The 'Fast' and 'Slow' Light Induced Defects in Diluted and Undiluted Hydrogenated Amorphous Silicon Solar Cells and Materials

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Studies have been carried out on a-Si:H p-in solar cells and corresponding i-layer films fabricated with and without hydrogen dilution for kinetics with high intensity and 1 sun illuminations. The results show a striking similarity between the kinetics in the fill factors (FF) of the p-in solar cells and the mobility lifetime (µτ) products of the corresponding i layer films. New results are presented on thermal annealing after 10 sun degradation which further substantiate the presence of fast and slow defects in the light induced changes of a-Si:H materials, as do the degradation kinetics of both cells and films under 1 sun illumination to their degraded steady states (DSS). Initial (fast) and subsequent (slow) regimes approaching DSS are present at temperatures between 25°C and 100°C, with the two regimes having distinctly different dependences on temperature. The DSS in the films and cells improve monotonically with temperature whereas the initial regimes show a clear reversal in their temperature dependence between 40°C and 50°C. The inability to express these results of 1 sun kinetics with rate equations containing only single time constants for creation and annealing provides further evidence that more than one defect is responsible for light induced degradation in a-Si:H materials and solar cells.

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