Redistribution of Recombination Active Defects and Trapping Effects in Multicrystalline Silicon After Wet Thermal Oxidation
In this work we characterised recombination active defects in standard multicrystalline silicon block material by investigating the effect of a wet thermal oxidation step at 800 degC with fast temperature ramps on the effective lifetimes measured by the CDI and QSSPC methods. The average lifetime was significantly decreased by the oxidation step. An increase in the concentration of interstitial iron as well as an increase in the concentration of trapping centres after the oxidation step was observed. A detailed investigation revealed an increase in the recombination activity of grain boundaries. Modeling of measured carrier density profiles indicates that iron dissolves from precipitates in grain boundaries and diffuses into the grains during the process. It was found that iron represents a major part of the active defect concentration in the investigated multicrystalline material after the applied oxidation process
Analysis of performance limiting material properties of multicrystalline silicon
We present progress of the analysis of multicrystalline silicon and of improvements of our understanding of material related performance limits of solar cells. Aspects covered are advanced numerical simulation, experimental results on carrier lifetime distributions, detailed analysis of the defect luminescence spectrum, and findings about breakdown behaviour. Modelling of impurity redistribution, specifically iron, with respect to high temperature steps enlightens mechanisms governing the phosphorus diffusion and aluminium gettering in heterogeneous systems. Evidence of outdiffusion of metallic impurities from grain boundaries, after high temperature steps, is given by analysing spatially resolved carrier lifetime measurements. In addition to lifetime, we present defect luminescence spectra measured by photoluminescence spectroscopy, including an interpretation of the origin of a remarkably temperature stable emission line at 838 meV. Finally, defect luminescence is connected to the origin of pre-breakdown of solar cells at reverse bias, a topic which is of high interest especially in context with the increased usage of purified metallurgical grade silicon.
Prediction of Muscular Endurance (Work Performance) From Individual Differences in Initial and Post Training Increments in Static Strength
Forty college men were given tests for static strength and strength endurance prior to an isotonic strength training program. Experimental results indicate that individual differences in static strength are a poor criterion in the prediction of muscular endurance. Following an increase in static strength resulting from isotonic strength training pre-training static strength and post-training strength increments are not indicative of an individual's performance in a hand grip endurance activity.