Calcium Alginate as an Active Device Component for Light-Triggered Degradation of 2D MoS₂-Based Transient Electronics

Transient electronics technology has enabled the programmed disintegration of functional devices, paving the way for environmentally sustainable management of electronic wastes as well as facilitating the exploration of novel device concepts. While a variety of inorganic and/or organic materials have been employed as media to introduce transient characteristics in electronic devices, they have been mainly limited to function as passive device components. Herein, we report that calcium (Ca) alginate, a natural biopolymer, exhibits multifunctionalities of introducing light-triggered transient characteristics as well as constituting active components in electronic devices integrated with two-dimensional (2D) molybdenum disulfide (MoS 2 ) layers. Ca 2+ ions-based alginate electrolyte films are prepared through hydrolysis reactions and are subsequently incorporated with riboflavin, a natural photosensitizer, for the light-driven dissolution of 2D MoS 2 layers. The alginate films exhibit strain-sensitive triboelectricity, confirming the presence of abundant mobile Ca 2+ ions, which enables them to be active components of 2D MoS 2 field-effect transistors (FETs) functioning as electrolyte top-gates. The alginate-integrated 2D MoS 2 FETs display intriguing transient characteristics of spontaneous degradation upon ultraviolet-to-visible light illumination as well as water exposure. Such transient characteristics are demonstrated even in ambient conditions with natural sunlight, highlighting the versatility of the developed approach. This study emphasizes a relatively unexplored aspect of combining naturally abundant polymers with emerging near atom-thickness semiconductors toward realizing unconventional and transformative device functionalities.