Bis(2-(benzo[d]thiazol-2-yl)-5-fluorophenolate)beryllium: a high-performance electron transport material for phosphorescent organic light-emitting devices

Abstract

A beryllium complex, Be(FBTZ)₂ (HFBTZ: 2-(benzo[d]thiazol-2-yl)-5-fluorophenol), has been synthesized with the aim of developing electron transport materials (ETMs) for phosphorescent organic light-emitting diodes (PhOLEDs). The complex exhibits a high triplet energy of 2.62 eV which is able to confine triplet excitons of green or lower-energy emissive phosphorescent emitters within the emitting layer. Moreover, it possesses a low-lying LUMO energy level (−3.14 eV) allowing efficient electron injection and a high election mobility of 1.8–1.1 × 10⁻⁴ cm² V⁻¹ s⁻¹ for efficient electron transport. These characters enable Be(FBTZ)₂ to act as an excellent ETM in PhOLEDs. By using the complex as an electron transport layer (ETL), structurally simple green, yellow and red PhOLEDs exhibiting extremely low turn-on voltages (V_on) of 2.3, 2.1 and 2.2 V and high power efficiencies (PE) up to 65.0, 84.9 and 23.1 lm W⁻¹, respectively, have been successfully fabricated. Be(FBTZ)₂ can also work as a host material for PhOLEDs as demonstrated by a green device with a maximum PE of 42.8 lm W⁻¹ and a V_on value of 2.3 V.