Wolfgang Appenzeller

Microcrystalline silicon for large area thin film solar cells

Abstract We present a comprehensive study of microcrystalline silicon (μc-Si:H) solar cells prepared by plasma-enhanced chemical vapour deposition (PECVD) at 13.56 MHz excitation frequency. In the first step the cell development was performed in a small area PECVD reactor showing the relationship between the deposition process parameters and the resulting solar cell performance. Focus was on the influence of deposition pressure, electrode distance and the application of a pulsed plasma on high rate deposition of solar cells. Subsequent up-scaling to a substrate area of 30×30 cm 2 confirmed the suitability of the process for large area reactors. The influence of i-layer deposition parameters on solar cell performance was studied directly in p–i–n cells prepared on textured ZnO. Solar cell efficiencies up to 9% were achieved at deposition rates of 5–6 A/s for the i-layer using high plasma powers. Applied as bottom cell in a-Si:H/μc-Si:H tandem cells a stable cell efficiency of 11.2% could be obtained. The excellent homogeneity was proven by the realization of first modules with an aperture area of 689 cm 2 and an active area initial efficiency of 10.3% (stable: 8.9%) using an established base technology for laser patterning and back contact sputtering at RWE Solar GmbH.

Texture etched Al-doped ZnO: a new material for enhanced light trapping in thin film solar cells

We found that sputtered ZnO:Al films with an appropriate compact structure develop a surface texture during etching in diluted HCl with excellent optical and light trapping properties. Moreover, these texturable films have a high optical transmission and good electrical properties which are not affected by the etching process. An analysis of the film structure by HRSEM is presented. High short-circuit currents have been achieved for a-Si:H solar cells incorporating these films as TCO substrates.

Amorphous and Microcrystalline Silicon Based Solar Cells and Modules on Textured Zinc Oxide Coated Glass Substrates

This paper addresses scientific and technological efforts to develop highly efficient silicon thin film solar modules on glass substrates. We present a comprehensive study of μc-Si:H p-i-n single junction and a-Si:H/μc-Si:H stacked solar cells prepared by plasma-enhanced chemical vapour deposition (PECVD) at 13.56 MHz excitation frequency. In the first step cell development was performed in a small area PECVD reactor showing the relationship between deposition process and resulting solar cell performance. Subsequent up-scaling to a substrate area of 30×30 cm 2 confirmed the scalability to large area reactors. Moreover, we developed textured ZnO:Al films by sputtering and post deposition wet chemical etching as front contact TCO-material with excellent light scattering properties. A-Si:H/μc-Si:H tandem cells developed on this textured ZnO yielded stable efficiencies up to 11.2 % for a cell area of 1 cm 2 . First solar modules were prepared in our recently installed process technology, which includes PECVD, sputtering, texture etching and laser scribing on substrate sizes up to 30x30 cm 2 . Initial module efficiencies of 10.8 % and 10.1 % were achieved for aperture areas of 64 cm 2 and 676 cm 2 , respectively.

Large area deposition of intrinsic microcrystalline silicon for thin film solar cells

This paper addresses the development of intrinsic /spl mu/c-Si:H films on 30/spl times/30 cm/sup 2/ substrate size as an intermediate step towards industry-size substrates (typically -1 m/sup 2/) by PECVD using 13.56 MHz excitation frequency. The authors succeeded in preparing high quality /spl mu/c-Si:H i-layers with good homogeneity over 27/spl times/27 cm/sup 2/. The corresponding deposition rates were 4-11 /spl Aring//s. The excellent material quality of these intrinsic /spl mu/c-Si:H films was proven by small area (1 cm/sup 2/) p-i-n solar cells with 8.1 and 6.6% efficiency at deposition rates of 5 and 10 /spl Aring//s, respectively. The doped layers of these cells were prepared in a small area PECVD reactor.

Up-scaling and optimization of thin-film solar cells and modules based on amorphous and microcrystalline silicon

This paper reviews the status of the process development and up-scaling of thin-film solar cells and modules based on amorphous (a-Si:H) and microcrystalline (/spl mu/c-Si:H) silicon at the Institute of Photovoltaics (IPV) on substrate areas up to 30/spl times/30 cm/sup 2/. Initial efficiencies of 10.6% and 10.7% were achieved for a-Si:H//spl mu/c-Si:H modules on 30/spl times/30 cm/sup 2/ and 10/spl times/10 cm/sup 2/ substrates, respectively. The latter ones yielded a stabilized efficiency of 10.1% which was independently confirmed by NREL. We address the process development for /spl mu/c-Si:H solar cells in a high pressure regime using plasma excitation frequencies of 13.56 and 40.68 MHz. High deposition rates up to 15 /spl Aring//s could be achieved by applying high discharge powers at 40.68 MHz. We discuss technological aspects related to the up-scaling of the PECVD processes to areas of 1 m/sup 2/ and above which is the topic of a recently started German R&D project of Applied Films GmbH & Co. KG (AF), Forschungsund Applikationslabor Plasmatechnik GmbH (FAP) and the IPV.