Huihua Deng

Improvement in photoelectric conversion of a phthalocyanine-sensitized TiO2 electrode by doping with porphyrin

Abstract The effect of doping with tetrasulfonated zinc porphyrin (ZnTsPP) on photoelectric conversion of a nano-structured titanium dioxide (TiO2) electrode sensitized with tetrasulfonated gallium phthalocyanine (GaTsPc) is reported. Doping with ZnTsPP greatly enhances the photocurrent response at long wavelength (the GaTsPc Q band of 640∼760 nm), with 20- and 60-fold improvement of the quantum efficiency at 680 and 700 nm, and results in an improvement of photoelectric conversion for the liquid junction solar cell based on the co-sensitized TiO2 electrode, although the photocurrent response in the Soret band of ZnTsPP is markedly decreased with 8-fold drop of the quantum efficiency at 430 nm. This may be attributed to the formation of the Pc/PP heteroaggregates on the nano-structured TiO2 electrode, resulting in the decreases of the concentration of GaTsPc dimers and the possible presence of a low-lying charge-transfer state.

Co-sensitization of microporous TiO2 electrodes with dye molecules and quantum-sized semiconductor particles

Abstract The microporous titanium dioxide (TiO2) film has been prepared on a conducting glass substrate. A seven-fold enhancement in energy conversion efficiency of the dye-sensitized solar cell was achieved by pre-depositing a closely packed TiO2 thin film on the surface of the conducting glass. Moreover, FeS2 particles were coated on TiO2 electrode by chemical reaction of iron pentacarbonyl with sulfur in xylene. Both atomic force microscope (AFM) and photoelectric studies suggest that the FeS2 quantum-sized particles play a dominate role in the photoelectric conversion of FeS2/TiO2 electrode, while the FeS2 large particles have less or even no contribution to the photo-current. Furthermore, the TiO2 electrode has been co-modified with phthalocyanine dye molecules and quantum-sized semiconductor particles. Co-sensitization of the TiO2 electrode with CdSe particles and ZnTCPc dye molecules not only extends the photoresponse of CdSe/TiO2 electrode further into red region, but also improve the quantum efficiency of photoelectric conversion. We believe that such a co-sensitization technique should be of general importance in designing novel solar energy conversion devices.

Photosensitization of TiO2 semiconductor with porphyrin

Zn-tetrasulfophenylporphyin (ZnTSPP), stable colloidal TiO2 and a transparent microporous TiO2 electrode have been prepared. The interaction of ZnTSPP with colloidal TiO2 was studied by absorption and fluorescence spectroscopy, the apparent association constant for the association between ZnTSPP and TiO2 nanoparticles is about 1.6 × 104 M−1. ZnTSPP adsorbed on colloidal TiO2 can participate in the sensitization process by injecting electrons from its excited states into the conduction band of TiO2. Upon excitation of its absorption band, 90% of the fluorescence emission of ZnTSPP could be quenched by colloidal TiO2 and the maximum of incident photon to current efficiency is 51.3% at 427 nm with a 10 μm thick TiO2 film sensitised by ZnTSPP.

Influence of molecular aggregation and orientation on the photoelectric properties of tetrasulfonated gallium phthalocyanine self-assembled on a microporous TiO2 electrode

Abstract The photoelectric conversion and surface photovoltage spectrum (SPS) of tetrasulfonated gallium phthalocyanine (GaTsPc) molecules self-assembled on a microporous titanium dioxide (TiO 2 ) electrode are reported. For comparison, the SPS of the GaTsPc sublimed film deposited at 10°C is also presented. The GaTsPc molecule exists mainly in the aggregated form on the microporous TiO 2 electrode and in the sublimed film. The photocurrent action spectrum and SPS have shown that only the absorption of the GaTsPc monomers leads to a photocurrent or photovoltage while GaTsPc cofacial aggregates do not generate a photocurrent and photovoltage. This is attributed to a perpendicular or titled orientation of the molecular planes in the GaTsPc molecular aggregates on the microporous TiO 2 electrode.

