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Author: search.filters.author.Keawprajak, Anusit

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    Effects of tetramethylene sulfone solvent additives on conductivity of PEDOT:PSS film and performance of polymer photovoltaic cells
    (2013-01-01)
    Keawprajak, Anusit
    ;
    Koetniyom, Wantana
    ;
    Piyakulawat, Phimwipha
    ;
    Jiramitmongkon, Kanpitcha
    ;
    Pratontep, Sirapat
    A solvent additive in PEDOT:PSS solution is one of many methods to improve the conductivity of the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. We explore a new type of the solvent additive, namely tetramethylene sulfone (TMS), for the fabrication of the PEDOT:PSS conductive layer in the ITO/PEDOT:PSS/P3HT:PCBM/TiO<inf>x</inf>/Al polymer photovoltaic cells, in comparison to a more common dimethyl sulfoxide (DMSO) solvent additive. At optimal conditions, the TMS additive at 10 wt.% has been found to enhance the conductivity of pristine PEDOT:PSS films from 0.04 S/cm up to approximately 189 S/cm, compared with the highest conductivity for the case of the DMSO additive at 15 wt.% of 117 S/cm. Possible mechanisms of this conductivity enhancement, relating to the polymer conformation and the film morphology, have been investigated by Raman spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy. The performance of the polymer photovoltaic cells fabricated with the solvent additives PEDOT:PSS films follows a similar trend to the conductivity of the films as a function of the additive concentration. The additives mainly lead to greater short circuit current density (J<inf>sc</inf>) of the photovoltaic cells. The highest power conversion efficiency (PCE) of 2.24% of the device has been obtained with the 10 wt.% TMS additive of, compared to the PCE of 1.48% for the standard device without solvent additive. © 2012 Elsevier B.V. All rights reserved.
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    Blue emission mechanism of NPB/ZnSe hybrid structure
    (2007-08-28)
    Kayunkid, Navaphun
    ;
    Keawprajak, Anusit
    ;
    Jaruwanawat, Anuchit
    ;
    Nukeaw, Jiti
    The electrical and optical properties of organic-inorganic hybrid light emitting diodes (HLED) have been investigated. The HLED is consisted of organic material N,N'-di(naphthalene-1-yl)-N,N'- diphenyl-benzidine (NPB) as a hole transport layer and inorganic material zinc selenide (ZnSe) as an electron transport layer and emitting layer as well. The electrical and optical properties have been characterized by current-voltage measurement and electroluminescence (EL) spectroscopy, respectively. The current of HLED decreases with increasing ZnSc thickness, while the threshold voltage increases. The EL spectrum exhibits two peaks at 457 nm and 500 nm, due to electron-hole recombination from energy gap of ZnSe and recombination from defect states in ZnSe layer, respectively. The emission mechanism is described by electric field in organic and inorganic layers. © 2007 IEEE.
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    Growth and characterization of novel optoelectronic materials. Based on II-VI inorganic/organic heterostructures
    (2006-01-01)
    Pecharapa, Wisanu
    ;
    Keawprajak, Anusit
    ;
    Kayunkid, Nawapun
    ;
    Rahong, Sakon
    ;
    Yindeesuk, Witoon
    Novel optoelectronic materials based on II-VI inorganic/organic low-dimensional heterostructure were successfully grown by electron beam evaporator. The structures were based on ZnSe, tris(8-hydroxyquinoline) aluminum (Alq<inf>3</inf>) and N,N'-bis(3-methylphenyl)-N,N'-diphenyl-benzidine (TPD). The surface morphology of the structures was investigated by atomic force microscopy and field emission scanning electron microscope. The optical and electronic properties were examined by photoluminescence, photocurrent and electroreflectance spectroscopy. Photoluminescence spectra of the ZnSe/Alq <inf>3</inf>/ZnSe structure attributed to the change of exciton energy as a result of quantum confinement showed the formation of single quantum well structure. The luminescence color can be varied by changing the thickness of the Alq<inf>3</inf> layer. The other heterostructure of ZnSe/Alq<inf>3</inf>/TPD was grown on silicon substrate. The wavelength response of this structure shown by photocurrent signal ranged from 450 nm to 1100 nm. Electroreflectance features due to optical transition energy of the single quantum well of this structure were also observed. Under applied voltage, electroreflectance signals showed significant shift due to the quantum confined Stark effect.