An efficient blue electro-fluorescence material with high electron and balanced carrier mobilities based on effective π-stacking between acceptors

Abstract

High and balanced carrier mobilities are indispensable for highly efficient blue organic light-emitting diodes (OLEDs), and especially how to improve electron mobility becomes a key problem. Herein, two donor–acceptor (D–A) type blue emitters (tPPIDPO and tPCZDPO) with bipolar transmission were synthesized. Both experimental and calculation methods demonstrate that these molecules exhibit the hybridized local and charge-transfer (HLCT) excited state and achieve high electron mobility due to the addition of the acceptor 2,5-diphenyl-1,3,4-oxadiazole (DPO). More importantly, the single crystal results indicate that tPPIDPO not only exhibits effective π-stacking in a face-to-face arrangement between acceptors (A–A), but also exhibits a highly ordered molecular arrangement, resulting in higher electron and more balanced carrier mobilities. The electron and hole mobilities of tPPIDPO are as high as 1.3 × 10⁻⁴ cm² V⁻¹ s⁻¹ and 2.0 × 10⁻⁵ cm² V⁻¹ s⁻¹, respectively. Benefiting from the above facts, a non-doped blue OLED of tPPIDPO obtained the maximum external quantum efficiency (EQE_max) approaching 7.0%. Its device performance is at the highest level among the reported D–A type blue fluorescence emitters with HLCT using DPO as the acceptor.