Three-dimensional hole transport in nickel oxide by alloying with MgO or ZnO

Abstract

It has been shown previously that the movement of a hole in nickel oxide is confined to two dimensions, along a single ferromagnetic plane. Such confinement may hamper hole transport when NiO is used as a p-type transparent conductor in various solar energy conversion technologies. Here, we use the small polaron model, along with unrestricted Hartree-Fock and complete active space self-consistent field calculations to show that forming substitutional MxNi1−xO alloys with M = Mg or Zn reduces the barrier for movement of a hole away from the ferromagnetic plane to which it is confined. Such reduction occurs for hole transfer alongside one or two M ions that have been substituted for Ni ions. Furthermore, the Mg and Zn ions do not trap holes on O sites in their vicinity, and NiO's transparency is preserved upon forming the alloys. Thus, forming MxNi1−xO alloys with M = Mg or Zn may enhance NiO's potential as a p-type transparent conducting oxide, by disrupting the two-dimensional confinement of holes in pure NiO.

Dynamics of Photoexcited Small Polarons in Transition-Metal Oxides

“…It can quench by recombining with the opposite charges. While the dynamics of charge-doping-induced ground-state polarons has already been studied in many TMOs, ,− due to the complexity, the behavior of photoexcited polarons in TMOs is still unclear.…”

Novel Solar Cell Materials: Insights from First-Principles

“…The band structure of NiO would need to be modified appropriately via suitable alloying, while preserving its favorable CT character, if NiO is to be employed as a light absorber. Given that prior studies have demonstrated good miscibility of Li 2 O, MgO, and ZnO within the NiO lattice, Alidoust et al , explored the influence of these alloying partners on the band structure and transport properties of NiO.…”

“…Copyright 2014 Wiley-VCH Verlag GmbH & Co. Panels d and e adapted from ref . Copyright 2015 American Institute of Physics.…”

“…(c) Spin configurations iv, v, and vi considered in Mg- and Zn-doped NiO (see text for explanation). Adapted from ref . Copyright 2015 American Institute of Physics.…”

“…For example, NiO’s intrinsic p-type nature and the charge-transfer (CT) character of its electronic structure make it an excellent candidate for both TCO and tandem DSSC applications. Additionally, the unique band structure of CoO makes it a contender for IBPVs while FeO could be a component of cheap solar energy conversion devices. , Therefore, in section , we discuss the electronic structure of the pure oxides, namely, NiO (section ), , CoO (2.2), and FeO (2.3), identify their respective limitations, and devise strategies to engineer their corresponding band gaps via alloying/doping to improve optical properties. Also critical to PV applications is the separation of photogenerated carriers (electrons and holes) after light absorption and the efficient conduction of free carriers to external circuits to maximize electricity generated (section ).…”