Trap States and Charge Transport Mechanisms in Small Molecule TADF Materials with Different Donor-Acceptor Structures

Abstract

Thermally Activated Delayed Fluorescence (TADF) materials have attracted significant attention due to their ability to achieve 100% internal quantum efficiency by simultaneously harvesting both singlet and triplet excitons during electroluminescence (EL) processes. Although the unique property has enabled their widespread application in organic lightemitting diodes (OLEDs), their device performance frequently suffers from imbalanced charge transport and trap-induced non-radiative recombination losses. Herein, we develop a synergistic strategy combining donor-acceptor molecular engineering with trap-state dilution to regulate charge injection and recombination in TADF-based OLEDs. A series of tailored D-A emitters reveals that acceptor units dominate electron-transport behavior while donors control hole mobility, thereby enabling the identification of BPAPTC as an optimal balanced-transport emitter. Further incorporation of BPAPTC into a wide-bandgap host effectively suppresses electron trapping, where reducing the dopant concentration simultaneously decreases trap density and improves carrier balance. The optimized device employing 20 wt% doping concentration achieves an external quantum efficiency of 13.22% along with markedly enhanced power efficiency and current efficiency. This work clarifies the structure-transport-trap correlations in TADF systems and provides practical design guidelines for high-efficiency OLEDs.