EDT in Quantum Dots & Optoelectronics

Colloidal quantum dots are synthesised with long insulating ligands that provide colloidal stability but impede charge transport. Exchange with EDT replaces these ligands with short, bifunctional anchors that both passivate surface traps and bridge neighbouring nanocrystals, tightening the interparticle distance in the film (Kagan et al., 1996).

In quantum dot light-emitting diodes the emissive layer is treated with EDT to replace long insulating ligands with short bifunctional ones. The thinner ligand shell and the bridged nanocrystals improve charge transport through the film while the photoluminescence of the core–shell nanocrystals is retained (Kagan et al., 1996).

Lead selenide nanocrystal films require tight interparticle coupling to transport charge carriers generated in the infrared. EDT treatment cross-links adjacent nanocrystals through its two sulfur donors, raising the film conductivity while preserving the quantum confinement that sets the absorption edge (Kagan et al., 1996).

As research shifts toward lead-free absorbers, silver bismuth sulfide quantum dots have been paired with EDT to build photovoltaic devices. The ligand improves film formation at low temperature and passivates surface states that would otherwise promote non-radiative recombination.

Exchange proceeds by associative displacement of the native ligand at the nanocrystal surface, followed by chelation of a second surface site by the free thiol. The five-membered chelate generated by EDT is thermodynamically favoured, which drives the reaction to completion even in dilute dispersions (Kagan et al., 1996).