Ultrathin Grid-Structured Crystalline Silicon Films with Through-Hole Arrays for Flexible and Transparent Wearable Optoelectronics

Ultrathin crystalline silicon (c-Si) is a promising material for wearable electronics. However, its intrinsic brittleness and limited optical transparency hinder its broader application in flexible devices. This study introduces a novel grid-structured c-Si (GSC-Si) film by etching patterned circular through-holes into ultrathin c-Si. This design imparts lightweight, mechanical flexibility, and optical transparency to the c-Si film. The fabricated GSC-Si film remains structurally intact under continuous bending with a radius of 0.2 mm while achieving a visible-light transparency of 75%. A transparent and flexible photodetector (TFPD) developed on this film exhibits self-powered photodetection across the ultraviolet (UV) to near-infrared (NIR) spectrum. When it is conformally mounted on a finger as a photoplethysmography (PPG) biosensor, the TFPD successfully captures subdermal pulse signals. The outstanding performance and design methodology of this GSC-Si film provide new insights for the development of Si-based flexible wearable electronics.