The covalent grafting through a rigid ester bond of a dimeric porphyrin [(H 2 P) 2 ] and carbon nanohorns (CNHs) was accomplished. The newly formed CNH−(H 2 P) 2 hybrid was found to be soluble or dispersible in several organic solvents. Application of diverse spectroscopic techniques verified the successful formation of the CNH−(H 2 P) 2 hybrid material. In addition, thermogravimetric analysis revealed the amount of (H 2 P) 2 loading onto CNHs, and TEM studies showed the characteristic secondary spherical superstructure morphology of the hybrid material. Efficient fluorescence quenching of (H 2 P) 2 in the CNH−(H 2 P) 2 hybrid suggests that photoinduced events occur from the photoexcited (H 2 P) 2 to CNHs. Nanosecond transient absorption spectroscopy revealed the formation of transient species such as (H 2 P) 2•+ and CNH •− by photoinduced charge separation in CNH−(H 2 P) 2 . Additional proof for the photoinduced charge-separated state CNH •− −(H 2 P) 2•+ was obtained, from which the electron mediates to added hexyl viologen dication (HV 2+ ). Finally, the CNH−(H 2 P) 2 was adsorbed on nanostructured SnO 2 electrode, to construct a photoactive electrode, which reveals photocurrent and photovoltage responses with an incident photon-to-current conversion efficiency value as large as 9.6%, without the application of any bias voltage.

Two novel porphyrin-porphyrin dyads, the symmetrical Zn[Porph]-Zn[Porph] (2) and unsymmetrical Zn[Porph]-H2[Porph] (4), where Zn[Porph] and H2[Porph] are the metalated and free-base forms of 5-(4-aminophenyl)-10,15,20-triphenylporphyrin, respectively, in which two porphyrin units are covalently bridged by 1,3,5-triazine, have been synthesized via the stepwise amination of cyanuric chloride. The dyads are also functionalized by a terminal carboxylic acid group of a glycine moiety attached to the triazine group. Photophysical measurements of 2 and 4 showed broaden and strengthened absorptions in their visible spectra, while electrochemistry experiments and density functional theory calculations revealed negligible interaction between the two porphyrin units in their ground states but appropriate frontier orbital energy levels for use in dye-sensitized solar cells (DSSCs). The 2- and 4-based solar cells have been fabricated and found to exhibit power conversion efficiencies (PCEs) of 3.61% and 4.46%, respectively (under an illumination intensity of 100 mW/cm(2) with TiO2 films of 10 μm thickness). The higher PCE value of the 4-based DSSC, as revealed by photovoltaic measurements (J-V curves) and incident photon-to-current conversion efficiency (IPCE) spectra of the two cells, is attributed to its enhanced short-circuit current (J(sc)) under illumination, high open-circuit voltage (V(oc)), and fill factor (FF) values. Electrochemical impedance spectra demonstrated shorter electron-transport time (τd), longer electron lifetime (τe), and high charge recombination resistance for the 4-based cell, as well as larger dye loading onto TiO2.

No abstract

In this report we describe the use of a novel porphyrin triad (PPT) consisting of two zinc-metalated porphyrin units and one free-base porphyrin unit covalently linked through their peripheral amino-phenyl groups to a central s-triazine unit, in combination with PC 70 BM ([6,6]-phenyl C 70 butyric acid methyl ester), as electron donor and electron acceptors, respectively, for the fabrication of small-molecule based, solution-processed, bulk heterojunction (BHJ) organic solar cells. Photoluminescence studies of PPT:PC 70 BM blend films indicated that charge transfer is possible from PPT to PC 70 BM molecules. The solutionprocessed BHJ organic solar cell with the PPT:PC 70 BM blend in 1:1 weight ratio, processed from THF, was found to exhibit an overall power conversion efficiency (PCE) of 2.85%. When the BHJ active layer of PPT:PC 70 BM was processed from a 5% v/v mixture of 1-chloronaphathalene (CN) in THF, the PCE of the solar cell was increased up to 3.93%. This was attributed to the enhancement of the short circuit current J sc of the solar cell, which was ascribed to a stronger and broader incident photon to current efficiency (IPCE) response and to the higher degree of crystallinity of the active layer of the latter solar cell. The different surface morphologies of the two differently processed active layers result in different electron transport kinetics, and, as shown by electrochemical impedance spectra (EIS) and relaxation time measurements, the device with the active layer with the higher degree of crystallinity results in faster charge transfer process and more efficient exciton dissociation at the PPT/PC 70 BM interface.

A propeller-shaped, triazine-linked, unsymmetrical porphyrin triad -consisting of two zinc-metallated porphyrin units and one free-base porphyrin unit that is functionalized by a carboxylic acid -has been synthesized by stepwise amination reactions of cyanuric chloride. Photophysical, electrochemical, and DFT studies of the triad revealed no significant electronic interactions between the porphyrin units in the triad ground state but frontier orbital energy levels suitable for use as sensitizer in dye-sensitized solar cells (DSSCs). Furthermore, the triad can be described as a 2D-π-A system (D: donor, A: acceptor) that has the potential to promote electron transfer and injection into the TiO 2 electrode. Solar cells sensitized by the triad were fabricated with two different TiO 2 photoanodes, one processed by the paste-coating (PC) method and the other by the electrophoretic deposition (EPD)[a]