유기발광다이오드용 고전도성 고분자 PEDOT:PSS 투명전극의 최적화에 관한 연구

Abstract

The development of high performance electrodes is of great importance for efficient, low-cost organic optoelectronic devices such as organic solar cells and organic light-emitting diodes (OLEDs). The commonly used indium tin oxide (ITO) as a bottom electrode remarkably increases device costs due to limited indium supply and the inherent brittleness of the material, which hinders the applications in flexible devices. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a conductive polymer, is in particular regarded as a promising electrode material due to its high transmittance and conductivity, and mechanical flexibility. It is investigated that an addition of polar organic compounds with a high boiling point or various solvent post-treatment methods greatly increases the conductivity of PEDOT:PSS films. In this work, we demonstrate high conductivity PEDOT:PSS films with 2-ethoxyethanol (2EE) which greatly improves the conductivity of PEDOT:PSS films up to 761.7 S/cm. Additionally, a solvent post-treatment performed for the PEDOT:PSS films further enhances the conductivity of 2EE doped PEDOT:PSS films up to 940.9 S/cm. The sheet resistance of the post-treated PEDOT:PSS film greatly decreases from 162.3 ohm/sq to 116.2 ohm/sq. The optimized PEDOT:PSS shows a low transmittance of 82.3 % with a low sheet resistance of 116.2 ohm/sq, which values are sufficient for the transparent electrode in OLEDs. The optimized PEDOT:PSS films with 2EE are adopted as a bottom electrode for organic light-emitting diodes and show excellent device performance. The efficiency of the OLED with optimized PEDOT:PSS films is comparable to that of the reference OLED based on ITO electrodes. The results indicate that the optimized PEDOT:PSS films with 2EE can be a promising transparent electrode for low-cost, flexible ITO-free OLEDs.