Electrolyte-Gated Red, Green, and Blue Organic Light-Emitting Diodes

Abstract

We report vertical electrolyte-gated red, green, and blue phosphorescent small-molecule organic light-emitting diodes (OLED), in which light emission was modified by tuning the electron injection via electrochemical doping of the electron injection layer 4,4-bis(N-carbazolyl)-1,1-biphenyl (CBP) under the assistance of a polymer electrolyte. These devices comprise an electrolyte capacitor on the top of a conventional OLED, with the interfacial contact between the electrolyte and electron injection layer CBP of OLEDs achieved through a porous cathode. These phosphorescent OLEDs exhibit the tunable luminance between 0.1 and 10 000 cd m, controlled by an applied bias at the gate electrode. This simple device architecture with gate-modulated luminance provides an innovative way for full-color OLED displays.

Gate Tunable Organic Light Emitting Diodes: Principles and Prospects

“…Like the observed current density profiles in transfer curves, the output current densities also show slight changes with various gate potentials. The optical spectrum of each R, G and B device was also measured as shown in Figure I–5 K and are seen to remain the same at different gate potentials …”

“…For marketing adoption, gate‐tunable electron‐injection based OLEDs were also fabricated with red, green and blue phosphorescent small molecules . Figure A illustrates a schematic structure of gated OLEDs.…”

“…From bottom to top, the OLED structure consists of an ITO anode, a hole injection layer PEDOT:PSS, a hole transport layer (4,4‐cyclohexylidenebis [N,N‐bis (4‐methylphenyl) benzenamine] (TAPC)) of 40 nm, a light‐emission layer (4,4‐bis (N‐carbazolyl)‐1,1‐biphenyl (CBP)) of 40 nm, and a porous aluminum (Al) cathode of 25 nm. The portion of the CBP acting as the EML (10 nm) is doped with three different phosphorescent guests, the red guest bis (1‐phenylisoquinoline)‐(acetylacetonate) iridium (III), the green guest (tris [2‐(p ‐tolyl) pyridine] iridium (III)), and the blue guest bis [2‐(4, 6‐difluorophenyl) pyridinato‐C2,N](picolinato) iridium (III), while the remaining 30 nm of undoped CBP acts as the electron transport layers . All materials’ structures are shown in Figure B.…”

Vertical Organic Field‐Effect Transistors

“…The permeable Al cathode electrode is crucial and PE can assist reversible electrochemical oxidation or reduction through the source electrodes by applying gate voltage. [101] The PMMA takes up a large portion of electrolyte layer and gate current is in principle depended on the proportion of PMMA. Although the current-density on/off ratio is relatively small in such devices, a large brightness of 4400 cd m −2 together with an external quantum efficiency of 2.3% has still been achieved at V DD = 7 V (Figure 9c).…”

“…[100] Electrolyte-gated OLETs based on red, green, and blue phosphorescent small-molecule are further constructed where the electrolyte layer is composed of a solidifier [poly(methyl methacrylete) PMMA], an ion conductor [poly(ethylene oxide) (PEO)], and a salt (CF 3 SO 3 Li) in a weight ratio of 1:5:10. [101] The PMMA takes up a large portion of electrolyte layer and gate current is in principle depended on the proportion of PMMA. Although this kind of VOLETs demonstrates high luminance and large optical contrast with luminance of 0.1 cd m −2 at negative gate voltage to 10 000 cd m −2 at positive gate voltage for green colors which are sufficient for display applications, the small current density on/off ratio leads to large power consumption at off-state.…”