Ultra‐Thin GaAs Single‐Junction Solar Cells for Self‐Powered Skin‐Compatible Electrocardiogram Sensors

Abstract GaAs thin‐film solar cells have high efficiency, reliability, and operational stability, making them a promising solution for self‐powered skin‐conformal biosensors. However, inherent device thickness limits suitability for such applications, making them uncomfortable and unreliable in flexural environments. Therefore, reducing the flexural rigidity becomes crucial for integration with skin‐compatible electronic devices. Herein, this study demonstrated a novel one‐step surface modification bonding methodology, allowing a streamlined transfer process of ultra‐thin (2.3 µm thick) GaAs solar cells on flexible polymer substrates. This reproducible technique enables strong bonding between dissimilar materials (GaAs‐polydimethylsiloxane, PDMS) without high external pressures and temperatures. The fabricated solar cell showed exceptional performance with an open‐circuit voltage of 1.018 V, short‐circuit current density of 20.641 mA cm −2 , fill factor of 79.83%, and power conversion efficiency of 16.77%. To prove the concept, the solar cell is integrated with a skin‐compatible organic electrochemical transistor (OECT). Competitive electrical outputs of GaAs solar cells enabled high current levels of OECT under subtle light intensities lower than 50 mW cm −2 , which demonstrates a self‐powered electrocardiogram sensor with low noise (signal‐to‐noise ratio of 32.68 dB). Overall, this study presents a promising solution for the development of free‐form and comfortable device structures that can continuously power wearable devices and biosensors.