Role of Interfacial Interactions in the Graphene-Directed Assembly of Monolayer Conjugated Polymers

Development of graphene-organic hybrid electronics isone of the most promising directions for next-generation electronicmaterials. However, it remains challenging to understand the graphene-organic semiconductor interactions right at the interface, which is key todesigning hybrid electronics. Herein, we study the influence of grapheneon the multiscale morphology of solution-processed monolayers ofconjugated polymers (PII-2T, DPP-BTz, DPP2T-TT, and DPP-T-TMS). The strong interaction between graphene and PII-2T wasmanifested in the highfiber density and highfilm coverage of monolayerfilms deposited on graphene compared to plasma SiO2substrates. Themonolayerfilms on graphene also exhibited a higher relative degree ofcrystallinity and dichroic ratio or polymer alignment, i.e., higher degree of order. Raman spectroscopy revealed the increasedbackbone planarity of the conjugated polymers upon deposition on graphene as well as the existence of electronic interaction acrossthe interface. This speculation was further substantiated by the results of photoelectron spectroscopy (XPS and UPS) of PII-2T,which showed a decrease in binding energy of several atomic energy levels, movement of the Fermi level toward HOMO, and anincrease in work function, all of which indicate p-doping of the polymer. Our results provide a new level of understanding ongraphene-polymer interactions at nanoscopic interfaces and the consequent impact on multiscale morphology, which will aid in thedesign of efficient graphene-organic hybrid electronics.