title: Ligand coupling symmetry correlates with thermopower enhancement in small-molecule/nanocrystal hybrid materials.
abstract: We investigate the impact of the coupling symmetry and chemical nature of organic-inorganic interfaces on thermoelectric transport in Cu2-xSe 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(2)σ) 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 · K(2).
authors.affiliation: Materials Science Division, The Molecular Foundry, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Jared
authors.initials: J
authors.lastname: Lynch
authors.forename: Michele
authors.initials: M
authors.lastname: Kotiuga
authors.forename: Vicky V T
authors.initials: VV
authors.lastname: Doan-Nguyen
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Queen
authors.forename: Jason D
authors.initials: JD
authors.lastname: Forster
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Schlitz
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Murray
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Neaton
authors.forename: Michael L
authors.initials: ML
authors.lastname: Chabinyc
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Urban
keywords: composite; copper selenide; coupling; hybrid; ligand exchange; nanocrystal; organic; thermoelectrics