Efforts to develop excess-carrier recombination lifetime measurement standards for silicon PV

The excess carrier recombination lifetime in silicon solar cells is a critical indicator of material and passivation quality. This property can be measured on silicon crystals and then at every stage of production. As the silicon PV field has developed, many methods of measuring this carrier lifetime are coming into use, including mapping methods such as microwave-photoconductance decay, imaging methods including infra-red carrier density imaging and photoluminescence, as well as the methods that measure lifetime vs. carrier density such as Quasi-Steady-State Photoconductance, (QSSPC). This paper will focus on efforts to define standards for the measurement of carrier lifetime in silicon that will allow for the comparison of results between these varied methods. As an example of the importance of comparisons between methods, the “trapping” signature often seen in photoconductance measurements is briefly discussed.