Showing papers by "Yang Yang published in 1996"

Polymer Light-Emitting Electrochemical Cells: In Situ Formation of a Light-Emitting p-n Junction.

Abstract: Solid-state polymer light-emitting electrochemical cells have been fabricated using thin films of blends of poly(1,4-phenylenevinylene) and poly(ethylene oxide) complexed with lithium trifluoromethanesulfonate. The cells contain three layers: the polymer film (as the emissive layer) and indium-tin oxide and aluminum films as the two contact electrodes. When externally biased, the conjugated polymers are p-doped and n-doped on opposite sides of the polymer layer, and a light-emitting p-n junction is formed in between. The admixed polymer electrolyte provides the counterions and the ionic conductivity necessary for doping. The p-n junction is dynamic and reversible, with an internal built-in potential close to the band gap of the redox-active conjugated polymer (2.4 eV for PPV). Green light emitted from the p-n junction was observed with a turn-on voltage of about 2.4 V. The devices reached 8 cd/m(2) at 3 V and 100 cd/m(2) at 4 V, with an external quantum efficiency of 0.3-0.4% photons/electron. The response speed of these cells was around 1 s, depending on the diffusion of ions. Once the light-emitting junction had been formed, the subsequent operation had fast response (microsecond scale or faster) and was no longer diffusion-controlled.

Voltage controlled two color light‐emitting electrochemical cells

Abstract: A polymer light‐emitting electrochemical cell (LEC) is a bipolar p‐n junction device; when biased, a dynamic light‐emitting p‐n junction is created. In this letter, we report a two color LEC in which the color can be switched by simply reversing the bias voltage. The two color LEC consists of a polymer bilayer structure sandwiched between two electrodes. In this study, the polymer bilayer consists of a poly(1,4‐phenylene vinylene) (PPV) layer and a poly[2‐methoxy‐5‐ (2′‐ethylhexyloxy)‐1,4‐phenylene vinylene] (MEH‐PPV) layer. When biased at one polarity, the voltage induced p‐n junction is completely inside the PPV layer, and the LEC emits the green light of PPV. When biased at the opposite polarity, the p‐n junction is completely inside the MEH‐PPV layer, and the LEC emits the orange light characteristic of MEH‐PPV.

Plastic retina: image enhancement using polymer grid triode arrays

Abstract: An array of polymer grid triodes (PGTs) connected through a common grid functions as a 'plastic retina' which provides local contrast gain control for image enhancement. This device, made from layers of conducting polymers, functions as an active resistive network that performs center-surround filtering. The PGT array with common grid is a continuous analog of the discrete approach of Mead, with a variety of fabrication advantages and with a significant saving of 'real estate' within the unit cell of each pixel.

Efficient green-blue polymer light emitting electrochemical cells

Abstract: Summary form only given. Efficient green-blue color light-emitting electrochemical cells (LECs) using ITO and aluminum as electrodes have been demonstrated. Devices with 4% external quantum efficiency and higher than 10 lumens/watt power efficiency have been demonstrated; the brightness is /spl sim/190 cd/m/sup 2/ at 3.1 volts and increases to /spl sim/1000 cd/m2 at 3.5 volts. To our knowledge, this is the best performance reported for polymer and organic light-emitting devices. These polymer LECs show competitive device performance even when compared to the latest gallium nitride light-emitting diodes.