Novel Liquid Crystal Displays Based on Highly Polarized Photoluminescent Polymer Films

Abstract

Since the early 90s's, much research has focused on the photoluminescence (PL) and electroluminescence (EL) properties of conjugated polymers, because of their potential application as emitting layer in EL devices. The introduction of uniaxial molecular orientation into films of luminescent polymers was naturally found to yield structures that emit polarized light. Rather surprisingly, the photoluminescence properties of oriented, conjugated polymers have attracted substantially less attention, especially from an application point of view. In this paper we report the fabrication of highly-polarized photoluminescent polymer films based on poly(2,5-dialkoxy-{tip}-phenyleneethynylene)s (PPE), and their use in a new family of liquid crystal displays (LCDs). As one relevant example, a back-lit twisted-nematic configuration of an LCD was built, in which one of the absorbing polarizers was replaced by a polarized PL film, characterized by a dichroic ratio in excess of 70. Such devices can exhibit a substantial improvement in brightness, contrast and viewing angle, since the polarized photoluminescent films can combine two separate features, i.e. the functions of a polarizer and an efficient color filter.