Efficient and ultra-high luminance orange-red organic light emitting diode (OLED) based on triphenylamine-benzothiadiazole-phenoxazine hybrid molecule with hybrid local and charge-transfer (HLCT) characteristic

Abstract

Due to the energy gap law, red emission needs relatively narrow energy gap, thus the nonradiative transition rate (knr) grows exponentially and eventually impacts the materials fluorescent efficiency. Here, an orange-red emission donor-acceptor-π-donor (D-A-π-D’) material N, N-diphenyl-4-(7-(4-(10-phenyl-10 H-phenoxazin-3-yl) phenyl) benzo [c] (Huang et al., 2019; Park et al., 2008; Caspar et al., 1982) [1,2,5] thiadiazol-4-yl) aniline (TBphPP) was designed and synthesized. Introducing a benzene π-bridge between the strong donor 10-phenyl-10H-phenoxazin (PPOX) and acceptor 2,1,3-benzothiadiazole (BTZ) not only is able to stretch the molecular conjugation so as to increase the proportion of LE state in hybrid local and charge-transfer (HLCT) state but also increase the overlap area of the electron cloud to improve luminous efficiency. As a result, the non-doped organic light-emitting diode (OLED) of TBphPP exhibited high luminance of 17,886 cd m−2 and relatively high exciton utilization efficiency (EUE) of 44 % with a standard red electroluminescent peak at 620 nm. Importantly, the optimized doped device based on TBphPP achieved high performance that the maximum external quantum efficiency (EQEmax) was up to 9.86 % with a higher EUE of 66.2 % and the efficiency roll-off (ηroll-off) at 100,000 cd m−2 was only 3.55 %. Simultaneously, it has reached ultra-high luminescence of 180,583 cd m−2, high current efficiency of 29.02 cd A−1 and power efficiency of 16.47 l m W−1. To our knowledge, the TBphPP device with such ultra-high luminance and high efficiency is one of the best performance orange-red materials based on HLCT characteristic.