PNNL

Abstract

Stable and efficient organic light emitting devices (OLEDs) are an integral part of the future of lighting and displays. The hole accumulation at the hole transport/emissive layer interface in such devices is considered to be a major pathway for degradation and efficiency loss. Here we report the design and synthesis of two charge-transporting host materials, based on the phosphine oxide (PO) moiety, engineered to improve hole transport of the emissive layer. The compounds are an extension of a molecular design strategy already explored and reported by our team which incorporates a hole transporting moiety and an electron transporting moiety. These novel materials were designed with two hole transport moieties (HTms) to further improve hole transport, compared to the first generation host materials that were designed with one hole transport functional group. The triplet exciton energy was maintained at a level greater than that of FIrpic (2.7 eV) to prevent exciton quenching. The EHOMO and ELUMO of the two classes of molecules (i.e., one HTm vs. 2 HTms) were similar, however their device performance varied greatly. Emission zone experiments were conducted to further understand the differences between molecules.