MINORITY-CARRIER DIFFUSION LENGTH DETERMINATION FROM CAPACITANCE MEASUREMENTS IN SE-CDO PHOTOVOLTAIC CELLS

In Se-CdO photovoltaic cells, the electron diffusion length L(n) 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 DELTA-I yields a straight line over a certain range of bias values. Extrapolation of this line to the 1/C axis yields L(n). It was found in the fabrication of the Se-CdO cells that increasing the substrate temperature from 100 to 140-degrees-C during the selenium deposition resulted in an increase in the cell photovoltaic output. Capacitance and DELTA-I 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.