Controlling the interfacial dipole via functionalization of quinoxaline-based small molecules for electron transport layer in organic light emitting diodes

Optoelectronic devices with organic semiconductors, such as organic light-emitting diodes (OLEDs), have received much attention because they offer ease of processing and device flexibility. However, practical application of these devices is still hindered by relatively poor device performance and lack of cost-effective fabrication process, which represent properties largely determined by the molecular dipole moments of the organic molecules. In this study, we designed and prepared novel quinoxaline-phosphine oxide small molecules (QPSMs) as the electron transport layer (ETL) for the solution-processable OLEDs by tuning the end functional group of the aromatic QPSMs. A key design criterion was controlling the dipole moments of QPSMs, which confers (1) convenient deposition on the emission layer without further annealing through solubility in isopropanol and (2) improved electron injection/transport behavior through effective band level matching of the devices. In particular, the optimized OLEDs with (4-(2,3-bis(4-methoxyphenyl)quinoxalin-5-yl)phenyl)diphenylphosphine oxide (MQxTPPO1) exhibit external quantum efficiency (EQE) of 6.12%. Our results demonstrate the potential application of QPSMs as next-generation ETLs in organic semiconductors.

Automated summary

In this study, novel quinoxaline-phosphine oxide small molecules were designed and prepared as the electron transport layer for organic light-emitting diodes (OLEDs). The dipole moments of the molecules were controlled by tuning the end functional group, which resulted in improved device performance. The optimized OLEDs exhibited an external quantum efficiency of 6.12%, demonstrating the potential application of these molecules as next-generation electron transport layers in organic semiconductors.