Evaluation of recombination processes using the local ideality factor of carrier lifetime measurements

The mechanisms that limit the performance of a solar cell can be often identified by an assessment of the solar cellʹs local ideality factor m. Typically, m is extracted from the current–voltage curve of a completed solar cell and plotted as a function of voltage. In this study, m is extracted from photoluminescence measurements of the effective carrier lifetime and plotted against the excess carrier concentration Δn or the implied open-circuit voltage Voci. It is shown that a plot of m(Δn) or m(Voci) is a powerful way to analyse recombination processes within a silicon wafer, where its main advantage is that it can be determined from wafers that have neither metal contacts nor a p–n junction. With an m(Δn) plot, one can readily identify a range of Δn (or voltage) that is dominated by a single recombination mechanism, or that constitutes a transition from one dominant mechanism to another. One can also identify the dominating recombination mechanisms at a cellʹs maximum power point. In this paper we demonstrate the application of extracting an m(Δn) curve, and we show how it is affected by Shockley–Read–Hall and Auger recombination in the bulk, and by fixed charge in a dielectric coating.