Ligand Coupling Symmetry Correlates with Thermopower Enhancement in Small-Molecule/Nanocrystal Hybrid Materials

• Published in: ACS nano Vol. 8; no. 10; pp. 10528 - 10536
• Main Authors: Lynch, Jared, Kotiuga, Michele, Doan-Nguyen, Vicky V. T, Queen, Wendy L, Forster, Jason D, Schlitz, Ruth A, Murray, Christopher B, Neaton, Jeffrey B, Chabinyc, Michael L, Urban, Jeffrey J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 28.10.2014
• Subjects: COMPOSITES; COPPER SELENIDE; CRYSTAL STRUCTURE; ELECTRICAL CONDUCTIVITY; JOINING; LIGANDS; MICROSTRUCTURES; Nanocrystals; Nanostructure; Power factor; Symmetry; Thermoelectricity; THIN FILMS; Transport; coupling; nanocrystal; hybrid; thermoelectrics; composite; copper selenide; ligand exchange; organic
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/nn503972v

We investigate the impact of the coupling symmetry and chemical nature of organic–inorganic interfaces on thermoelectric transport in Cu2–x Se nanocrystal thin films. By coupling ligand-exchange techniques with layer-by-layer assembly methods, we are able to systematically vary nanocrystal–organic linker interfaces, demonstrating how the functionality of the polar headgroup and the coupling symmetry of the organic linkers can change the power factor (S 2σ) by nearly 2 orders of magnitude. Remarkably, we observe that ligand-coupling symmetry has a profound effect on thermoelectric transport in these hybrid materials. We shed light on these results using intuition from a simplified model for interparticle charge transport via tunneling through the frontier orbital of a bound ligand. Our analysis indicates that ligand-coupling symmetry and binding mechanisms correlate with enhanced conductivity approaching 2000 S/cm, and we employ this concept to demonstrate among the highest power factors measured for quantum-dot based thermoelectric inorganic–organic composite materials of ∼30 μW/m·K2.