High efficiency and low efficiency roll-off hole-transporting layer-free solution-processed fluorescent NIR-OLEDs based on oligothiophene-benzothiadiazole derivatives

We report on simple low band-gap D-A-D type chromophores comprising triphylamine as a donor and oligothiophene-benzothiadiazoles as an acceptor. In the solid state, they exhibited strong near-infrared (NIR) emission with high fluorescence quantum yield when doped in the CBP host and low lying HOMO levels suitable for hole-transporting NIR fluorescent emitters for organic light-emitting diodes (OLEDs). Simple hole-transporting layer free solution-processed double-layer OLEDs (ITO/PEDOT:PSS (40 nm)/EML (60 nm)/TPBi (35 nm)/LiF (0.5 nm):Al (150 nm)) demonstrated NIR emission (702-758 nm) with an excellent maximum EQE of 1.52%, low efficiency roll-off and high maximum radiance of 4463 mW Sr-1 m(-2), which is amongst the best performance for NIR-OLEDs based on organic fluorescent materials.