|Ligand Coupling Symmetry Correlates with Thermopower Enhancement in Small-Molecule/Nanocrystal Hybrid Materials
|Year of Publication
|Lynch, Jared, Michele Kotiuga, Vicky V. T. Doan-Nguyen, Wendy L. Queen, Jason D. Forster, R.A. Schlitz, Christopher B. Murray, Jeffrey B. Neaton, M.L. Chabinyc, and J.J. Urban
|composite, copper selenide, coupling, hybrid, ligand exchange, nanocrystal, organic, thermoelectrics
|We investigate the impact of the coupling symmetry and chemical nature of organic-inorganic interfaces on thermoelectric transport in Cu-2-Se-x 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 sigma) 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 similar to 30 mu W/m.K(2).