Graphene, the last representative sp 2 carbon material to be isolated, acts as an ideal material platform for constructing flexible electronic devices. Exploring a new method to fabricate high-quality graphene films with high throughput is essential for achieving greater performance with flexible electronic devices. Here, we report a facile coating and subsequent illumination method for mass-fabricating highly crystalline photoreduced graphene oxide (PRGO) films directly onto conductive substrates. The direct fabrication of PRGO films onto Cu foils with partial oxygenated groups, an intensive stacked highly crystalline structure, and reduced graphene oxide regions enable significant performance enhancements when used as supercapacitor electrodes compared with other graphene-only devices, exhibiting high specific capacitances of 275 F g À1 at a scan rate of 10 mV s À1 and 167 F g À1 at 1 V g À1 with excellent rate capability. The as-established all-solid-state flexible supercapacitors exhibit superior flexibility and robust mechanical stability, resulting in a capacitance delay of only 2% after performing 100 bending cycles. The demonstrated PRGO films provide a promising material platform to realize a broad range of applications related to flexible electronics devices.
INTRODUCTIONFlexible electronic devices have garnered considerable attention because of the benefits enabled by large-area, lightweight, flexible electrode films, which have the potential to enable unique advances in future mobile applications, such as wearable displays, roll-up solar cells, electronic skin and flexible energy storage. 1,2 Graphene films containing a few layers or multiple layers of two-dimensional graphene sheets are prominent contenders as attractive components for use in flexible electronic devices due to their high conductivity, chemical stability and mechanical flexibility. 3,4 For the practical applications of graphene in these fields, scalable production of macroscopic-scale graphene films is required rather than the current micrometer-sized graphene sheets. To date, the synthesis of large-scale flexible graphene films has mainly been demonstrated by two approaches. One approach is the 'bottom-up' synthesis strategy, by which high-quality graphene can be prepared using chemical vapor deposition to grow graphene at high temperature, followed by a transfer procedure to place graphene films onto flexible substrates; 5 however, this method is not sufficiently cost-and time-effective to be commercially viable for mass production and requires a difficult post-functionalization step to produce the appropriate graphene films. Another approach is the 'top-down' method, that is, solution