Stability of Amorphous Silicon Solar Cells with pin Structure
Solar cells made in our laboratory from hydrogenated amorphous Silicon with pin structure show an efficiency of up to 7,4% on 6 mm2 and up to 5% on 2″ x.2″. Degradation experiments with illumination and under forward bias in the dark, were performed. These measurements as well as capacitance and spectral response measurements show, that optically or electrically injected carriers induce recombination enhanced defect reactions, which lead to an increase of the density of states and, respectively, to a decrease of the,uτ -product, mainly of that of the holes. Compensation of the normally n-type i-layer by doping with Boron leads to higher cell stability due to a shifting of the Fermi level closer to midgap. The effect of different concentrations of Boron in the i-layer on its dark and photoconductivity was investigated. A maximum of photoconductivity is seen for 5 ppm. Preliminary tests on cells suggest, that the degradation can be minimized by a controlled Boron concentration of the i-layer.
KeywordsSolar Cell Amorphous Silicon Forward Bias Degradation Experiment Photovoltaic Solar
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