Three-dimensional high-rate electropolymerized thin film with exceptionally high photocurrent based on a triphenylamine-containing ruthenium complex

Unusual Photoelectrochemical Properties of Electropolymerized Films of a Triphenylamine-Containing Organic Small Molecule

“…Stable and rapidly responding photocurrents were observed and monotonically increased as the biases became more negative from +0.6 to −0.4 V versus SCE, indicating that interfacial electron transfer occurred from thin-film-modified ITO to electrolyte solution and the photocurrents generated by the films were the cathode photocurrent, which is similar to the behaviors of some Ru­(II)-complex-based electrostatic self-assembled films previously reported. , It was found that the maximum photocurrent (photocurrent densitiy) of 2.66 μA (9.6 μA/cm 2 ) was achieved at −0.4 V for the poly­( L ) 1 film. In comparison to Table , it is worth mentioning that a significant cathode photocurrent density of 2.2 μA/cm 2 at a bias potential of 0 V was observed for the poly­( L ) 1 film, which outperforms or is comparable to those previously reported for some representative molecule-based thin films under similar experimental conditions. ,,,,,,,− …”

“…On the basis of the data shown in Figure c and eqs and of Laviron’s theory, the k s value could be calculated where α is the electron transfer coefficient and ν a and ν c are the critical scan rates, which were obtained to be ν a = ν c = 0.1429 V/s by linearly fitting the anodic and cathodic data of Figure c, respectively. An apparent k s value of the poly­( L ) 1 film was determined to be 5.66 s –1 , which is greater or comparable to k s values previously reported for Ru III/II -associated redox reactions in a [(H 2 L 1 )­Ru­(H 2 L 2 )­Ru­(H 2 L 1 ) 2 ]­(ClO 4 ) 4 {H 2 L 1 = 2,6-bis­(2-benzimidazolyl)­pyridine; H 2 L 2 = 2,6-bis­(4-([2,2’:6′,2″-terpyridin]-4′-yl)­phenyl)-1,5-dihydrobenzo­[1,2- d :4,5- d ′]­diimidazole}-based drop-casting film (3.1 s –1 ) and a [Ru­(bpy) 2 (Hdppip)]­(ClO 4 ) 2 {Hdppip = 2-(2,6-di­(pyridin-2-yl)­pyridine-4-yl)-1 H -imidazo­[4,5- f ]­[1,10]­phenanthroline}-based electrostatic film with graphene oxide (5.5 s –1 ) and 17-fold as fast as a value of 0.33 s –1 that we recently reported for a TPA •+1/0 -associated redox reaction in an electropolymerized film poly­[Ru­(ppip) 3 ] 1 {ppip = N -phenyl- N -(4-(1-phenyl-1 H -imidazo­[4,5- f ]­[1,10]­phenanthrolin-2–2-ylphenyl)­benzenamine} . As shown in Figure d, the corrected k s value was calculated to be 5.89 s –1 by replacing E p – E ° with solution ohmic drop E p – E ° – iR s , which was very close to the apparent k s value, where R s is the solution resistance measured by electrochemical impedance spectroscopy (EIS) to be 29.1 Ω.…”

“…As shown in Figure 8, poly(L) n (n = 1−6) exhibited a significant cathodic photocurrent (photocurrent density), which decayed from 0.62 μA (2.20 μA/cm 2 ) for n = 1 to 0.24 μA (0.86 μA/cm 2 ) for n = 6 when irradiated with 100 mW/cm −2 white light (730 > λ > 325 nm) at bias potential of 0 V versus SCE in 0.1 M Na 2 SO 4 aqueous solution. The filmthickness-induced decay in photocurrents is a phenomenon that the photocurrents do not respond to the increases in lightharvesting capacity of the film, is common for thin-filmmodified electrodes, 11 and could be due to the fact that the increase in the light-harvesting capacity is offset by the increased interfacial charge-transfer resistance plus photogenerated carrier recombination. 51 We further studied the influence of bias voltages on the photocurrent polarity of the poly(L) 1 film in degassing 0.1 M Na 2 SO 4 aqueous solution.…”

“…Thin-film materials of functional molecules, such as organic small molecules/polymers and metal complexes, have attracted intensive attention in photoelectronic applications, such as solar cells, light-emitting diodes, thin-film transistors, flexible displays, and electrochromic cells. − The film deposition techniques, such as electropolymerization, − covalent self-assembly, spin coating and drop casting, , electrostatic self-assembly, and electrospray, can usually be used for fabricating thin films of functional molecules. Among these techniques, electropolymerization presents the following competitive advantages: easy operation, cost-effective instrumentation, very rapid simultaneous realization of electrosynthesis of polymers and separation of the polymers and monomers, controllable film coverage and thickness, and varying structures and doping degrees by simply changing electropolymerization parameters, such as electropolymerization time or the number of potential sweep cycles and precursor molecules, , although spin coating and electrospray have been used in industry for film fabrication.…”

“…Pure organic dyes as dyes for DSSCs and photoelectrochemical cells have advantages of easy synthesis and no noble metals compared to polypyridyl Ru­(II) complexes that have been recognized to be “star” dyes. Applications of electropolymerized films in DSSCs ,, and photoelectrochemical cells , have been poorly explored in comparison to those of the other types of films. Herein, we report electropolymerization films of an easily accessible and low-cost TPA-based organic molecule, exhibiting rapid quasi-reversible redox and significant photocurrent generation properties.…”