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

The authors study the impact of the coupling symmetry and chem. nature of org.-inorg. interfaces on thermoelec. transport in Cu2-xSe nanocrystal thin films. By coupling ligand-exchange techniques with layer-by-layer assembly methods, the authors are able to systematically vary nanocrystal-org. linker interfaces, demonstrating how the functionality of the polar headgroup and the coupling symmetry of the org. linkers can change the power factor (S2σ) by nearly 2 orders of magnitude. Remarkably, ligand-coupling symmetry has a profound effect on thermoelec. transport in these hybrid materials. The authors 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. The authors' anal. indicates that ligand-coupling symmetry and binding mechanisms correlate with enhanced cond. approaching 2000 S/cm, and the authors employ this concept to demonstrate among the highest power factors measured for quantum-dot based thermoelec. inorg.-org. composite materials of ∼30 μW/m·K2.