Boosting the performance of sky-blue fluorescent OLEDs based on DPA-containing electron-transporting materials with a “V-shaped layout of triplet energy levels”

Abstract

Here, using a strategy called “V-shaped layout of triplet energy levels (E_Ts)”, a high-T₁, electron-deficient and bulky 1,5-diazarcarbazole (15NCz) was first introduced for the construction of new electron-transporting materials (ETMs). When 9,10-diphenylanthracene (DPA) was encapsulated by 15NCz at different positions, a series of ETMs with high electron mobility and good thermal stability were designed and synthesized: 9-(4-(9-([1,1′-biphenyl]-4-yl)anthracen-10-yl)phenyl)-9H-1,5-diazarcarbazole (p-S15NCzDPA), 9-(3-(9-([1,1′-biphenyl]-3-yl)anthracen-10-yl)phenyl)-9H-1,5-diazarcarbazole (m-S15NCzDPA), 9,10-bis(4-(9H-1,5-diazarcarbazole-9-yl)phenyl)anthracene (p-D15NCzDPA) and 9,10-bis(3-(9H-1,5-diazarcarbazole-9-yl)phenyl)anthracene (m-D15NCzDPA). When these novel ETMs were used in triplet–triplet fusion (TTF) fluorescent OLEDs, they exhibited superior performance compared to devices using the common ETMs TPBi and TmPyPB. In particular, devices based on m-S15NCzDPA and m-D15NCzDPA offered a maximum luminance (L_max) of 66 100 and 66 950 cd m⁻², maximum current efficiency (CE_max) of 17.40 and 17.20 cd A⁻¹, and maximum power efficiency (PE_max) of 12.20 and 11.70 lm W⁻¹ with a maximum external quantum efficiency (EQE_max) of 9.00% and 8.66%, respectively. More importantly, the device based on m-D15NCzDPA also achieved lower efficiency roll-offs at high luminance (roll-offs of 2.3% and 13.9% at 10 000 and 50 000 cd m⁻², respectively). This work demonstrated that a V-shaped layout of E_Ts strategy was beneficial for the construction of a series of high-performance ETMs.