UMG n-type Cz-silicon: Influencing Factors of the Light-induced Degradation and its Suitability for PV Production

Due to boron being present in compensated n-type silicon, minority carrier lifetime degrades under illumination. Lifetime reduction by light-induced degradation up to a factor of 16 was observed for illumination with 100 mW/cm2. In contrast to p-type, the degradation process in n-type does not follow a simple exponential trend. So this degradation process is time dependently investigated in this contribution. It is known that this process depends on a combination of light intensity and sample temperature, hence degradation is investigated independently and a separation of the influences was possible: a relation between light intensity and saturation value of normalized Cz defect concentration Nt*, and between sample temperature during illumination and defect generation rate will be presented. Furthermore it is shown that due to degradation the diffusion length of compensated n-type silicon in the degraded state is as low as in degraded p-type silicon. Finally it is shown that solar cells made from a compensated n-type crystal suffer from efficiency degradation.