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

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 & pi;-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 x 10-4 cm2 V-1 s-1 and 2.0 x 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 (EQEmax) 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. A blue emitter with effective & pi;-stacking between acceptors is developed, which improves and balances carrier mobilities, obtaining higher device efficiency.

Automated summary

In this study, two donor-acceptor (D-A) type blue emitters with bipolar transmission were synthesized, and their hybridized local and charge-transfer (HLCT) excited state was demonstrated to achieve high electron mobility. The single crystal results showed that tPPIDPO exhibited effective acceptor-acceptor π-stacking and highly ordered molecular arrangement, leading to higher electron and more balanced carrier mobilities. The non-doped blue OLED based on tPPIDPO achieved a maximum external quantum efficiency (EQEmax) of approximately 7.0%, which is among the highest reported for D-A type blue fluorescence emitters with HLCT using DPO as the acceptor. The development of a blue emitter with effective acceptor-acceptor π-stacking improves and balances carrier mobilities, resulting in higher device efficiency.