Bandgap engineering achieved with doping superlattices

Tailoring bandgaps by introducing quantum wells into the intrinsic region of a solar cell has been shown to improve the energy conversion of these devices. Doping superlattices are a potential way to achieve sub-bandgap absorption in a photovoltaic device without the need to introduce additional materials or strain balancing. In this paper we investigate the inclusion of doping superlattices in between the base and emitter regions of a photodiode. External quantum efficiency measurements of these devices demonstrate increased absorption below the GaAs band edge with respect to a GaAs reference cell. AM0 Illuminated J-V measurements of these devices exhibited variable results with PN configuration resulting in 0.81 V open circuit voltage and 7.7 mA/cm² short circuit current density. Dark J-V curves show a negative differential resistance region indicating tunneling between the n and p doped regions of the doping superlattice. These results suggest that doping induced superlattices may be an effective way to promote subgap photocurrent in a single junction GaAs cell. Additionally, a subcell in a multi-junction stack could employ this structure utilizing the increased design flexibility as compared to conventional heterojunction quantum well solar cells.