Energy level of minority carrier trap centers induced by light illumination in B-doped Cz-Si solar cells

The conversion efficiency of boron (B)-doped Czochralski silicon (Cz-Si) solar cells are known to be decreased by light illumination or minority carrier injection. Some defects are induced by illumination and they act as trap centers, shorten the minority carrier (electron) lifetime. The energy level of this minority carrier trap centers were determined by analyzing the open-circuit voltage (V/sub OC/) changes as a function of temperature. When temperature is low, all electrons which are captured by the trap centers recombine with holes and they do not contribute to the generation of electric power. However, as the temperature is increasing, some of captured electrons are thermally excited to the conduction band before recombination process. Hence, the lifetime of minority carriers are improved and V/sub OC/ is recovered. Based on this result, to estimate the number of electrons captured by trap centers and the activation energy, the capture cross section is considered to depend on temperature. The energy level of trap center induced by light illumination is estimated to be 0.26eV, which corresponds to the boron-oxygen related defect (E/sub C/-0.26 V).