Thin Film Polycrystalline Si Solar Cells Studied in Transient Regime by Optical Pump Terahertz Probe Spectroscopy

We used time resolved terahertz spectroscopy to study ultrafast photoconductivity of polycrystalline thin film silicon solar cells. We selected a series of samples, which exhibited variable conversion efficiencies due to hydrogen plasma passivation under various technological conditions. The decay of the transient terahertz conductivity shows two components the fast one is related to the charge recombination at interfaces while the slow nanosecond one is attributed to the trapping of photocarriers by defects localized at grain boundaries or at dislocations in the polycrystalline p layer of the structure. We observed a clear correlation between the open circuit voltage and the nanosecond scale decay time of the transient terahertz conductivity of the solar cells. Thus the terahertz spectroscopy appears to be a useful contactless tool for inspecting the local photoconductivity of solar cells including in particular various nanostructured scheme