Original ResearchVol. 32, Issue 12 • pp. 100-112DOI: 10.1088/1674-4926/25120050• Jan 15, 2025
Authors: Tongqing Zhou, Jianmin Li, Shujuan Liu, Qiang Zhao
In an era dominated by visual information, the display interface serves as a critical gateway between the human and digital worlds. The relentless pursuit of visual immersion has driven display technology from cinema screens to smartphones and now to virtual and augmented reality (VR/AR) headsets, progressively moving closer to the human eye. This evolution places unprecedented demands on pixel density, power efficiency, and form factor, pushing up against fundamental physical and physiological limits. The core challenge lies in creating displays that, when viewed at close proximity, offer a seamless, high-fidelity visual experience indistinguishable from reality—a goal often conceptualized as the 'retina display', where the pixel density matches or exceeds the resolving power of the human eye. However, as pixel sizes shrink into the sub-micrometer regime, conventional emissive technologies like organic light-emitting diodes (OLEDs) and micro-light-emitting diodes (micro-LEDs) face insurmountable hurdles: diminished emission intensity, non-uniformity, severe colour cross-talk, and rapidly increasing fabrication complexity. Even the most advanced micro-LED demonstrations struggle to achieve the required pixel densities across large fields of view without significant performance trade-offs. Conversely, reflective displays, or electronic paper (E-paper), which leverage ambient light for visibility, inherently avoid the luminosity and efficiency issues of emissive displays. Their optical contrast is governed by material properties at the nanoscale, remaining theoretically unaffected by pixel size reduction. Yet, established reflective technologies, such as electrophoretic displays (e.g., those in e-readers), have been hamstrung by slow refresh rates (seconds), limited colour gamuts, and resolutions typically below 1000 pixels per inch (PPI), confining them largely to static text and image applications. While optical metasurfaces have demonstrated astonishing static resolutions exceeding 10 000 PPI, they have largely remained just that—static—lacking the dynamic tunability essential for video and interactive content. Previous attempts to create dynamic reflective displays using hybrid nanomaterials have improved colour and speed but failed to break the micron-scale pixel barrier, leaving the holy grail of a high-resolution, video-rate, low-power reflective display tantalizingly out of reach. Now, writing in Nature, Santosa et al. achieve a retina E-paper that not only surmounts these historical limitations but also redefines the possibilities for ultra-high-resolution displays, based on traditional electrochromic (EC) technology. By demonstrating electrically tunable pixels down to ~560 nm in size (>25 000 PPI), full-colour video capability (>25 Hz), high reflectance (~80%), and remarkably low energy consumption (0.5–1.7 mW∙cm–2), they present a paradigm shift from light-emitting to intelligently light-modulating displays at the nanoscale.
