Measurement of the temperature-dependent recombination lifetimes in photovoltaic materials

Lifetime spectroscopy is a valuable tool for the characterization of photovoltaic materials. Measured lifetime values are inherently dependent on the defect and impurity densities present in the material. Injection-level and temperature dependencies of the recombination rate further characterize the material and possibly provide information for the identification of specific impurities. Also, trapping levels may be determined by observing their temperature-dependent thermal emission. Measured examples include surface-passivated, float-zone silicon and high-quality, undoped GaAs. Excess-carrier-decay curves are recorded from 80 to 300 K using a lifetime-measurement technique called ultrahigh frequency photoconductive decay.