Eco‐Designed Transparent Bacterial Cellulose Composites for Next‐Generation Opto‐Electronics

Sustainable, bio‐based alternatives to petrochemical substrates are essential for the fabrication of next‐generation optoelectronic devices. However, very few natural materials offer simultaneously high transparency, mechanical robustness, and functional versatility. Bacterial cellulose (BC) is mechanically exceptional but intrinsically opaque and hydrophilic, limiting its applicability in transparent optic and optoelectronics. Here, we report a single‐step, room‐temperature fabrication of a highly transparent BC composite via vacuum infiltration with plant‐derived soya resin (SGR). The resulting BC/SGR films achieves ∼89% optical transparency, 12% haze at 550 nm, and low reflectivity, while exhibiting enhanced tensile strength (up to 100 MPa), UV resistance, and hydrophobicity. Remarkably, its thermal conductivity is ∼50% lower than glass, and the substrate supports electrode deposition, enabling flexible, transparent, and functional optoelectronic devices. The applicability of this material is demonstrated by the fabrication of an electrochromic device, showing a transmittance modulation from 66% (bleached state) to 23% (colored state) at 550 nm. This green and scalable approach transforms bacterial cellulose into a high‐performance material, opening new pathways toward sustainable materials that merge ecological responsibility with advanced optoelectronic and optic functionality.