Cobalt (Ⅱ) oxide and nickel (Ⅱ) oxide alloys as potential intermediate-band semiconductors: A theoretical study

摘要

Solar cells based on single pn junctions, employing single-gap semiconductors can ideally achieve efficiencies as high as 34%. Developing solar cells based on intermediate-band semiconductors (IBSCs), which can absorb light across multiple band gaps, is a possible way to defy this theoretical limit and achieve efficiencies as high as 60%. Here, we use first principles quantum mechanics methods and introduce CoO and Co_(0.25)Ni_(0.75)O as possible IBSCs. We show that the conduction band in both of these materials is divided into two distinct bands separated by a band gap. We further show that the lower conduction band (i.e., the intermediate band) is wider in Co_(0.25)Ni_(0.75)O compared with CoO. This should enhance light absorption from the valence band edge to the intermediate band, making Co_(0.25)Ni_(0.75)O more appropriate for use as an IBSC. Our findings provide the basis for future attempts to partially populate the intermediate band and to reduce the lower band gap in Co_(0.25)Ni_(0.75)O in order to enhance the potential of this material for use in IBSC solar cell technologies. Furthermore, with proper identification of heterojunctions and dopants, CoO and Co_(0.25)Ni_(0.75)O could be used in multi-color light emitting diode and laser technologies.