Water-soluble 1,2,4-triazole with diethylene glycol monoethyl ether groups: synthesis, characterization and application as an electron injection layer for PLEDs

Abstract

We designed a novel electron injection material 3OTAZ composed of an aromatic 1,2,4-triazolyl core with three diethylene glycol ether groups to enhance electroluminescence of PLEDs using the environmentally stable aluminum cathode. Multilayer PLEDs [ITO/PEDOT:PSS/HY-PPV/EIL(3OTAZ)/Al] using 3OTAZ as an electron injection layer (EIL) exhibit significantly enhanced device performance. The maximum luminous power efficiency and maximum luminance of the device with 3OTAZ as the EIL were enhanced to 0.34 lm W⁻¹ and 2970 cd m⁻², respectively, compared with those without an EIL (0.006 lm W⁻¹, 230 cd m⁻²). The turn-on voltage was also significantly reduced from 8.2 V to 4.3 V simultaneously. The performance enhancement has been attributed to improved electron injection which has been confirmed by the increase in the open-circuit voltage (V_oc) obtained from photovoltaic measurements. Moreover, more balanced charge injection and transport has been achieved by inserting 3OTAZ which adjusts the hole-blocking effect investigated by hole-only devices. The results indicate that 3OTAZ is an excellent electron injection candidate for performance enhancement of PLEDs using the high work-function Al cathode.