Mobility-Lifetime Product in Hydrogenated Amorphous Silicon

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Abstract
We report an analysis of the carrier loss process in time-of-flight experiments on amorphous silicon solar cells. The electron mobility-lifetime ( µτ) product is determined by a transitory immobilization of the carriers in deep traps. The carriers can be recovered and collected when the experiment is extended into the ms time range. The collection efficiency is shown to depend on the occupation of gap states. We discuss the discrepancy between µτ values obtained from time-of-flight and photoconductivity measurements and present an analysis which relates the time-of-flight µτ products to the density of shallow and deep states in a-Si:H.