Optoelectronic characteristics of polymer light emitting diodes with poly(2-methoxy-5-(2′ethyl-hexoxy)-1,4-phenylene-vinylene) and hydrogenated amorphous silicon alloy heterointerfaces

Abstract

In order to investigate the feasibility of combining polymer and inorganic films for light-emitting diode (LED) fabrication, the inorganic p-amorphous-Si:H/n-amorphous-SiCGe:H layer was employed as hole/electron injection layer (HIL/EIL) in the poly(2-methoxy-5-(2′ ethylhexoxy)-1,4-phenylene-vinylene) polymer LEDs (PLEDs). In contrast to the PLED without any amorphous HIL/EIL, which had an electroluminescence (EL) threshold voltage (Vth) of 10 V and a brightness of 1231 cd/m2 at an injected current density (J)=0.6 A/cm2, the EL Vth could be reduced to 6.9 V for PLED with a 6 nm p-a-Si:H HIL only, also, the brightness could be enhanced to 6450 cd/m2 (at J=0.3 A/cm2 only) for PLED with both p-amorphous-Si:H HIL and n-a-SiCGe:H EIL.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

“…A combination of ultrathin layers of electron transporting aluminum tris(8-hydroxyquinolate) (Alq 3 ) and lithium fluoride gives even better results (2.5% efficiency) . Composite electrodes containing a thin layer of calcium or barium between the polymer and aluminum also enhance device performance, , as does the introduction of an electron-injecting layer. ,,,,,− The use of polyaniline (PANI) or composite ITO/PANI or PANI−camphorsulfonic acid (CSA) electrodes is reported to reduce the driving voltage and to increase the quantum efficiency and lifetimes of devices based on MEH-PPV as emissive layer by over 30%. − Similar effects have also been reported from use of ITO coated with a PEDOT:PSS or polythiophene layer, or with self-assembled layers of a silazane or polyelectrolyte multilayers as anode. MacDiarmid and co-workers have shown that introduction of ionic dopants by treatment of the MEH-PPV layer with iodine leads to a drop in turn-on voltage and a 10-fold increase in efficiency. − The use of a doped emeraldine base polyaniline (EB-PANi) − or poly(styrene sulfonic acid) layer has similar effects.…”