Inverse delta doping for improvement of solar cells

Delta doping with deep-level centers results in a marked decrease of open-circuit voltage and fill factor of photodiodes and solar cells when the doped layer is located near the crossover of electron and hole densities. The omission of recombination centers in a thin layer (inverse delta doping) at this position consequently causes an increase of the open-circuit voltage. The difficulty of improving the open-circuit voltage in actual high-efficient solar cells may have its origin in the inadvertent creation of donor-acceptor pairs caused by cross doping and consequent compensation. Such pairs are known to act as efficient recombination centers. The insertion of a thin, undoped inter1aye.r is proposed to separate donors and acceptors and thereby reduce the density of close pairs.