Study on the device structure of GaInNAs(Sb) based solar cells for use in 4-junction tandem solar cells

We have evaluated n-GaAs/i-GaInNAsSb/p-GaAs (nip) and p-GaAs/i-GaInNAsSb/n-GaAs (pin) solar cells grown by RF-molecular beam epitaxy. The absorption edges of these samples were at around 1180 nm. The currents generated in GaInNAs(Sb) layers, which were calculated from AM 1.5 spectrum and QE spectra at λ >; 870 nm region, were 4.6 (nip) and 5.1 (pin) mA/cm², respectively. Illuminated current voltage curves show that the open circuit voltages (V_oc) and FF values were 0.42 V and 0.71, respectively, for both structures. From these measurements, since almost the same PV properties are achieved for both samples, we found no distinct disadvantage to adopt nip structure substituted for pin GaInNAsSb solar cell, although there seems to be some difficulties in carrier collection near by the deep i-GaInNAsSb/p-GaAs interface in nip sample. We observed an enhancement in the filtered current density when GaInNAsSb absorber thickness is increased in nip structure without any degradation of other photovoltaic parameters. In order to further improve filtered current density, increase of GaInNAs(Sb) absorber thickness is necessary.