Solid-state electropolymerization and doping of triphenylamine as a route for electroactive thin films

Abstract

Solid-state electropolymerization could be a way to produce organic semiconductors with potential application as Hole Transporting Materials (HTMs) in hybrid organic-inorganic devices. Thereby, thin solid films of triphenylamine (TPA) deposited by spin coating on conducting glass substrates have been electrochemically treated by performing multiple voltammetric cycles between -0.4 V and 1.0 V vs. Ag/AgCl in a 0.5 M sodium perchlorate aqueous electrolyte. Subsequent characterization by means of in situ UV-Vis spectroscopy, in situ Electrochemical Quartz Crystal Microbalance, Atomic Force Microscopy, Contact Angle analysis, and Open Circuit Potential measurements reveals cross-linking of the monomeric units in the thin film. Such polymerized films are characterized by a high electroactivity linked to doping/undoping, a reversible electrochromic behavior under potentiodynamic conditions and fast changes of the open circuit potential upon illumination, indicating efficient charge transport throughout the film. While extensive polymerization has been demonstrated for TPA, this process is negligible in the case of tri-p-tolylamine, which is linked to the para substitution of the phenyl rings. In more general vein, the feasibility of solid-state electropolymerization is illustrated as well as the potential advantages of this methodology for the preparation of hybrid inorganic/organic materials based on nanoporous oxide matrices.

Characterization and Polymerization of Thienylphenyl and Selenylphenyl Amines and Their Interaction with CdSe Quantum Dots

“…This type of behavior has been previously ascribed to an oxidative solid-state electrochemical cross-linking. [15][16][17]34] In agreement, it has been previously reported that TTPA can be electrochemically polymerized from solution, generating an amorphous conducting polymer. [29][30][31] After about 40 cycles, an apparent stable response is observed: the oxidation process starts at 0.45 V in both films, while the corresponding reduction peak is observed at about 0.55 (TTPA) and 0.61 V (TSePA).…”

“…The original spectra of TTPA and TSePA are characterized by the presence of a broad band at l < 450 nm, which can be ascribed to the onset of the p-p* transition. This band is displaced toward longer wavelengths compared with that of the triphenylamine molecule [34] due to the presence of thiophene and selenophene units. [35] After voltammetric cycling, a new band develops in both films, the onset of which is located at around 500 nm for TTPA and 550 nm for TSePA.…”

Electropolymerized Highly Photoconductive Thin Films of Cyclopalladated and Cycloplatinated Complexes

“…5 nm, as seen for instance in Figure 11(a) for complex 2 electrodeposited at 250 mV/s scan rate. For lower scan rates, AFM images reveal a higher roughness of the film surface (R RMS = 22 nm) and show a cauliflower-like texture similar in features to films of TPA obtained through solid-state electropolymerization 39 (Figure 11b). …”

A solid-state CdSe quantum dot sensitized solar cell based on a quaterthiophene as a hole transporting material

“…Importantly, the oxidation onset is located around 0.1 V less positive than in the case of QT12 and, therefore, the valence band for pTPA would be located at À5.43 eV, that is, 0.1 eV less negative than the QT12 HOMO level. The UV-vis spectra given for pTPA in our previous report 31 QT12 (in the ESIw) allow us to estimate the HOMO-LUMO difference as 3.26 and 2.76 eV, respectively. On the other hand, the conduction band of TiO 2 (at the isoelectric point) has been located at À4.2 eV.…”