Abstract
Inserting a hole-buffer layer is an effective way to enhance emission efficiency of electroluminescence devices. We have successfully synthesized a new hole-buffer material PSB composed of pyrene, Schiff base and trihydroxy tert-butyl groups by the Suzuki-coupling reaction. The HOMO and LUMO lev-els were -6.33 eV and -2.55 eV, respectively, as estimated from cyclic volt-ammograms. In addition, homogeneous films (rms roughness ~2 nm) were readily obtained by spin-coating process. Multilayer polymer light-emitting diodes, ITO/PEDOT:PSS/PSB/SY/LiF/Al, have been fabricated using PSB as hole-buffer layer (HBL). Inserting PSB as HBL significantly enhances the per-formance (maximum luminance: 26,439 cd/m2, maximum current efficiency: 7.03 cd/A), compared with the one without PSB (9802 cd/m2, 2.43 cd/A). It is also superior to the device with conventional BCP as hole-blocking layer (ITO/PEDOT:PSS/SY/BCP/LiF/Al: 15,496 cd/m2, 5.56 cd/A). Current results strongly indicate that the PSB is a potential hole-buffer material for electrolu-minescent devices.
Highlights
Organic light-emitting diodes (OLEDs) and polymer light-emitting diodes (PLEDs) have attracted considerable attention from both academic and industrial points of view due to promising applications in flat panel displays and solid-state lightings [1] [2] [3]
We have successfully synthesized a new compound PSB composed of pyrene core linked with trihydroxy tert-butyl groups through imine moiety by the Suzuki-coupling reaction and applied as hole-buffer layer in multilayer PLEDs
The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of PSB were −6.33 and −2.55 eV respectively, estimated from onset oxidation and reduction potentials determined by cyclic voltammetry
Summary
Organic light-emitting diodes (OLEDs) and polymer light-emitting diodes (PLEDs) have attracted considerable attention from both academic and industrial points of view due to promising applications in flat panel displays and solid-state lightings [1] [2] [3]. Hole mobility in most organic materials is higher than electron mobility [6]; the injection rate of holes for most OLED/PLED devices is greater than that of electrons. This leads to imbalanced carriers and reduced device efficiency. Carriers balance can be improved by multilayer device structure, i.e., inserting electron injection and transport layers between emission layer and the cathode [7] [8] In this way, the injection and transport of electrons are raised to a level comparable to those of holes, resulting in more balanced carriers. The formation of excitons too near the interface usually leads to diminished color purity and emission efficiency [13]
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