Enhancing external quantum efficiency in a sky-blue OLED by charge transfer via Si quantum dots

Abstract

Organic light-emitting diodes aim to achieve high efficiency by using excitons to achieve a 100% quantum efficiency (QE). However, developing functional organic materials for this purpose can be time-consuming. To address this challenge, a new method has been proposed to incorporate inorganic quantum dots into the organic luminescent layer to enable unlimited exciton formation and approach the 100% QE limit. Inorganic quantum dots are clusters of atoms that contain numerous thermally generated electrons and holes at conduction and valence bands. Immersed quantum dots act as charge generation centers, providing electrons and holes with unlimited amounts to form excitons. After radiative recombination, these excitons generate photons that cause internal QE to nearly 100%. This concept has been demonstrated using Silicon quantum dots (SiQDs) and phosphorescent materials. The average size of SiQDs is approximately 6 nm, and they are well-dispersed within the guest–host blue phosphorescent light-emitting materials. With only 5 × 10^–3% (in weight) of SiQDs in the precursor, external QE increased from 2 to 17.7%, nearly a nine-fold enhancement. The prolonged decay time from 1.68 to 5.97 ns indicates that electrons are transferred from SiQDs to the luminescent materials. This universal method can be applied to green and red emissions with various inorganic quantum dots in different organic luminescent material systems.