Significant Reduction in NiO Band Gap Upon Formation of LixNi1−xO alloys: Applications To Solar Energy Conversion

Authors

  • Nima Alidoust,

    1. Department of Electrical Engineering, Princeton University, Princeton, NJ 08540-5263 (USA)
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  • Dr. Maytal Caspary Toroker,

    1. Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08540-5263 (USA)
    2. Present address: The Schulich Faculty of Chemistry, Technion, Israel Institute of Technology, Haifa 32000 (Israel)
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  • Dr. John A. Keith,

    1. Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08540-5263 (USA)
    2. Present address: Department of Chemical and Petroleum Engineering, Swanson School of Engineering , University of Pittsburgh , 804 Benedum Hall, 3700 O'Hara Street, Pittsburgh, NJ 15261 (USA)
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  • Dr. Emily A. Carter

    Corresponding author
    1. Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08540-5263 (USA)
    2. Program in Applied and Computational Mathematics and Andlinger Center for Energy and the Environment, Princeton University, Princeton, NJ 08540-5263 (USA)
    • Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08540-5263 (USA)

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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 LixNi1−xO 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.

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