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 CH2Cl2solution. 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 (Von) of 3.6 V with a maximum brightness (Lmax) of 39123 cd m−2, a maximum current efficiency (ηc,max) of 69.2 cd A−1, a maximum power efficiency (ηp,max) of 36.8 lm W−1and a maximum external quantum efficiency (EQEmax) 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 aVonof 3.3 V, aLmaxof 31714 cd m−2, aηc,maxof 78.4 cd A−1, aηp,maxof 54.7 lm W−1and an EQEmaxof 24.0%. Furthermore, the efficiency roll-offs of both devices are small, and theηcvalues at 10 000 cd m−2brightness 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.