Orthogonal colloidal quantum dot inks enable efficient multilayer optoelectronic devices

Seungjin Lee; Min-Jae Choi; Geetu Sharma; Margherita Biondi; Bin Chen; Se-Woong Baek; Amin Morteza Najarian; Maral Vafaie; Joshua Wicks; Laxmi Kishore Sagar; Sjoerd Hoogland; F Pelayo García de Arquer; Oleksandr Voznyy; Edward H Sargent

doi:10.1038/s41467-020-18655-7

Orthogonal colloidal quantum dot inks enable efficient multilayer optoelectronic devices

Nat Commun. 2020 Sep 23;11(1):4814. doi: 10.1038/s41467-020-18655-7.

Authors

Affiliations

¹ Department of Electrical and Computer Engineering, University of Toronto, 35 St George Street, Toronto, ON, M5S 1A4, Canada.
² Department of Chemical and Biochemical Engineering, Dongguk University, Seoul, 04620, Republic of Korea.
³ Department of Physical and Environmental Sciences, University of Toronto Scarborough, Scarborough, ON, M1C 1A4, Canada.
⁴ Department of Chemical and Biological Engineering, Korea University, 145 Anam-Ro, Seongbuk-Gu, Seoul, 02841, Republic of Korea.
⁵ Department of Physical and Environmental Sciences, University of Toronto Scarborough, Scarborough, ON, M1C 1A4, Canada. o.voznyy@utoronto.ca.
⁶ Department of Electrical and Computer Engineering, University of Toronto, 35 St George Street, Toronto, ON, M5S 1A4, Canada. ted.sargent@utoronto.ca.

^# Contributed equally.

Abstract

Surface ligands enable control over the dispersibility of colloidal quantum dots (CQDs) via steric and electrostatic stabilization. Today's device-grade CQD inks have consistently relied on highly polar solvents: this enables facile single-step deposition of multi-hundred-nanometer-thick CQD films; but it prevents the realization of CQD film stacks made up of CQDs having different compositions, since polar solvents redisperse underlying films. Here we introduce aromatic ligands to achieve process-orthogonal CQD inks, and enable thereby multifunctional multilayer CQD solids. We explore the effect of the anchoring group of the aromatic ligand on the solubility of CQD inks in weakly-polar solvents, and find that a judicious selection of the anchoring group induces a dipole that provides additional CQD-solvent interactions. This enables colloidal stability without relying on bulky insulating ligands. We showcase the benefit of this ink as the hole transport layer in CQD optoelectronics, achieving an external quantum efficiency of 84% at 1210 nm.