Astrid Gutjahr

Ribbon Growth on Substrate and Molded Wafer-Two Low Cost Silicon Ribbon Materials for PV

This paper focuses on two very promising silicon ribbon materials currently produced for research: ribbon growth on substrate (RGS) by ECN solar energy and molded wafer (MW) by GE Energy. Both materials are investigated in terms of solar cell processing and characterisation. First cell results of large area 10times10 cm2 RGS cells are presented as well as results from 5times5 cm2 cells processed from 8times12 cm2 RGS and 12.5times12.5 cm2 MW wafers

Screen-printed ribbon growth on substrate solar cells approaching 12% efficiency

Ribbon growth on substrate (RGS) solar cells have been processed at the University of Konstanz using an adapted industrial-type fire-through SiN process. An efficiency of 12.3% has been reached on a 5/spl times/5 cm/sup 2/ cell. This is the highest efficiency obtained on this very promising and cost-effective material using an industrial-type cell process. An important factor for the increase in efficiency was the reduced oxygen concentration of almost an order of magnitude in the current RGS wafer material compared to former RGS material. Enhanced J/sub sc/, V/sub oc/ and L/sub eff/ values in the range of 100 /spl mu/m as well as lifetimes above 4 /spl mu/s demonstrate the potential of the new low oxygen RGS material. Efficiencies well above 13% should be possible, provided a surface texture is applied and shunting mechanism can be avoided.

Impact of oxygen on carbon precipitation in polycrystalline ribbon silicon

This article reports experimental evidence for the effect of oxygen on carbon precipitation in polycrystalline ribbon silicon. Four sets of wafers subject to various heat treatments have been examined by infrared spectroscopy. It is found that carbon precipitation in an oxygen-containing wafer consists of two distinct steps, namely, an initial rapid oxygen–carbon coprecipitation in the very first hour annealing, followed by slow precipitation during subsequent prolonged annealing. A high oxygen content enhances carbon precipitation throughout the two steps. It is shown that the formation of interstitial carbon in the presence of excess silicon self-interstitials generated during oxygen precipitation plays an important role in increasing the carbon precipitation rate in the first hour annealing. Because of the absence of interstitial injection during the following slow precipitation process, the enhancement effect of oxygen can only arise from an increase in precipitation sites. It is proposed that the oxy...

Compatibility of the RGS silicon wafer with industrial type solar cell processing

The ribbon-growth-on-substrate (RGS) silicon wafer technology is a unique casting technology for the next generation of silicon wafer manufacturing for photovoltaic application. Compared to todays cut wafer technology, the silicon yield is increased from about 40% to more than 90% due to the direct casting. This in combination with the high production volume per machine and year makes RGS wafers a promising technology for the next step towards cost effective solar electricity. However, for a successful implementation of this technology in the market, not only the wafer manufacturing process but also the compatibility of the RGS wafers with todays solar cell lines has to be demonstrated. This paper presents an overview on the lessons learned in the last 7 years of solar cell processing of RGS wafers manufactured with the laboratory equipment at ECN.