Unraveling the Emission Pathways in Copper Indium Sulfide Quantum Dots

• Published in: ACS nano Vol. 15; no. 11; pp. 17573 - 17581
• Main Authors: Xia, Chenghui, Tamarat, Philippe, Hou, Lei, Busatto, Serena, Meeldijk, Johannes D, de Mello Donega, Celso, Lounis, Brahim
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23.11.2021
• Subjects: single dot spectroscopy; exciton self-trapping; fine structure; exciton−phonon coupling; exciton; core−shell nanocrystals
• ISSN: 1936-0851; 1936-086X; 1936-086X
• DOI: 10.1021/acsnano.1c04909

Semiconductor copper indium sulfide quantum dots are emerging as promising alternatives to cadmium- and lead-based chalcogenides in solar cells, luminescent solar concentrators, and deep-tissue bioimaging due to their inherently lower toxicity and outstanding photoluminescence properties. However, the nature of their emission pathways remains a subject of debate. Using low-temperature single quantum dot spectroscopy on core–shell copper indium sulfide nanocrystals, we observe two subpopulations of particles with distinct spectral features. The first class shows sharp resolution-limited emission lines that are attributed to zero-phonon recombination lines of a long-lived band-edge exciton. Such emission results from the perfect passivation of the copper indium sulfide core by the zinc sulfide shell and points to an inversion in the band-edge hole levels. The second class exhibits ultrabroad spectra regardless of the temperature, which is a signature of the extrinsic self-trapping of the hole assisted by defects in imperfectly passivated quantum dots.