Voc-improvement for high-efficiency solar cells

The open circuit voltage and fill-factor can be substantially reduced by excessive carrier recombination within the space charge region of the pn-junction of a solar cell. Such reduction is maximized when the recombination centers are located near the plane where n≃p, assuming similar recombination rates for electrons and holes. The omission of recombination centers in a thin layer (inverse delta-doping) at this position consequently causes an increase of the V _oc and fill factor. The relative V_oc-improvement decreases with increasing width of this interlayer, and the improvement ceases when the layer thickness exceeds the width of the space charge region. The difficulty of improving the open circuit voltage in actual devices may have its origin in the inadvertent creation of donor-acceptor pairs caused by cross-doping. Such pairs are known to act as efficient recombination centers. The insertion of a high purity interlayer via MBE is proposed for the reduction of such recombination centers