**2.1. Processability**

A major obstacle in the synthesis and processing of bulk-quantity graphene sheets is the preparation of monolayer graphene and its insolubility, with the latter being responsible for poor handling and manipulation during graphene processing.[34, 35] Graphene has a strong tendency to cluster together into aggregation, caused by the electrostatic forces and the strong π–π interaction between individual graphene flakes, which make further manipulation and device fabrication using graphene difficult.[36] For this reason, covalent and noncovalent manners for modification of graphene have been developed for exfoliation and dispersion of graphene.[37] Besides, by derivatizing graphene with different moieties, the solubility of graphene can be tuned to suit varied solvents needed for different applications. For example, chemically grafted CH2OH-terminated regioregular poly(3-hexylthiophene) (P3HT) onto carboxylic groups of graphene oxide (GO) *via* amidation reaction; the resultant P3HT-grafted GO sheets are soluble in common organic solvents, which facilitates the structure/property characterization and the device fabrication by solution processing.[38]
