Color-stable deep red-emitting OLEDs based on a soluble terpolymer containing fluorene, thiophene and benzothiadiazole units

A novel soluble terpolymer (P8FO-Th-BT) containing 9,9-dioctylfluorene, thiophene, and 2,1,3-benzothiadiazole units were synthesized by Still coupling reaction. The single layer and multi-layer organic light emitting diodes (OLEDs) based on P8FO-Th-BT was fabricated. A deep red-emission device with the configuration of ITO/poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS)/P8FO-Th-BT:N,N′-di(3-methylphenyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4-diamine (TPD) (weight ratio being 1:1)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP, 15 nm)/tris(8-hydroxyquinoline) aluminum (Alq3, 15 nm)/LiF(5 Å)/Al(150 nm) was obtained, and the maximum luminance was measured to be 226 cd/m2 at the bias voltage of 10 V. The electroluminescent peak located at 708 nm, and the spectrum covered both the red and infrared regions. Moreover, the Commission International De L’Eclairage (CIE) chromaticity coordinates of the device were inalterable when the bias voltage varied, which was beneficial to the application on display.