| In recent years, with the development of high conductive and optically transparentmaterials, optoelectronic devices have been attracting intense attention, especially for theflexible organic solar cells (OSC) and flexible organic light-emitting diodes (OLED), due totheir simple process and roll-to-roll production and low cost for fabrication. So far, Indium tinoxide (ITO) is currently the most popular material as the transparent electrode ofoptoelectronic devices. However, ITO has high mechanical brittleness and poor adhesion toorganic materials that makes it unsuitable for flexible electronic devices. Therefore, manynew transparent conductive materials have been investigated, including conducting polymers,carbon nanotubes, graphene and metal nanowires. Among those candidates, the conductivepolymer, poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)(PEDOT:PSS), is anoutstanding material, due to its transparency in the visible range, high mechanical flexibility,and excellent thermal stability. Presently, PEDOT:PSS has been widely used in organic solarcells, organic light-emitting diodes and super capacitors.Several methods have been reported to enhance the conductivity of PEDOT:PSS bymore than three orders of magnitude, including the addition of an organic compound, ionicliquid, anionic surfactant, or salt into PEDOT:PSS aqueous solution and the treatment ofethylene glycol and H2SO4on PEDOT:PSS film.In this paper we enhance the conductivity of PEDOT:PSS film up to1489S/cm throughthe treatment with Dodecyl benzenesulfonic acid (DBSA). The pristine PEDOT:PSS filmsfrom the Clevios PH1000aqueous solution had a conductivity of3S/cm. After the treatmentby DBSA at120℃for20minutes, the conductivity significantly increase to1489S/cm.This conductivity is lower than the highest conductivity3065S/cm as observed by Ouyang.This high conductive PEDOT:PSS film was treated by H2SO4. However that method withH2SO4was corrosive to the flexible plastic substrate PET. While the treatment with DBSAwas quite mild and it was suitable to treat PEDOT:PSS on the PET substrate.The mechanism of conductivity enhancement in PEDOT:PSS through DBSA treatmenthas been investigated by atomic force microscope (AFM), UV absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). The results showed the RMS roughness of thePEDOT:PSS films increased after the DBSA treatment, due to the conformational change ofthe polymer chains. The insulating PSS phase separated from the conductive PEDOT/PSSphase after the DBSA treatment, leading to clusters of PEDOT chains which enhance theinter-chain conductivity of PEDOT chains.We studied the effect of PEDOT:PSS films through DBSA treatment as an anode on theOLED. The OLED was fabricated by the facile and low cost solution process. The resultsindicated that the device performance of the OLED with PEDOT:PSS films as anode iscomparable to that of the control devices using ITO anode. The green flexbile OLED withPEDOT:PSS films as anode achieved a current efficiency of10.4cd/A at a luminance of100cd/m2, and maintained to13.0cd/A at1000cd/m2. While the OLED with ITO anode obtaineda current efficiency of6.8cd/A at luminance of100cd/m2, and10.3cd/A at1000cd/m2.Finally, We attempt to fabricate a flexible OSC using PEDOT:PSS films treated byDBSA as anode on the PET substrate. The performance of the flexible OSC was quite close tothe glass substrate device, which was also comparable to that of the devices with ITO anode.The the open circuit voltage (Voc) of flexible PEDOT:PSS-OSC was0.84V, which was alittle higher than the ITO-OSC with0.83V. However, the short-circuit current density (Isc) ofthe flexbile PEDOT:PSS-OSC was quite lower than the ITO-OSC, which was the mainlyreason leading to a lower photovoltaic energy conversion efficiency (PCE).The whole performance of PEDOT:PSS-OLED and PEDOT:PSS-OSC indicatePEDOT:PSS has a great potential in the application as flexible transparent anode. |
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