SPECTRAL RESPONSE OF LIGHT BIASED Si SOLAR CELLS AT OPEN CIRCUIT VOLTAGE

Spectral response (SR) is an effective tool for analyzing cell efficiency limiting factors: quantum efficiency, photocurrent and recombination parameters. A new method of SR determination which significantly expands the possibility of using this solar cell characteristic is proposed. In this method solar cell SR is determined and analyzed not only at short circuit conditions as usual but also under open circuit voltage conditions where light injected carrier concentration is significantly higher than in a short circuited cell. The SR determination is based on the measurement of AC current generated by a modulated spectral beam in a white light and, DC voltage, biased cell. The problem of AC current shunting by the forward voltage biased diode of the cell is solved by measurement corrections. A precise method of determining the correction coefficient, K, is based on the self calibration calculation procedure. Several groups of experimental solar cells were used for illustrating the advantages of the new method. The samples had structural defects of different types and of different spatial distributions in the base region. A wide range of variations of internal quantum efficiency (IQE), bulk lifetime, effective back surface recombination and photocurrent generated by AM 1.5 solar illumination were demonstrated by SR measurements of these samples when open or short circuited. 1