Highly efficient blue polyfluorenes using blending materials as hole transport layer

Abstract

Abstract Efficient blue polyfluorenes have been generated by incorporating the hole transport material N-([1,1′-biphenyl]-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)- phenyl)-9H-fluoren-2-amine (BCFN) into poly(9,9-dioctylfluorene) (PFO) as an emissive layer. BCFN has an appropriate highest occupied molecular orbital (HOMO) energy level and high hole transport/electron barrier properties, which can effectively reduce the hole injection barrier and improve the charge carrier injection and transport. These properties resulted in a significant improvement in the electroluminescent (EL) performance of PFO. To further improve the EL performance of PFO, the blend hole transport layer, PVK [Poly(N-vinylcarbazole)]:BCFN with weight ratio of 3:7, was inserted between the PEDOT:PSS and the emissive layer. The blend hole transport layer effectively reduced exciton quenching and markedly decreased the hole injected barrier. A maximum luminous efficiency (LEmax) of 4.31 cd A−1 was obtained with the CIE coordinates of (0.17, 0.13). The device maintained a LEmax of 4.27 cd A−1 at a luminance of 1000 cd m−2. In addition, stable EL spectra were obtained and were nearly identical when the applied voltage was increased from 5 to 11 V. These results indicate that blending the appropriate hole transport material can be an efficient method to improve device performance based on the large band gap of blue-lighting materials.