Study on electroluminescent characteristics of two novel fluorene/carbazole copolymers

The electroluminescent (EL) characteristics of two novel fluorene/carbazole copolymers are reported in the paper. Four devices with different structures were fabricated. The polymeric organic thin films were prepared by spin-coating technique. The electroluminescent characteristics of devices were investigated. The results showed that the EL spectra peaks of the devices without bathocuproine (BCP) layer were all located at the region of 520 nm±5 nm, which showed that light emission came from Alq3, and polymers here played only the role as hole transporting layer (HTL). The maximum luminance of these two devices was 1831 cd/m2. The EL spectra peaks of the devices with bathocuproine (BCP) layer were almost located at 425 nm, which were consistent with the characterizing spectrum of copolymers, indicating that the polymer films were emitting layers in the device structures. Alq3 acted here only as electron transporting layer (ETL).The maximum luminance of these devices were 1416cd/m2 for PFC1 and 1208 cd/m2 for PFC2. It was concluded that the inserting of bathocuproine (BCP) layer changed the recombination zone of excitons in devices and thus changed the emitting site. These two copolymers can be used not only as alternative HTL materials, but also as promising emitting materials for blue light OLEDs.