Conventional and inverted organic light emitting diodes based on bright green emmisive polyfluorene derivatives

Abstract

Electro-active green light-emitting polymers based on polyfluorene derivatives (SF5 and SF6) were synthesized by Suzuki coupling reaction. Effect of fluorenone moiety on the main chain of the polyfluorene with allyl subunit was investigated against to performance of both inverted bottom emission and conventional organic light emitting diodes (IBOLEDs and OLEDs, respectively). 2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H- benzimidazole) (TPBI) was then utilized as an electron transport layer (ETL) to analyze the change in transport characteristics of the devices with a structure of ITO/PEDOT:PSS/polyfluorene/TPBI/Ca/Al. The results showed that efficiency enhanced nearly four times while the light output values were lowered with the insertion of TPBI as an ETL. In addition, IBOLEDs were also fabricated with a device architecture of ITO/ZnO/polyfluorene/V2O5 /Al being keen on backwards charge injection behavior of the polymers. IBOLEDs were fabricated by using synthesized zinc oxide (ZnO) as the electron-injecting layer. Luminance and luminous efficiency were significantly low while turn on voltages were too low with respect to the conventional devices fabricated. Further, annealing treatment were optimized for light output characteristics of the fabricated OLEDs. This study revealed the importance of charge transport feature of the synthesized polyfluorene derivatives in electroluminescent devices with variant architecture. (C) 2018 Elsevier Ltd. All rights reserved.