Solution-processing has the potential to reduce the cost and energy requirements in the fabrication of organic light-emitting diode (OLED) devices. In non-doped emissive layers, polymers are commonly used but often suffer from batch-to-batch variation. Oligomers, which have precise molecular structures, avoid this problem but maintain the favourable film-forming properties that polymers possess. We present three benzothiadiazole-containing fluorene-based oligomers, BT-F32, BT-F42 and BT-F52, which have terfluorene, quaterfluorene and pentafluorene arms, respectively, attached to a benzothiadiazole core. The materials show very high photoluminescence quantum yields, with BT-F42 exhibiting the highest PLQY of 0.96 in the thin film. Although there is little change in the electroluminescence spectra, the oligomer size influences device performance. BT-F32 had an external quantum efficiency of 1.9 % and high luminance whilst BT-F42 reached an external quantum efficiency of 2.3 %. Furthermore, the stability of the OLED devices was evaluated and showed that the device lifetime decays with increasing molecular length.
|Published - 7 Dec 2022