction of wafer cost and silicon feedstock. CDS technology was applied to 156mm x 156mm-sized wafers, obtained via the throughput of 1825cm2/min, and the resulting cell efficiency of 14.8% was confirmed. This paper outlines the principle behind the technology and outlines the procedure.