Does the band gap calculated from the photocurrent of Schottky devices lead to erroneous results? Analysis for CdTe

In recent years there has been an increased interest in flexible, lightweig ht photovoltaic modules based on thin metallic substrates. This paper repor ts some optoelectronic properties of electrodeposited CdTe thin films grown onto lightweight stainless steel (SS) foils. The optoelectronic properties were investigated with Schottky barriers of Au/CdTe/SS structure. The infl uence of the built-in potential of the Schottky junction on the bulk and th e interface recombination of the photo-generated minority carriers is expla ined with the existing models. The voltage-dependent collection functions i nfluence the photocurrent of the devices in both short- and long-wavelength regions of the spectrum. It is observed that in the photovoltaic mode the contribution due to the collection functions depends on the open-circuit vo ltage of the device. Au/CdTe Schottky devices, having higher open-circuit v oltage, exhibit a better response in the long wavelength region. This is du e to the efficient collection of the carriers generated in the bulk of the film and in such devices the contribution from the bulk collection function is higher. The enhancement in the bulk collection function causes a shift in the response of the device to higher wavelengths giving lower values for the calculated band gap. Due to this dependence of the long wavelength res ponse on the open-circuit voltage of the devices, the band gap calculated f rom the photocurrent of different Schottky devices gives different values f or the band gap of the material. Thus the method of calculating the band ga p from the photocurrent of Schottky devices can lead to erroneous conclusio ns regarding the band gap of the material.