Efficient organic light-emitting diodes based on iridium(iii) complexes containing indolo[3,2,1-jk]carbazole derivatives with narrow emission bandwidths and low efficiency roll-offs

Abstract

In this work, two cyclometalated ligands 2-(pyridin-2-yl)indolo[3,2,1-jk]carbazole (pyidcz) and 2-(4-(trifluoromethyl)pyridin-2-yl)indolo[3,2,1-jk]carbazole (tfpyidcz) containing an indolo[3,2,1-jk]carbazole unit were synthesized for achieving highly efficient iridium(III) complexes (pyidcz)₂Ir(tmd) and (tfpyidcz)₂Ir(tmd) (tmd = 2,2,6,6-tetramethyl-3,5-heptanedione). The two Ir(III) complexes exhibit emissions peaking at 499 and 554 nm, respectively, with narrow full width at half maximum (FWHM) values of 35 and 53 nm, respectively, short phosphorescence lifetimes less than 1 μs and high photoluminescence quantum yields of up to 90% in CH₂Cl₂ solution. The organic light-emitting diodes (OLEDs) with (pyidcz)₂Ir(tmd) and (tfpyidcz)₂Ir(tmd) emitters show good performances. The (pyidcz)₂Ir(tmd)-based device shows a turn-on voltage (V_on) of 3.6 V with a maximum brightness (L_max) of 39123 cd m⁻², a maximum current efficiency (η_c,max) of 69.2 cd A⁻¹, a maximum power efficiency (η_p,max) of 36.8 lm W⁻¹ and a maximum external quantum efficiency (EQE_max) of 21.2%. In particular, the FWHM bandwidth of the electroluminescence spectrum is only 33 nm, which was rarely reported for Ir(III) complex-based OLEDs. The performance of the (tfpyidcz)₂Ir(tmd)-based device is slightly better with a V_on of 3.3 V, a L_max of 31714 cd m⁻², a η_c,max of 78.4 cd A⁻¹, a η_p,max of 54.7 lm W⁻¹ and an EQE_max of 24.0%. Furthermore, the efficiency roll-offs of both devices are small, and the η_c values at 10 000 cd m⁻² brightness are still maintained at 60.0 and 71.4 cd A⁻¹, respectively, which provide a powerful reference for developing indolo[3,2,1-jk]carbazole-based Ir(III) complexes for efficient OLEDs.