First Principles Study of the Structural and Electronic Properties of the ZnO/Cu<sub>2</sub>O Heterojunction

Abstract

Many materials have been used in nanostructured devices; the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Heterojunctions based on ZnO/Cu 2 O oxides have recently emerged as promising materials for high-efficiency nanostructured devices. In this work, we are interested in the characterization of the surface and interface through nanoscale modeling based on ab initio (Density Functional Theory (DFT), Local Density Approximation (LDA), Generalized Gradient Approximation (GGA-PBE), and Pseudopotential (PP)). This study aims also to build a supercell containing a ZnO/Cu 2 O heterojunction and study the structural properties and the discontinuity of the valence band (band offset) from a semiconductor to another. We investigate crystal terminations of ZnO (0001) and Cu 2 O (0001). We calculate the energies of the polar surfaces and the work function in the c-axis for both oxides. We built a zinc oxide layer in the wurtzite structure along the [0001] direction, on which we placed a copper oxide layer in the hexagonal structure (CdI 2-type). We choose the method of Van de Walle and Martin to calculate the energy offset. This approach fits well with the DFT. Our calculations give us a value that corresponds to other experimental and theoretical values.

Heteroepitaxial Cu2O thin film solar cell on metallic substrates

“…4b shows that the film has a smooth surface morphology, but there are a few of surface pores. The dominant growth mechanism of Cu 2 O films on STO should be either three-dimensional (3D) island (Volmer-Weber, V-W)2435 or two-dimensional layer-by-layer followed by 3D island (Stranski-Krastanov, S-K) growth modes considering their surface energy (γ STO  ~ 0.8 ~ 1.6 J/m 2 , γ Cu2O  ~ 0.8–1.7 J/m 2 )3637 and lattice mismatch (~8.6%). So, the surface pores could be caused by incomplete coalescence during film growth via V-W or S-K growth mechanism with increasing the film thickness.…”