PHOTOCURRENT CAPACITANCE METHOD OF DIFFUSION LENGTH MEASUREMENT

In the development of photovoltaic cells, it is helpful to monitor changes in the diffusion length of the minority carriers as fabrication changes are made. A convenient method of measurement of diffusion length in cells, where this quantity is relatively small, is the photocurrent-capacitance method. This method involves the measurement of the illuminated-to-dark photocurrent change of a cell illuminated with monochromatic bandgap light and junction capacitance as the applied reverse voltage bias is changed. Experiments with a CdO-Se heterojunction photovoltaic cell were carried out to optimize the experimental conditions of wavelength, monochromator slit width and light chopping frequency. It was shown that the method is simple and enables the variation of the diffusion length in the absorber layer to be followed as fabrication changes are made to the cell.