Impact of light-induced recombination centres on the current-voltage characteristic of Czochralski silicon solar cells

Abstract

We have investigated the effect of the light-induced deep-level recombination centre specific to boron-doped, oxygen-contaminated Czochralski (Cz) silicon on the current-voltage characteristic of Cz silicon solar cells by means of numerical simulation and experiment. The device simulation predicts the occurrence of a shoulder in the current-voltage curve after activating the characteristic recombination centre. The physical reason for the non-ideal diode behaviour, characterised by a local ideality factor greater unity, is the strongly injection-level-dependent bulk lifetime produced by the deep-level centre. The increased ideality factor causes a degradation in fill factor with the magnitude of degradation depending on the doping concentration of the Cz silicon base. In order to verify the theoretical predictions experimentally, we have performed measurements on high-efficiency Cz silicon solar cells. Current-voltage curves recorded before and after light degradation clearly show the theoretically predicted change in shape and the reduction in fill factor. An excellent quantitative agreement between calculation and experiment is obtained for the subtracted current-voltage curves measured after and before illumination.