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

Copper iodide (CuI) is a promising -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 Se implantation with Se concentration varying between 0.50% and 6.50%. Hall effect measurements showed a ∼34% increase in electrical conductivity (σ ≈ 36.1 Ωcm) due to a ∼54% increase in carrier density (p ≈ 5.4 × 10 cm) in the -type γ-CuI film implanted with 5.0 × 10 Se.cm. A high Seebeck coefficient, α ≈ 388.9 μVK, and moderate electrical conductivity, σ ≈ 29.1 Ωcm, yield a nearly 85% increase in the power factor, ασ ≈ 439.7 μWmK, for a 1.0 × 10 Se.cm implanted film compared to the unimplanted film (ασ ≈ 236.4 μWmK). Monte Carlo simulation and density functional theory calculations revealed that the increased displacement per atom values and the {Se−} 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.