Poly(3,4-ethylenedioxythiophene):sulfonated poly(diphenylacetylene) complex as a hole injection material in organic ligh
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Research Letter
Poly(3,4-ethylenedioxythiophene):sulfonated poly(diphenylacetylene) complex as a hole injection material in organic light-emitting diodes Jung Jae Kim† and Jin Chul Yang†, Major in Polymer Science & Engineering, School of Applied Chemical Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Republic of Korea Keunbyung Yoon, Giseop Kwak, and Jin Young Park, Major in Polymer Science & Engineering, School of Applied Chemical Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Republic of Korea; Department of Polymer Science & Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Republic of Korea Address all correspondence to Giseop Kwak, Jin Young Park at [email protected], [email protected] (Received 9 June 2017; accepted 20 July 2017)
Abstract New ionic conjugated polyelectrolyte complex films based on poly(3,4-ethylenedioxythiophene):sulfonated poly(diphenylacetylene) (PEDOT: SPDPA) are electrochemically formed on indium thin oxide substrates using a potentiostatic method, and their physical properties are evaluated using various analytical tools. Depending on a constant applied voltage, the surface morphological features and electrochemically doped states are different due to the conformational structure related to the oxidation state in the PEDOT growth process and concomitant SPDPA doping state in the films. For the purpose of use as a hole injection layer in organic light-emitting diodes, a well-known configuration (ITP/PEDOT:SPDPA/TPD/Alq3/LiF/Al) is adopted to investigate the optoelectronic properties.
Introduction Conjugated polymers have attracted great interest in the field of optoelectronic devices such as organic solar cells and organic light-emitting diodes (OLEDs) owing to easier fabrication, higher flexibility, and lower manufacturing cost. In general, polyaniline and polythiophene derivatives have been widely used as hole transport layers (HTLs) in solar cells[1] or hole injection layers (HILs) in OLEDs.[2] Poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives have also been studied extensively and used in many applications, such as tissue engineering, batteries, sensors, and corrosion protection.[3] Particularly, in the cases using as HIL or HTL materials, PEDOT is mostly used as polyelectrolyte blend systems [e.g., PEDOT:poly(styrene sulfonic acid) (PSS)].[4] Such blends are considerably useful because the energy barrier at the organic–organic interface can be adjusted by effectively controlling hole injection and transport from an active layer or anode. Furthermore, PEDOT:PSS can be synthesized either chemically or electrochemically,[5] and has been used for a long time as a HIL in OLEDs owing to its high transparency in the visible region, conductivity, and thermal stability.[6] For the optoelectronics applications, various methods have been developed to enhance the electrical conductivity of PEDOT:PSS, including solvent treatment,[7] pH adjustment,[8] electrochemical doping,[9] and use of composite l
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