Enhancing the performance of Ga(In)NAs intermediate band solar cells

Intermediate band solar cells (IBSCs) have the potential to overcome the efficiency limit of single-bandgap solar cells. Dilute nitride III-V alloys, with splitting of the conduction band due to ban anticrossing, can be used as the intermediate band material for solar cell applications. In this work, we report on introduction of engineered GaInNAs alloy, with low (dilute) In and N contents, as IBSC material and comparison of performances of GaInNAs-based and corresponding In-free GaNAs-based IBSCs grown on GaAs(100) substrate. Introduction of a small amount of In (3%) in a GaN0.011As0.989-based IBSC was found to noticeably increase the short circuit current, Isc, at the expense of a small decrease in open circuit voltage, Voc. When annealed at 750 oC for 90 s, significant enhancements in Isc and Voc are seen, especially for the In-containing solar cell. The observed In-related enhancement in cells parameters after annealing is related to In-promoted bandgap tailoring and efficient curing of carriers traps during annealing. This occurred without change in the macroscopic composition of the GaInNAs alloy, most likely by In-N bonds formation on annealing, a phenomenon which does not exist in the GaNAs alloy.