Characterization of amorphous silicon pin solar cells by transient measurement techniques

Abstract

In order to provide more specific access to solar cell limitations (and to faults during line production as well) the authors report on space-charge limited time-of-flight (SCL-TOF) studies in the voltage mode, and on forward bias transient switching experiments in 500 nm thick pin structures. Complementing I-V characteristics and quantum yield, both techniques are easy to use and give a clear and reproducible measure of the degradation state of a-Si:H based solar cells. An effective carrier lifetime can be deduced from the extraction time of SCL-TOF. Time and temperature dependent forward current transients show a distinct voltage threshold in the onset of double-injection recombination currents which is related to the built-in voltage of the devices. Enhanced bulk recombination due to light or current induced degradation reduces saturated forward currents and increases the time initially needed for building up space charge in the pin-diodes. Differences upon light-soaking by front or back side illumination have also been investigated.