Influence of methyl red as a dopant on the electrical properties and device performance of liquid crystals

The ionic effect in nematic liquid-crystal (LC) cells containing the azo dye methyl red was investigated by means of dielectric spectroscopy, measurements of voltage holding ratio (VHR) and ultraviolet/visible absorption spectroscopy. The experimental results indicated that incorporating a minute amount of the methyl red (< 0.03 wt%) in the LC host leads to the suppression of the ionic effect caused by impurity ions. Practically, the doped LC cells with a dye content of 0.02 wt% showed improved VHR and promoted lifetime by 15% and 180%, respectively, in virtually no expense of the optical transmittance.