Enhanced performance of organic light-emitting diodes by using PTB7 as anode modification layer

Poly[[4,8- bis[(2-ethylhexyl) oxy] benzo[1,2- b : 4,5- b'] dithiophene- 2,6- diyl][3- fluoro- 2-[(2- ethylhexyl) carbonyl] thieno[3, 4- b] thiophenediyl]] (PTB7) is used as an anode modification layer to fabricate organic light-emitting diode (OLED) with the configuration of ITO/PTB7 (with different concentrations)/NPB(40 nm)/ Alq 3 (60 nm)/ LiF(1 nm)/Al, and the effect of PTB7 concentration on the performance of device is investigated. The best concentration of PTB7 is 0.25 mg/mL, while the best device turn-on voltage is 4.3 V. For the best device, its maximum luminance is 45800 cd/m(2) at a driving voltage of 14.6 V, its maximum current efficiency is 9.1 cd/A, its turn-on voltage is reduced by 1.9 V and the maximum luminance is increased by 78.5% compared with that of the device without PTB7. The improvement of its performance is ascribed to the fact that the hole injection and transport ability are improved by the layer of PTB7.