Graphene for Transparent Electrodes and Organic Electronic Devices - Organic Solar Cells: Materials and Device Physics - page 94

4.4 Graphene for All-Carbon Electronics
With its remarkable electronic and mechanical properties, graphene exhibits great
potential in the preparation of all-carbon electronics. For the research of low-cost and
flexible all-carbon devices or integrated circuits (ICs) based on graphene, one key is
to develop an easy method to fabricate the device with simple process such as spin
coating, inkjet printing, etc. Graphene films prepared by reduction of graphene oxide
demonstrate some great advantages, especially when they are used as electrode
materials with transparency requirement. In this section, we will give a brief intro-
duction of graphene-based all-carbon electronics mainly based on our recent works.
4.4.1 All-Carbon Flexible FET
OFETs are the essential building blocks for state-of-the-art and next-generation
electronics, which exhibit the advantages of low cost, large-area flexibility, etc. To
fully exploit these advantages in practical applications, solution fabrication pro-
cesses are strongly desired. Currently, metals like gold (Au) are widely used for
the source/drain (S/D) electrodes in the fabrication of OFETs on SiO 2 /Si substrates
with doping Si as the gate (G) electrode, which make it difficult to achieve fully
flexible, solution-processed, and low-cost devices. Thus, electrode materials with
high carrier injection efficiency, excellent interface compatibility with organic
semiconductors, and, especially, easy solution processability and suitability for use
in flexible electronics are in high demand. As an alternative electrode material,
graphene has demonstrated great potential to fulfill above requirements. Bao et al.
have reported that OFET devices fabricated with rGO as bottom-contact electrodes
have been demonstrated with lower contact resistances compared with those
fabricated with gold contacts and desirable morphological features [ 53 ]. Recently,
our group has fabricated OFETs using rGO for all the electrodes (source, drain,
and gate) for the first time [ 54 ]. Patterned graphene electrodes and OFETs were
fabricated as outlined in Fig. 4.8 , Graphene was used for all S/D/G electrodes, and
polyimide (PI) was used as the dielectric layer. In the device fabrication, the G
electrode (graphene), dielectric layer PI, and S/D electrodes (graphene) were all
fabricated by solution processes on a flexible PI substrate. These OFETs show
performance comparable to corresponding devices using Au electrodes as the S/D
electrodes on SiO 2 /Si substrates with n-doped Si as the gate electrode. Also, these
devices demonstrate excellent flexibility without performance degradation over
severe bending cycles.
4.4.2 All-Carbon Flexible OPV
For all-carbon flexible OPV, metal electrodes should not be incorporated in the
device. As discussed above, graphene acts as window electrode, the back electrode