Structurally simple non-doped sky-blue OLEDs with high luminance and efficiencies at low driving voltages

Abstract

Blue organic light-emitting diodes (OLEDs) are crucial for flat-panel displays and solid-state lighting. Regarding the practical application of OLEDs, high luminance and efficiencies at a low driving voltage, as well as a simple device structure, are highly desirable. However, blue OLEDs fulfilling these requirements are rare. Herein, two new sky-blue emitters, TPA-An-PPI and PCz-An-PPI, with the integration of wide-bandgap phenanthro[9,10-d]imidazole, anthracene and aromatic amine groups have been synthesized. They possess good thermal stability, bright emission in the solid state, as well as the bipolar carrier-transporting ability. Structurally simple non-doped sky-blue OLEDs with TPA-An-PPI as the emitting layer showed high performance, with the maximum luminance (L_max) of 51 390 cd m⁻², the maximum power efficiency (PE_max) of 10.42 lm W⁻¹, and the maximum external quantum efficiency (EQE_max) of 4.61%. More importantly, at a practical high luminance of 1000 cd m⁻², the PE and EQE retained high values of 8.48 lm W⁻¹ and 4.60%, respectively, and the corresponding driving voltage was as low as 3.6 V. The performance of the non-doped device based on PCz-An-PPI was also high, although being lower than that of TPA-An-PPI.