Fabrication of high-performance composite electrodes composed of multiwalled carbon nanotubes and glycerol-doped poly(3,4-ethylenedioxythiophene):polystyrene sulfonate for use in organic devices
In this study, composite films composed of highly conductive multiwalled carbon nanotubes (MWCNTs) and poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) were fabricated via additional organic-compound doping. The effects of glycerol (GL) or dimethyl sulfoxide (DMSO) doping on the film properties, such as surface roughness, work function (Φ), and conductivity, were studied for both PEDOT:PSS and MWCNT/PEDOT:PSS composite systems. The interactive couplings between the PEDOT and PSS molecules became disordered upon doping with GL or DMSO, which altered the conjugated structure between the PEDOT and PSS chains. Therefore, the electrical conductivity of the PEDOT:PSS and MWCNT/PEDOT:PSS films was enhanced by the addition of GL or DMSO molecules. The GL-doped PEDOT:PSS (PEGL) and ultraviolet (UV)-oxidized MWCNT/PEDOT:PSS (0.2-UVGL) films exhibited comparable work functions (PEGL = 4.87 eV, 0.2-UVGL = 5.0 eV). They also had lower sheet resistances (Rs; PEGL = 806.7 ± 50 Ω □−1, 0.2-UVGL = 613 ± 120 Ω □−1) as compared to those of the undoped PEDOT:PSS (Φ = 4.92 eV, Rs = 1.03 ± 0.10 MΩ □−1) and MWCNT/PEDOT:PSS composites (Φ = 4.7 eV, Rs = 2184 ± 244 Ω □−1). Furthermore, because of these excellent electrical properties, the doped MWCNT/PEDOT:PSS films showed great potential as the source/drain electrode in an organic thin-film transistor and as the catalytic counter electrode in a dye-sensitized solar cell. In conclusion, devices with 0.2-UVGL electrodes performed better than the corresponding devices with other MWCNT/PEDOT:PSS composite electrodes and the device characteristics were comparable to that of standard devices with platinum/fluorine-doped tin oxide electrodes.