Confinement Effects and Charge Dynamics in Zn3N2 Colloidal Quantum Dots: Implications for QD-LED Displays

Ruben Ahumada-Lazo; Simon M Fairclough; Samantha J O Hardman; Peter N Taylor; Mark Green; Sarah J Haigh; Rinku Saran; Richard J Curry; David J Binks

doi:10.1021/acsanm.9b01714

Confinement Effects and Charge Dynamics in Zn₃N₂ Colloidal Quantum Dots: Implications for QD-LED Displays

ACS Appl Nano Mater. 2019 Nov 22;2(11):7214-7219. doi: 10.1021/acsanm.9b01714. Epub 2019 Oct 28.

Authors

Ruben Ahumada-Lazo¹, Simon M Fairclough¹, Samantha J O Hardman¹, Peter N Taylor², Mark Green³, Sarah J Haigh¹, Rinku Saran¹, Richard J Curry¹, David J Binks¹

Affiliations

¹ Department of Physics and Astronomy and the Photon Science Institute, Department of Materials, Manchester Institute of Biotechnology, and Photon Science Institute, Department of Electrical and Electronic Engineering, The University of Manchester, Manchester M13 9PL, U.K.
² Sharp Laboratories of Europe Ltd, Edmund Halley Road, Oxford Science Park, Oxford OX4 4GB, U.K.
³ Department of Physics, King's College London, Strand, London, U.K. WC2R 2LS.

Abstract

Zinc nitride (Zn₃N₂) colloidal quantum dots are composed of nontoxic, low-cost, and earth-abundant elements. The effects of quantum confinement on the optical properties and charge dynamics of these dots are studied using steady-state optical characterization and ultrafast fluence-dependent transient absorption. The absorption and emission energies are observed to be size-tunable, with the optical band gap increasing from 1.5 to 3.2 eV as the dot diameter decreased from 8.9 to 2.7 nm. Size-dependent absorption cross sections (σ = 1.22 ± 0.02 × 10^-15 to 2.04 ± 0.03 × 10^-15 cm²), single exciton lifetimes (0.36 ± 0.02 to 0.65 ± 0.03 ns), as well as Auger recombination lifetimes of biexcitons (3.2 ± 0.4 to 5.0 ± 0.1 ps) and trions (20.8 ± 1.8 to 46.3 ± 1.3 ps) are also measured. The degeneracy of the conduction band minimum (g = 2) is determined from the analysis of the transient absorption spectra at different excitation fluences. The performance of Zn₃N₂ colloidal quantum dots thus broadly matches that of established visible light emitting quantum dots based on toxic or rare elements, making them a viable alternative for QD-LED displays.