Dual-function graphene-based electronic devices

Abstract

Transparent electrodes are an essential element in numerous electronic devices, including displays, solar cells, LEDs, and touch panels for smartphones and tablets. Indium tin oxide (ITO) is currently the most dominant material for this purpose due to its good electrical and optical performance, and moisture resistance. However, indium is becoming a scarce and expensive resource and requires a costly vacuum deposition process. In addition, its mechanical properties are weak, which severely restricts its application in flexible electronics. These issues have stimulated numerous developments with the aim of discovering new transparent electrode materials. Graphene has recently attracted considerable attention as an alternative to ITO due to its good electrical conductivity, optical transparency, and high mechanical strength.1, 2 However, for adoption in practical electronic devices, the electrical conductivity of graphene must be made comparable to that of ITO.3, 4 Although a chemical doping method has been developed, the initially high conductivity tends to degrade due to the adsorption of moisture and other chemical molecules under environmental conditions. As an alternative approach to overcoming these limitations, we have developed a nonvolatile doping method using a piezoelectric material as substrate5 that could pave the way toward the application of graphene in high-performance flexible and transparent devices. Our electrostatic doping method employs the ferroelectric polarization of a piezoelectric material, which can effectively enhance the conductivity of graphene while maintaining good mechanical and optical properties, without degradation. After a poling process in which the material is subjected to large voltages (50–150V), the carbonfluorine dipoles of the ferroelectric poly(vinylidene fluorideco-trifluoroethylene)—P(VDF-TrFE)—polymer align along the poling direction. In other words, the net negative charge of the Figure 1. (a) Image of a graphene/poly(vinylidene fluoride-cotrifluoroethylene)/graphene (GPG) device. The device is interconnected with a sound source to measure acoustic actuation, a red LED to measure its performance as a nanogenerator, and an amplifier. Inset shows the structure of GPG multilayer film. Two graphene layers work as top and bottom electrodes for the central poly(vinylidene fluoride-cotrifluoroethylene)—P(VDF-TrFE)—layer. (b) Schematic depiction of the dual functionality of the device as an acoustic actuator and a nanogenerator.