Highly efficient green light emitting polyfluorene incorporated with 4-diphenylamino-1,8-naphthalimide as green dopant

Abstract

The dopant/host methodology, which enables efficient tuning of emission color and enhancement of the electroluminescence (EL) efficiency of organic light emitting diodes (OLEDs) based on small molecules, is applied to the design and synthesis of highly efficient green light emitting polymers. Highly efficient green light emitting polymers were obtained by covalently attaching just 0.3–1.0 mol% of a green dopant, 4-(N,N-diphenyl) amino-1,8-naphthalimide (DPAN), to the pendant chain of polyfluorene (the host). The polymers emit green light and exhibit a high photoluminescence (PL) quantum yield of up to 0.96 in solid films, which is attributed to the energy transfer from the polyfluorene host to the DPAN dopant unit. Single layer devices (device configuration: ITO/PEDOT/Polymer/Ca/Al) of the polymers exhibit a turn on voltage of 4.8 V, luminance efficiency of 7.43 cd A⁻¹, power efficiency of 2.96 lm W⁻¹ and CIE coordinates at (0.26, 0.58). The good device performance can be attributed to the energy transfer and charge trapping from the polyfluorene host to the DPAN dopant unit as well as the molecular dispersion of the dopant in the host. The device performance is fairly comparable to that of state-of-the-art green light emitting poly(fluorene-co-benzothiadiazole), indicating that the covalently attached dopant/host polymer system is very promising for the development of highly efficient electroluminescent polymers of tunable emission color.