Unified Lifetime measurement for silicon PV

We present a unified lifetime measurement approach that enables self-consistent parameter-free determination of two lifetimes most frequently used in solar cell manufacturing, i.e. the excess carrier decay lifetime, τ_eff.d and the quasi steady-state effective lifetime, τ_eff. The approach uses the quasi-steady-state microwave detected photoconductance decay (QSS-μPCD) technique, whereby a small perturbation laser pulse excitation is imposed on a steady-state carrier excitation up to 25 suns. Quality of decay control, QDC, is a novel element critical for reliable measurement of τ_eff.d. It enables precise tuning of experimental conditions to achieve practically ideal mono-exponential decay conditions. Once the illumination characteristics of τ_eff.d are determined, the integration procedure of Schuurmans et.al. (1997) is used to determine the corresponding steady-state effective lifetime, τ_eff. Results correlate very well with QSSPC. Neither the measurement of τ_eff.d, nor the integration requires any wafer parameters, therefore, the determination of both lifetimes shall be considered a “parameter free” method.