TPE-diphenylamine derivatives as solution-processable hole injectors with better charge balance for organic light-emitting diodes

Charge injection and transport layers with optimum carrier transport properties are essential for stable and efficient organic light-emitting diode (OLED) devices. Herein, we report two tetraphenylethylene-diphenylamine derivatives, TPOMe and TPOSt having four and two methoxy substituents, respectively, and explore their potential as solution-processable hole injection layers (HILs) for OLEDs. Standard, Alq3-based green OLEDs with a simple device design were used to demonstrate the properties of the synthesized HILs, in comparison with a commercially available standard HIL, m-MTDATA. TPOMe-based device exhibited a current efficiency of 4.2 cd A⁻¹, while TPOSt-based device showed 3.81 cd A⁻¹ at 10 mA cm⁻². Both the above devices showed better performance compared to a control device fabricated with the standard HIL, m-MTDATA, which showed a relatively lower current efficiency value (1.70 cd A⁻¹ at 10 mA cm⁻²). Similarly, the maximum external quantum efficiency (EQE) of TPOMe (1.77%) and TPOSt (1.55%) were higher than that of the m-MTDATA-based device (1.40%). Although m-MTDATA device has better luminance and hole mobility compared to TPOMe and TPOSt devices, the optimum charge balance in the latter devices leads to better current efficiency and EQE.