Comparison of Techniques for Measuring Carrier Lifetime in Thin-Film and Multicrystalline Photovoltaic Materials

Rapid and contactless measurement of the recombination lifetime has become a very important issue in photovoltaics. The recombination lifetime is probably the most critical and variable parameter in photovoltaic materials. In this work, we will first develop the theory behind several of the more widely used techniques. The common methods include directly measuring the transient photo-induced excess carrier decay rate. The quasi-steady-state photoconductivity measures the excess conductivity during optical excitation. The carrier lifetime is calculated from the steady-state signal using algorithms that include carrier mobility and doping density. Time-resolved photoluminescence measures the photon emission signal as a function of time, after pulsed excitation. For polycrystalline materials, the influence of traps on the measurement will be analyzed. We will analyze data on a variety of samples using all of these techniques. The representative samples include thin-film and wafer silicon materials that are currently popular in the photovoltaic community. The correct analysis of lifetime data will be emphasized in this work.