Resistive and photoconductive effects in spectral response measurements

It is shown that AC spectral response measurements done under DC bias voltage and bias illumination can include nonnegligible modulation effects from the series resistance of the device under test. The modulation effects change both the shape and the magnitude of the spectral response curve as a function of bias voltage and bias illumination. It is shown how high-efficiency CuInSe₂/CdS devices exhibit this kind of behavior and how to correct for it. By analyzing the spectral response of CuInSe₂/CdS devices as a function of voltage bias, a value of the series resistance is extracted which agrees with that derived from I-V measurements.