CVD graphene has been n-and p-doped using redox-active, solutionprocessed metal-organic complexes. Electrical measurements, photoemission spectroscopies, and Raman spectroscopy were used to characterise the doped films and give insights into the changes.The work function decreased by as much as 1.3 eV with the n-dopant, with contributions from electron transfer and surface dipole, and the conductivity significantly increased.

The design of polymer semiconductors possessing effective π–π intermolecular interactions coupled with good solution processability remains a challenge. Structure‐property relationships associated with side chain structure, π–π intermolecular interactions, polymer solubility, and charge carrier transport are reported for a donor–acceptor(1)‐donor–acceptor(2) polymer: 5‐Decylheptadecyl (5‐DH), 2‐tetradecyl (2‐DT), and linear n‐octadecyl (OD) chains are substituted onto a polymer backbone consisting of terthiophene units (T) between two different electron acceptors, benzothiadiazole (B), and diketopyrrolopyrrole (D), pTBTD, to afford pTBTD‐5DH, pTBTD‐2DT, and pTBTD‐OD, respectively. In the 5‐DH side chain, the branching position is remote from the polymer backbone, whereas it is proximal in 2‐DT. This study demonstrates that incorporation of branched side chains where the branching position is remote from the polymer backbone merges the advantages of improved solubility from branched units with effective π–π intermolecular interactions normally associated with linear chains on conjugated polymers. pTBTD‐5DH exhibits superior qualities with respect to the degree of polymerization, solution processability, π–π interchain stacking, and charge carrier transport relative to the other analogs. pTBTD‐5DH exhibits a field‐effect hole mobility of up to 2.95 cm2 V–1 s–1, a factor of 3–7 times that achieved with pBDT6‐DT and pBDT6‐OD.

3-Aminopropyltriethoxysilane (APTES) and perfluorooctyltriethoxysilane (PFES) were used to modify the interface between transferred CVD graphene films and its supporting dielectric to create n-type and p-type graphene, respectively. A graphene p-n junction was obtained by patterning both modifiers on the same dielectric and verified through the creation of a field effect transistor (FET). Characteristic I-V curves indicate the presence of two separate Dirac points which confirms an energy separation of neutrality points within the complementary regions. This method minimizes doping-induced defects and results in thermally stable graphene p-n junctions for temperatures up to 200 °C.

The effect of vacuum annealing followed by exposure to oxygen and water vapor on the unintentional doping of CVD-grown graphene was investigated. CVD graphene samples were cycled between room temperature and 500 °C in vacuum while in situ Raman measurements were recorded. During the heating and cooling cycle, a hysteresis in the Raman response due to the desorption of p-dopants was observed. Upon exposure to O2 gas or air, a blue shift in the Raman response with respect to the as grown film was observed which was due to increased adsorption of p-dopants on the sample. Experiments showed that a combination of water vapor and oxygen is more effective in p-doping the samples than just oxygen and that the doping effects are reversible in both cases. Electrical measurements performed on back-gated field effect graphene devices indicate that shifts in the Dirac point correlate well to the shifts in the Raman peak positions as well as changes found in XPS and Kelvin Probe measurements, verifying the changes in doping of the graphene.

A series of benzothiadiazole oligothiophene and oligo(thienylene vinylene) donor−acceptor (D−A) copolymers were synthesized and characterized. These low optical band gap materials (∼1.5 eV) are capable of absorbing photons in the range of 400−800 nm and exhibit good thermal stability. Their hole mobilities, determined using an organic field-effect transistor (OFET) architecture, vary over a range of 3 orders of magnitude and strongly correlate with the molecular ordering and morphology of the respective thin films. Spin-coated films of the poly(benzothiadiazole-sexithiophene) PBT6, which exhibits a highly crystalline lamellar π−π stacked edge-on orientation on the OFET substrate, possesses a hole mobility of ca. 0.2 cm 2 /V•s. Vinylene-containing analogs PBT6V2 and PBT6V2′ are amorphous and exhibit very low mobilities. The molecular weight of PBT6 has a strong influence on the electronic properties: a sample with a lower molecular weight exhibits a mobility approximately 1 order of magnitude lower than the high molecular weight homologue, and the absorption maximum is appreciably blue-shifted. The hole mobility of PBT6 is further enhanced by a factor of ca. 3 through fabrication of the OFET by drop casting. OFETs fabricated by this process exhibit mobilities of up to 0.75 cm 2 /V•s and I ON/OFF ratios in the range of 10 6 − 10 7 . These results demonstrate the potential of incorporating benzothiadiazole units into polythiophene derivatives to develop high-mobility semiconducting polymers.