Study On Doping Polymer Light-Emitting Electrochemical Cells

A polymer light-emitting electrochemical cell( LEC ) offers an alternative approach to achieving electroluminescence (EL) from conjugated polymers. Different from a polymer light-emitting diode(PLED),the emitting layer of LEC contains ionic conductor such as poly(ethylene oxide) (PEO) mixed with lithium salt. In these solid-state LECs, the conjugated polymers are p-doped on the anode side and n-doped on the cathode side and a light-emitting p-n junction is formed between the p-doped and n-doped regions. The LEC was shown to operate in both forward and reverse bias, effectively independent of the electrode workfunction. Compared with PLED, LEC has the advantages of low turn on voltage and high quantum efficiency of its electro luminescence.In this work, a traditional film LEC device is fabricated and a method to build thick-film LEC is suggested. By mixing metallic particles into an electrolyte /electroluminescent composite polymer film, light-emitting p-n junctions are formed in situ by electrochemical p- and n-doping randomly. This device offers a substructure to achieve organic photovoltaic device with high open circuit.The luminescence of LEC based on emitting material doped with different dye has been researched. Doping organic dye into the luminescent materials of LEC may change the wavelength of device and fabricate LECs with various wavelengths, even the white emitting LECs. Red dye DCJTB is doped into MEH-PPV then a LEC device with a sandwich structure of ITO/MEH-PPV+PEO+LiCF3SO3+DCJTB/Al is fabricated. EL peak wavelength of the LEC devices ranges from 570 nm to 650 nm continuously, depending on the doping concentration of DCJTB. In the PL spectra with the excitation wavelength of MEH-PPV, it is observed that the emission from MEH-PPV decrease and DCJTB increase with the rise of the doped DCJTB mass concentration. This indicates that energy transfer occur from MEH-PPV to DCJTB. The redshift of DCJTB's emission cause by its concentration increase is another factor for the phenomena. Using green emitting material Poly[(BEHP-PPV)-co-(MEH-PPV)] as the luminescent materials of LEC, a green emitting LEC is fabricated and similar phenomenon is observed when the DCJTB was doped in to the host material in the LEC.