Experimental Synthesis and Properties of Metastable CuNbN2 and Theoretical Extension to Other Ternary Copper Nitrides

Andriy Zakutayev, Stephan Lany, David Ginley, Amy Allen, Xiuwen Zhang, Julien Vidal, Zhiming Cui, Minghui Yang, Francis DiSalvo

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52 Scopus Citations

Abstract

Copper nitrides are defect-tolerant semiconductors with properties that are promising for solar energy conversion applications. Currently, there are few known ternary copper nitride materials. Here, we synthesized a previously unreported CuNbN2 using an ion-exchange reaction and subsequently determined its properties. CuNbN2 has a layered delafossite-type structure with NbN6 octahedra arranged in layers separated by linear N-Cu-N bonds. Experimental measurements and theoretical calculations agree that CuNbN2 has a 1.3-1.4 eV optical absorption threshold; theory also indicates that the lowest energy indirect band gap is 0.9 eV. The calculated CuNbN2 electron and hole effective masses are quite isotropic (mout /min = 1.3-2.1) and low (m = 0.3-0.7 me), as for the layered crystal structure. On the basis of these results, we propose a new lattice-matched delafossite tandem solar cell approach with Cu(Nb,Ta)N2 absorbers, p-type CuAlO2 contacts, and n-type ZnO contacts. Interestingly, first-principles calculations indicate that CuNbN2 is thermodynamically unstable with respect to disproportionation, yet the successful synthesis and potentially useful photovoltaic properties of this metastable material are possible. We theoretically examine a wide range of ternary copper nitrides for thermodynamic stability and optoelectronic properties with the goal of accessing their potential for solar energy conversion. It is found that the majority of these materials are thermodynamically unstable but that some of them should have properties that are promising for solar energy conversion applications and thus are worth experimental synthesis attempts.

Original languageAmerican English
Pages (from-to)4970-4977
Number of pages8
JournalChemistry of Materials
Volume26
Issue number17
DOIs
StatePublished - 9 Sep 2014

Bibliographical note

Publisher Copyright:
© 2014 American Chemical Society.

NREL Publication Number

  • NREL/JA-5K00-62597

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