Photoluminescence: a surprisingly sensitive lifetime technique

Photoluminescence (PL) measurements in transient, quasi steady state and in an intermediate mode are used to determine the injection level dependent effective excess carrier lifetime τ_eff in silicon wafers. The effective lifetime is measured over a wide dynamic range and down to very small injection levels Δn < 10⁹ cm^-3, demonstrating that PL is a convenient and also a surprisingly sensitive lifetime technique. We show experimentally that PL measurements are not significantly affected by excess carriers accumulated in space charge regions in contrast to other lifetime techniques such as photoconductance (PC). With PL measurements on bifacial silicon solar cells it is also demonstrated experimentally that simultaneous measurements of PL and of the incident light intensity yield the equivalent of Suns-V_oc measurements, but in contact less mode and without the need for a solar cell structure.