Direct growth of nitrogen-doped graphene films on glass by plasma-assisted hot filament CVD for enhanced electricity generation

Nitrogen (N) doping is an efficient way to modulate the properties of graphene. The reported chemical vapor deposition (CVD) processes for synthesizing N-doped graphene mostly involve a metal catalyst and ammonia (NH3) dopant. However, the inevitable metal residual and toxicity of NH3 would significantly hinder its practical applications. In this paper, for the first time, metal-free synthesis of N-doped graphene films on glass was achieved through a plasma-assisted hot filament CVD method using eco-friendly N-2 gas as the dopant. Both the hot filament and plasma source were proven to be essential for growing N-doped graphene of preferable quality. By adjusting the N-2 flow, the N content, transmittance and electrical properties of graphene films could be facilely modulated. Furthermore, it was demonstrated that the electrical voltage induced by dropping ion droplets on graphene glass was significantly improved from 50 mV to 320 mV through N doping, exceeding those of reported graphene based electricity generators. This improvement was attributed to the higher surface potential of N-doped graphene glass compared to the pristine ones, as revealed by Kelvin probe force microscopy. The present work provides a promising strategy for direct synthesis and expands applications of N-doped graphene glass for high-efficiency energy harvesting.