Photothermal Heat Spreading for Uniform Pixel Activation in NIR Laser-Driven Thermochromic Liquid Crystal Displays

Abstract

In this study, a pixelated full-color display based on a near-infrared (NIR) laser-driven thermochromic liquid crystal (TLC) was developed. TLCs exhibit temperature-dependent colors through Bragg reflection induced by variations in the helical pitch of their cholesteric structure. However, a Gaussian temperature distribution originating from the heating center causes color nonuniformity within the activated region (rainbow effect), while lateral heat diffusion to adjacent regions limits the realization of pixelated displays. To address these challenges, a pixelated multilayer structure (TLC/Graphite/Al/PDMS/Glass) was fabricated by integrating a graphite layer for NIR photothermal conversion with an Al thin film serving as an in-plane heat spreader. The pixel size and spacing were optimized to achieve RGB color separation, visual color distinguishability, and thermal isolation. As a result, red (∼27°C), green (∼29°C), and blue (∼31°C) colors were clearly generated without mutual interference, enabling the reproduction of complex full-color images. The proposed TLC-based photothermally driven display enables full-color image generation via non-contact optical actuation, eliminating the need for electrical wiring and demonstrating potential for next-generation form-factor display applications, including smart windows, anti-counterfeiting tags, and wearable devices.