Preparation of New Hyperbranched Polymers for Application in Light Emitting Diodes

Abstract
In organic light-emitting devices, harvesting excited triplet excitons for light emission is essential for achieving highly efficient electroluminescent (EL) devices. Recently, emitting materials with thermally activated delayed fluorescence (TADF) properties have received much attention as a modern class of highly efficient emitters. This is because they have properties that enable the harvesting of both singlet and triplet excitons, without the need for the exploitation of heavy metals. TADF materials have made considerable progress for use in OLEDs; however, most emitters are deposited via thermal evaporation under a vacuum and utilise small molecules. Despite its advantages, vacuum deposition is unscalable because of high fabrication costs. In contrast, polymer materials can be fabricated using solution techniques such as spin-coating and ink-jetting, offering notable advantages such as ease of processing, cost-effectiveness and scalability. Herein, solution-processable hyperbranched polymers (HBPs) incorporating derivatives of non-conjugated SiCz-based hosts and PXZ-TRZ-derivative TADF green emitters were synthesised and characterised through several techniques. A three-dimensional (3D) hyperbranched architecture enhances solubility, reduces intrinsic viscosity, suppresses aggregation-caused quenching (ACQ) and stabilises emission, while the non-conjugated system facilitates through-space charge transfer (TSCT) and a high triplet energy, preventing direct charge transfer between donor and acceptor moieties via conjugation length disruption.