Version 2 2022-12-09, 14:06Version 2 2022-12-09, 14:06
Version 1 2022-12-08, 18:33Version 1 2022-12-08, 18:33
journal contribution
posted on 2022-12-09, 14:06authored byAleksandar Živković, Giuseppe Mallia, Helen E. King, Nora H. de Leeuw, Nicholas M. Harrison
Well designed and optimized epitaxial heterostructures
lie at the
foundation of materials development for photovoltaic, photocatalytic,
and photoelectrochemistry applications. Heterostructure materials
offer tunable control over charge separation and transport at the
same time preventing recombination of photogenerated excitations at
the interface. Thus, it is of paramount importance that a detailed
understanding is developed as the basis for further optimization strategies
and design. Oxides of copper are nontoxic, low cost, abundant materials
with a straightforward and stable manufacturing process. However,
in individual applications, they suffer from inefficient charge transport
of photogenerated carriers. Hence, in this work, we investigate the
role of the interface between epitaxially aligned CuO and Cu2O to explore the potential benefits of such an architecture for more
efficient electron and hole transfer. The CuO/Cu2O heterojunction
nature, stability, bonding mechanism, interface dipole, electronic
structure, and band bending were rationalized using hybrid density
functional theory calculations. New electronic states are identified
at the interface itself, which are originating neither from lattice
mismatch nor strained Cu–O bonds. They form as a result of
a change in coordination environment of CuO surface Cu2+ cations and an electron transfer across the interface Cu1+–O bond. The first process creates occupied defect-like electronic
states above the valence band, while the second leaves hole states
below the conduction band. These are constitutional to the interface
and are highly likely to contribute to recombination effects competing
with the improved charged separation from the suitable band bending
and alignment and thus would limit the expected output photocurrent
and photovoltage. Finally, a favorable effect of interstitial oxygen
defects has been shown to allow for band gap tunability at the interface
but only to the point of the integral geometrical contact limit of
the heterostructure itself.