title: Significant reduction in NiO band gap upon formation of Lix Ni1-x O alloys: applications to solar energy conversion.
abstract: Long-term sustainable solar energy conversion relies on identifying economical and versatile semiconductor materials with appropriate band structures for photovoltaic and photocatalytic applications (e.g., band gaps of ∼ 1.5-2.0 eV). Nickel oxide (NiO) is an inexpensive yet highly promising candidate. Its charge-transfer character may lead to longer carrier lifetimes needed for higher efficiencies, and its conduction band edge is suitable for driving hydrogen evolution via water-splitting. However, NiO's large band gap (∼ 4 eV) severely limits its use in practical applications. Our first-principles quantum mechanics calculations show band gaps dramatically decrease to ∼ 2.0 eV when NiO is alloyed with Li2O. We show that Lix Ni1-x O alloys (with x=0.125 and 0.25) are p-type semiconductors, contain states with no impurity levels in the gap and maintain NiO's desirable charge-transfer character. Lastly, we show that the alloys have potential for photoelectrochemical applications, with band edges well-placed for photocatalytic hydrogen production and CO2 reduction, as well as in tandem dye-sensitized solar cells as a photocathode.
authors.affiliation: Department of Electrical Engineering, Princeton University, Princeton, NJ 08540-5263 (USA).
authors.forename: Nima
authors.initials: N
authors.lastname: Alidoust
authors.forename: Maytal Caspary
authors.initials: MC
authors.lastname: Toroker
authors.forename: John A
authors.initials: JA
authors.lastname: Keith
authors.forename: Emily A
authors.initials: EA
authors.lastname: Carter
mesh_terms: D000497:Alloys / Q000737:chemistry; D008094:Lithium / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D012666:Semiconductors; D012993:Solar Energy
chemical_list: D000497:Alloys; D009532:Nickel; D008094:Lithium; C028007:nickel monoxide
keywords: band gap engineering; dye-sensitized solar cells; energy conversion; photocatalysis; photovoltaics