Microcrystalline silicon for large area thin film solar cells

We present a comprehensive study of microcrystalline silicon (muc-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 X 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 Angstrom/s for the i-layer using high plasma powers. Applied as bottom cell in a-Si:H/muc-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. (C) 2002 Elsevier Science B.V. All rights reserved

Microbial Characteristics of Young Soils on Disposal Sites of Coal Combustion Waste in Bosnia and Herzegovina

Microbial communities are essential for a range of soil functions and adjust to soil development, environmental conditions and pollution level by community structure, abundance and activity. At desolated landfills of coal combustion waste (CCW) that were un-covered and covered with shallow soil material layers, soil microbial indicators were estimated for both the ecological and eco-toxicological evaluation. The young CCW sites with pH values of 9.5 and substantial coal-derived organic carbon showed significant microbial biomass content and nitrogen mineralization rates. At the 0 to 15 year old landfills, the microbial biomass content and activities increased significantly with age. However, large spatial variations occurred due to the variation of the cover material thickness, the degree of ash-aging and the tillage practices. Carbon dioxide was even sequestered at young CCW sites as indicated during laboratory incubation with an open apparatus purging continuously ambient air. In accordance, the respiratory quotient went down to 0.03 mol CO(2) evolution rate per mol O(2) uptake rate, indicating that the CO(2) evolution rate is limited as an overall quality indicator. Within 15 years, these 'Technosols' showed pH values of 7.7 and decalcified while changes in microbial biomass content and activity rates were mainly related to N availability. We concluded that the available As, B, Cr and Ni pollution at CCW sites seemed largely immobilised by organic matter and alkalinity and therefore did not to inhibit the microbial colonisation and development of high microbial activity within 15 years. However, the ash disposals pose a contamination risk by wind erosion and a future risk to human or environmental health when toxic metals will be released in soil at low pH values, low organic matter and low antagonistic ion contents