Defect and dopant complex mediated high power factor in transparent selenium-doped copper iodide thin films

Abstract

Copper iodide (CuI) is a promising p-type transparent thermoelectric material for near-room temperature energy harvesting. We report a high-power factor for selenium (Se)-doped CuI films. Ion beam-sputtered CuI films were doped using 30 keV 80Se+ implantation with Se concentration varying between 0.50% and 6.50%. Hall effect measurements showed a ∼34% increase in electrical conductivity (σ ≈ 36.1 Ω−1cm−1) due to a ∼54% increase in carrier density (pH ≈ 5.4 × 1019 cm−3) in the p-type γ-CuI film implanted with 5.0 × 1014 Se.cm−2. A high Seebeck coefficient, α ≈ 388.9 μVK−1−1, and moderate electrical conductivity, σ ≈ 29.1 Ω−1cm−1, yield a nearly 85% increase in the power factor, α2σ ≈ 439.7 μWm−1K−2, for a 1.0 × 1015 Se.cm−2 implanted film compared to the unimplanted film (α2σ ≈ 236.4 μWm−1K−2). Monte Carlo simulation and ab initio density functional theory calculations revealed that the increased displacement per atom values and the {SeI−VCu} defect complex-induced shallow acceptor could be attributed to the observed increase in hole density. Our results highlight that native defects and defect complexes are beneficial for enhancing the power factor in transparent CuI for thermoelectric applications.