Transmission Enhancement in Nanoparticle-induced Vertical Alignment Liquid Crystal Cell by Using Highly Conductive Pedot:Pss as Transparent Electrode
Szu-Hua Chen1*, Tsu-Ruey Chou1, Yen-Te Chiang2, Chih-Yu Chao1,2
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Graduate Institute of Applied Physics, National Taiwan University, Taipei, Taiwan
* presenting author:Szu Hua Chen,
In recent years, nanoparticle-doped liquid crystals (LCs) have attracted many investigations because of the potential development in promoting the electro-optical characteristics of LCs, such as low driving voltage, fast response time, memory effects and frequency modulation. In particular, the spontaneously vertical alignment (VA) induced by dispersing nanoparticles into LCs becomes an attractive alignment technique.
The nanoparticle-induced VA LCs arise from the adsorption of the nanoparticles on both inner surfaces of the LC cell. Since this simple process does not require typically high curing temperature used in the manufacturing of conventional alignment layer, this method is very suitable for low-temperature or flexible display fabrication process. However, a nanoparticles-filled VA cell without the conventional rubbed alignment layer would form the schlieren texture (inset of Figure 1a), suggesting that the directors of LC molecules were not uniformly orientated under applied voltage. This is due to the absence of the preferred azimuthal alignment produced by the rubbing process, which results in significant reduction in the transmission and the contrast ratio of the LC cell.
In this work, high transmittance VA LC cells constructed from highly conductive PEDOT:PSS films with addition of poly oligomeric silsesquioxane (POSS) nanoparticles were achieved. The highly conductive PEDOT:PSS films not only could offer the advantage of excellent mechanical flexibility, but also could be treated with rubbing process to generate a preferred azimuthal direction to LC molecules under applied voltage. Therefore, no disclination lines were observed (inset of Figure 1a), and the contrast ratio of the cell fabricated by PEDOT:PSS and POSS is 2.3 times larger than that of the cell constructed by ITO and POSS. Moreover, the electro-optical properties of the VA LC cell using PEDOT:PSS and POSS are similar to those of the conventional VA LC cell composed of ITO and polyimide (PI) alignment layer. Here our work shows the potential of flexible LC devices with high transmittance by using POSS-induced VA on rubbed PEDOT:PSS films for ITO-free LC displays.

Keywords: Liquid Crystals, nanoparticles, PEDOT:PSS, ITO free