Effects of Side Groups on Kinetics of Charge Carrier Recombination in Dye Molecule-Doped Multilayer Organic Light-Emitting Diodes

TL;DR

This study investigates how different dye molecule structures affect charge recombination kinetics and efficiency in multilayer OLEDs, revealing that molecular design influences device performance.

Contribution

It provides new insights into the relationship between dopant molecular structure and charge recombination dynamics in OLEDs.

Findings

Recombination coefficient varies with molecular structure.

Donor groups and π-conjugation enhance recombination and efficiency.

Different dye derivatives show distinct EL efficiencies despite similar spectra.

Abstract

The kinetics of the charge carrier recombination in dye molecule-doped multilayer organic light-emitting diodes (OLEDs) was quantified by transient electroluminescence (EL). Three sets of dye molecules, such as derivatives of naphthalimide and stilbene, were used as dopants in light-emission layer. Although the devices show almost the same EL spectra for each set of molecules, they show very different EL efficiency. The difference in EL efficiency was attributed to the difference in charge carrier recombination, as revealed by transient EL. The recombination coefficient ({\gamma}) was determined from the long-time component of the temporal decay of the EL intensity after a rectangular voltage pulse was turned off. It was found that {\gamma} and EL efficiency were both strongly dependent on the molecular structures of the dopants, and the donor groups and {\pi}-conjugated structure guaranteed high {\gamma} and EL efficiency in OLEDs.