Minority carrier diffusion length determination from capacitance measurements in Se–CdO photovoltaic cells

In Se–CdO photovoltaic cells, the electron diffusion length Ln in the selenium absorber layer has been determined from measurements of capacitance C and photocurrent under monochromatic illumination by variation of applied reverse bias. If penetrating incident light of band-gap wavelength is used, a plot against 1/C of the illuminated-to-dark current change ΔI yields a straight line over a certain range of bias values. Extrapolation of this line to the 1/C axis yields Ln. It was found in the fabrication of the Se–CdO cells that increasing the substrate temperature from 100 to 140 °C during the selenium deposition resulted in an increase in the cell photovoltaic output. Capacitance and ΔI measurements on these cells showed an increase in diffusion length with substrate temperature, indicating that the increased cell performance was due to improved electron collection in the selenium layer.