Host-Free Deep-Blue Organic Light-Emitting Transistors Based on a Novel Fluorescent Emitter.

Organic light-emitting transistors (OLETs), with the capability of simultaneously functioning as a light-emitting stack and a thin-film transistor, have received considerable attention for potential applications in active-matrix flat-panel displays. Here, we demonstrate host-free deep-blue OLETs based on a novel small-molecule fluorescent emitter, 10,10'-bis(4-(1-phenyl-1H-benzo[]imidazol-2-yl)phenyl)-10H,10'H-9,9'-spirobi[acridine] (SPA-PBI), and a high-k dielectric, cross-linked poly(vinyl alcohol) (PVA) polymer. The deep-blue OLETs based on 2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) as an electron-transport layer showed an extraordinarily high hole mobility of 4.6 cm V s, a brightness of 570 cd m under a low gate and source-drain voltages of -24 V, and an external quantum efficiency (EQE) of 0.87% at 100 cd m. Besides, an electroluminescence peak was observed to be at 432 nm and the corresponding CIE coordinates were as deep as (0.16, 0.08). By replacing TPBi with TmPyPB as the electron-transport layer (ETL), the electron transport and hole blocking capability were greatly improved, which led to ∼60% enhancement of the EQE (1.39% at 100 cd m). These results suggest that using a highly twisted double-donor-acceptor emitter with rationally optimized charge injection could lead to highly efficient deep-blue OLETs.