Cellulose-Templated Stable Foldable Oriented Films with Polarized RGB Luminescence

Abstract

Solution processing in a vacuum-free system is highly advantageous because printing, coating, and roll-to-roll processes can be used for large-area and scalable manufacturing. However, producing a flat surface with high orientation is challenging. In addition, high folding stability is essential for building a basis for foldable devices. Herein, we present a valuable method to obtain oriented films of π-conjugated polymers, which we describe as a “Simple way of Orienting Films prepared by Templating cellulose,” abbreviated as SOFT. In this method, a glass or flexible substrate was uniaxially coated by a single-sweep process using a wet cloth containing a cellulose solution. A conjugated polymer solution, an OLED material, was deposited onto the cellulose film by spin coating, followed by thermal annealing. A uniaxially oriented film was obtained with orientation factors up to 0.9, and its polarized fluorescence was verified for red/green/blue colors. The oriented films were stable at various positions and showed no degradation of orientation factors after folding 100–500 times at a folding angle of 320°. The homogeneous area and surface roughness of the films were approximately 2 × 3 cm2 and 50 nm, respectively, with an orientation reproducibility of ∼96%. A high tensile strength of 30 MPa was measured on the oriented films. The orientation mechanism was attributed to the alignment of the backbone structure of the conjugated polymers along the surface anisotropy of a uniaxially coated cellulose film.