Boosting carrier transfer at flexible schottky junctions with moisture: A strategy for high-performance wearable direct-current nanogenerators

Highlights: • Moisture-induced electric field was utilized to boost carrier transfer at flexible DC Schottky junctions. • The flexible DC Schottky nanogenerator comprising an asymmetric graphene oxide layer and an aluminum is designed and prepared. • The Nanogenerators output a current density of 81.06 A m⁻², power density of 24.08 W m⁻², and conversion efficiency of 2.29%. • Self-powered sensors based on this nanogenerator can simultaneously detect sweat levels and the respiratory system of humans. The development of high-performance direct-current (DC) nanogenerators with good flexibility in wearable devices has always been a major challenge. A potential solution is developing the flexible Schottky nanogenerators to output DC power by introducing Schottky interfaces between metals and flexible semiconductors to directionally transfer the mechanically excited carriers. However, the DC output of existing flexible Schottky nanogenerators is limited by the moderate carrier transfer at the interface. Herein, we propose the utilization of moisture-induced electric field to boost carrier transfer at Schottky interface. This strategy is demonstrated viable in a flexible Schottky junctions comprising of an asymmetric graphene oxide (aGO) layer and an aluminum foil, which works by a new mechanism and outperforms existing flexible semiconductor-based DC nanogenerators by several orders of magnitude in both current density (81.06 A m⁻²) and power density (24.08 W m⁻²) and the mechanic-to-electricity conversion efficiency can achieve to 2.29%. In addition, because the nanogenerator can respond to both moisture and mechanical changes, it can also serve as a self-powered sensor to monitor human respiratory and body surface sweat levels simultaneously, so as to guide people in training more scientifically. This strategy would initiate a direction of next-generation wearable nanogenerators and sensors.