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

Abstract

Development of graphene−organic hybrid electronics is one of the most promising directions for next-generation electronic materials. However, it remains challenging to understand the graphene− organic semiconductor interactions right at the interface, which is key to designing hybrid electronics. Herein, we study the influence of graphene on the multiscale morphology of solution-processed monolayers of conjugated polymers (PII-2T, DPP-BTz, DPP2T-TT, and DPP-T-TMS). The strong interaction between graphene and PII-2T was manifested in the high fiber density and high film coverage of monolayer films deposited on graphene compared to plasma SiO 2 substrates. The monolayer films on graphene also exhibited a higher relative degree of crystallinity and dichroic ratio or polymer alignment, i.e., higher degree of order. Raman spectroscopy revealed the increased backbone planarity of the conjugated polymers upon deposition on graphene as well as the existence of electronic interaction across the 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 an increase in work function, all of which indicate p-doping of the polymer. Our results provide a new level of understanding on graphene−polymer interactions at nanoscopic interfaces and the consequent impact on multiscale morphology, which will aid in the design of efficient graphene−organic hybrid electronics.

Diagnosis of doped conjugated polymer films using hyperspectral imaging

“…23 Another prototypical conjugated polymer poly(bisdodecylquaterthiophene) (PQT) shows highest electrical conductivity of 350 S/cm after introducing sulphur atoms into the side chains and doped with NOBF 4 . 24 The alteration of energy levels due to chemical structure modification facilitates integer charge transfer between the polymer and the dopants 21,25 , where the microstructure of the doped polymer film plays a dominant role in controlling electrical conductivity. The modification of sidechains with certain atoms promotes the interaction between the side chains and dopant molecules, thus increasing the lamellar distance while closely packing the polymer backbone, which promotes the charge transport along the - stacking direction.…”

“…12–15 Among various conjugated polymer families, polythiophene derivatives show the most promising optical and electrical characteristics where the electrical conductivity is significantly improved through structural modifications, doping strategies, and by controlling the microstructure through process optimization. 16–21…”

“…[12][13][14][15] Among various conjugated polymer families, polythiophene derivatives show the most promising optical and electrical characteristics where the electrical conductivity is signicantly improved through structural modications, doping strategies, and by controlling the microstructure through process optimization. [16][17][18][19][20][21] The electrical conductivity of the most commonly used poly(3-hexylthiophene-2,5-diyl) (P3HT) doped with 2,3,5,6-tetrauoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) is around 10 S cm −1 , 22 which increases to 100 S cm −1 when the P3HT structure is modied with ethylene glycol side chains. 23 Another prototypical conjugated polymer poly(bisdodecylquaterthiophene) (PQT) shows the highest electrical conductivity of 350 S cm −1 aer introducing sulphur atoms into side chains and upon doping with NOBF 4 .…”

Study of Molecular-Level Dispersion of Pristine Graphene in Aqueous Media via Polyvinyl Alcohol Coil Physisorption

“…Prior studies showed that the oxide or chemically modified graphene with different functional groups could be dispersed in polar or nonpolar solvents. − However, a significant disadvantage of this method is the destruction of π-orbitals in graphene and the deterioration of its electrical conductivity and mechanical properties. ,− Instead of using environmentally hazardous organic solvents and surfactants, − it seems reasonable to use biodegradable polymers as stabilizers in aqueous media to achieve better stability and higher nanosheet concentrations. , Using this method, the obtained colloidal solution provides an ideal starting material for graphene-based nanocomposite preparation. − In particular, the colloidal solution obtained has a high graphene/polymer ratio that can be used in 3d printing, membranes, and other electrical devices. ,, …”

“…23−25 In particular, the colloidal solution obtained has a high graphene/polymer ratio that can be used in 3d printing, membranes, 26 and other electrical devices. 24,27,28 The polymer assisting exfoliation mechanism is often correlated to the steric forces formed between polymer chains adsorbed physically or chemically on atomic surfaces. 29 Polymer-covered nanosheets induce a repulsive force between each other, which prevents further agglomeration.…”