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[d]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 cm² V^-1 s^-1, a brightness of 570 cd m^-2 under a low gate and source-drain voltages of -24 V, and an external quantum efficiency (EQE) of 0.87% at 100 cd m^-2. 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^-2). 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.