The Use of Injection-Level Dependent Lifetime Measurements for Determining Solar Cell Parameters

Abstract

The open-circuit voltage of a silicon solar cell is well known to be directly related to the effective recombination lifetime of the substrate as measured under 1-sun illumination. However, an important feature of the recombination lifetime is that it is dependent on the concentration of excess carriers present, often very strongly. This can result in a significantly lower recombination lifetime at maximum-power as compared to open-circuit conditions, and consequently cause a reduction in the cell fill factor. In high efficiency multicrystalline silicon cells, such a varying lifetime is often the result of impurities and defects residing in the bulk of the material. Injection-level dependent lifetime measurements on such wafers are shown to provide a good explanation of low fill factors observed in finished cells. The impact of these bulk recombination centres on fill factors in commercially produced multicrystalline silicon cells is modelled and discussed. Show more