Postdeposition Ligand Exchange Allows Tuning the Transport Properties of Large‐Scale CuInSe2 Quantum Dot Solids

• Published in: Advanced optical materials 2020-01, Vol.8 (1), p.n/a
• Main Authors: Gorris, Friederieke E. S., Deffner, Michael, Priyadarshi, Shekhar, Klinke, Christian, Weller, Horst, Lange, Holger
• Format: Article
• Language: English
• Subjects: Charge transport; Conductivity; Copper indium selenides; Electronic structure; Electrons; Exchanging; hopping transport; ligand exchange; Ligands; Materials science; Molecular structure; Optics; photocunductivty; quantum dot solids; Quantum dots; THz spectroscopy; Transport phenomena; Transport properties; Valence band
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.201901058

Colloidal quantum dots assembled into quantum dot solids usually suffer from poor conductivity. The most common charge transport mechanism through the solid is hopping transport where the hopping probability depends on the barrier type (stabilizing/connecting ligand molecule) and the interparticle distance. It is demonstrated that the electronic structure of the ligand molecule strongly alters the transport behavior through CuInSe2 quantum dot solids. Transport measurements and optical‐pump terahertz‐probe experiments after a ligand exchange to fully conjugated molecules show an increase of the conductivity by orders of magnitude, as well as a change of the hopping transport mechanism. This change is not due to a reduced interparticle distance, but the electronic structure: the obtained frequency‐dependent complex conductivities point toward an efficient hole transport enabled by an alignment of the quantum dot valence bands and ligand states. By exchanging the connecting molecules in quantum dot solids, the conductivity can be strongly enhanced. THz and transport studies show that not only the molecule length, but also its electronic structure is important: mobility increases by orders of magnitude can be achieved.