Efficient fluorescent OLEDS based on assistant acceptor modulated HLCT emissive state for enhancing singlet exciton utilization

Abstract

Phenylamine phenanthroimidazole based bipolar compounds with donor–acceptor (D–A) architecture namely, 4-(1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-6,9-di(pyren-4-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenylaniline (DDPPPA) and 4′-(1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-6,9-di(pyren-4-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (DDPBA) have been synthesized with highly fluorescent pyrene moieties at C6- and C9-positions. The C6 and C9 modification enhanced the thermal, photochemical and electroluminescent properties. Both molecules were employed as blue emitters in non doped organic light emitting devices (OLEDs) and show high performances due to hybridized local and charge-transfer properties. An OLED with DDPPPA/DDPBA emissive layer shows deep-blue emission with maximum external quantum efficiency (η_ex), current efficiency (η_c) and power efficiency (η_p) of 5.7/6.0%, 10.5/12.0 cd A⁻¹ and 8.3/9.2 lm W⁻¹, respectively. Both devices show high singlet exciton utilizing efficiency (η_s) of DDPPPA-31.33% and DDPBA-35.29%. The doped device m-MTDATA:DDPPPA/m-MTDATA:DDPBA shows maximum efficiencies of η_c −7.4/8.23 cd A⁻¹; η_p −5.8/6.13 lm W⁻¹; η_ex −4.72/5.63% (5 wt%):η_c −8.36/9.15 cd A⁻¹; η_p −6.32/6.65 lm W⁻¹; η_ex −4.86/5.45% (10 wt%):η_c −9.58/10.02 cd A⁻¹; η_p −7.8/8.25 lm W⁻¹; η_ex −5.96/6.25% (20 wt%). The doped device based on TAPC host TAPC:DDPPPA/TAPC:DDPBA exhibits maximum efficiencies of η_c −9.60/10.03 cd A⁻¹; η_p −7.81/8.26 lm W⁻¹; η_ex −5.96/6.25% (20 wt%).