Pseudo FF and Voc analysis of Cz-Si Based Low Concentrator Solar Cells

Abstract

In this work, industrially feasible silicon based concentrator solar cells are characterized in dependence of the boron-oxygen-complex being in its active and idle state. The work emphasis on the concentration and therefore injection dependent behaviour of the open-circuit-voltage and pseudo fill factor. It is shown, that beside the usual logarithmic dependence of the open-circuit-voltage, an additional gain of 11 mV is achieved. Furthermore, a higher fill factor limit due to an increasing pseudo fill factor towards increasing irradiance is observed. The behaviour of both quantitiescan be described by the increasing injection of minority charge carriers diminishing the influence of the boron-oxygen-complex and other recombination channels with ideality factor greater than unity. This analysis shows that concentrator solar cells made of Czochralski grown silicon show a reduced sensitivity by means of this defect decreasing from 1.8 % at one sun to 0.6 % at 17 suns. Thus for concentrator applications, a boron-oxygen-limited bulk lifetime does not corrupt final cell performance to such an extent as for conventional, one-sun solar cells. Recent progress shows peak efficiencies for a metal-wrap-through concentrator solar cell architecture called AP-MWT of 21.1 % at two suns for a passivated emitter and rear solar cell device and over 20 % between five and twelvesuns for a device featuring a full area, Al alloyed contact on the rear.