Photoconductivity enhancement and charge transport properties in a conjugated polyelectrolyte/carbon nanotube hybrid studied by scanning probe microscopy

We report the use of electrostatic force microscopy (EFM) and photoconductive atomic force microscopy (PCAFM) for the characterization of a cationic conjugated polyelectrolyte/multi-walled carbon nanotube (MWCNT) hybrid. The polymer, poly[N,N,N-triethyl-12-(thiophen-3-yl)dodecan-1-ammonium bromide] (PTETDA) may functionalize MWCNTs by noncovalent interactions, and can also enhance the photosensitivity of the resulting polymer/MWCNT hybrid. Molecular dynamics simulation shows that the PTETDA interacts with the MWCNT mainly through the conjugated backbone and the counterions can diffuse away from PTETDA. The unscreened charges were detected by EFM, providing evidence for the presence of the PTETDA wrapped on the MWCNTs. This is the first report that EFM is applied in the characterization of a polymer/MWCNT hybrid. PCAFM shows that the equilibrium conductance exhibited a one-fold increase upon white light illumination at 1.45 mW cm−2. The current–voltage curves were analyzed by the Simmons model to investigate the mechanism of the photoresponse. We also report for the first time that a rigorous advanced bootstrap method was applied to analyze the photocurrent response of nanoparticles. The enhancement in photoconductivity demonstrates the potential of using a conjugated polymer/carbon nanotube hybrid in optoelectronic devices.