Aggregation and the photoelectric behavior of tetrasulfonated phthalocyanine adsorbed on a TiO2 microporous electrode

Abstract Absorption spectroscopy of tetrasulfonated Zn, Co, Ga, In, TiO and metal-free phthalocyanine on a transparent titanium dioxide film electrode, which is made up of interconnected particles and pores characterized by scanning electron microscopy, has been reported. The chemical modification of the TiO 2 microporous electrode with tetrasulfonated phthalocyanine (MTsPc) extends its absorbance into the visible region. The tetrasulfonated phthalocyanine mainly exists as the dimer on the TiO 2 microporous electrode. The photocurrent action spectroscopy shows that only the absorbance of the MTsPc monomer contributes to the photocurrent while that of the MTsPc dimer does not generate a photocurrent.

The mixed effect of phthalocyanine and porphyrin on the photoelectric conversion of a nanostructured TiO2 electrode

Abstract The mixed effect of tetrasulfonated gallium phthalocyanine (GaTsPc) and tetrasulfonated zinc porphyrin (ZnTsPP) on the photoelectric conversion is reported. For the liquid junction solar cell based on the cosensitized TiO 2 electrode, cosensitization greatly enhances the photocurrent response at the longer wavelength (the GaTsPc Q band) and markedly decreases the photocurrent response in the Soret band of ZnTsPP. The decrease of the Soret band of ZnTsPP is offset by the improvement of the Q band of GaTsPc, resulting in the mixed effect in the short-circuit photocurrent. This is attributed to the formation of Pc/PP heteroaggregates on the cosensitized TiO 2 electrode, resulting in the decreases of the concentration of GaTsPc dimer and the presence of the low-lying charge-transfer state.

Cosensitization of a nanostructured TiO2 electrode with tetrasulfonated gallium phthalocyanine and tetrasulfonated zinc porphyrin

Abstract The cosensitization of a nanostructured TiO2 electrode with the spectral complementary dyes, tetrasulfonated gallium phthalocyanine (GaTsPc) and tetrasulfonated zinc porphyrin (ZnTsPP), is reported. For the liquid junction cell based on a nanostructured TiO2 electrode cosensitized with GaTsPc and ZnTsPP molecules, cosensitization extends the absorbance into the region 400–750 nm, resulting in an improvement of the light-harvesting efficiency and short-circuit photocurrent on illumination at 35.7 mW cm−2. The photocurrent response at 685 nm, corresponding to the absorbance of the GaTsPc monomer, is strongly enhanced, probably due to the decrease in the surface concentration of GaTsPc molecular dimers and the possible formation of an extended π system in GaTsPc/ZnTsPP heteroaggregates resulting from cosensitization of the electrode.

The liquid junction cell based on the nanostructured TiO2 electrode sensitized with zinc tetrasulfonated phthalocyanine

Abstract High-surface-area TiO 2 film has been deposited on an indium tin oxide (ITO) conducting glass substrate from colloidal suspension. Atomic force microscope and scanning electron microscope analyses show that the TiO 2 electrode is made up of nanometer-sized and interconnected TiO 2 particles and pores. The specific surface area of the TiO 2 electrode is determined by the size of particles and the thickness of the film and can be measured to be 270 by the absorption spectrum study of the TiO 2 electrode sensitized with zinc tetrasulfonated phthalocyanine (ZnTsPc). A liquid junction cell based on the ZnTsPc/nanostructured TiO 2 electrode has been fabricated and harvests 20% of the incident solar energy flux. Under monochromatic illumination at λ = 700 nm, the incident-photon-to-current conversion efficiency (IPCE) is about 2.1% and the quantum efficiency, considering the actual absorption of the incident light, is 7%. The conversion efficiency reaches 1.7% under an illumination of 35 mW cm −2 , which presents one of the highest values reported for phthalocyanine photovoltaic devices. The pre-deposition of the conducting TiO 2 thin layer with the closely packed structure gives rise to the improvement in photoelectric performance of the solar cell, which is due to the formation of the liquid junction in the interface between the TiO 2 electrode and electrolyte.

Cosensitization and photoelectric conversion of a nanostructured TiO2 electrode with tetrasulfonated porphyrins

The cosensitization of a nanostructured titanium dioxide (TiO n 2) electrode with tetrasulfonated porphyrins (MTsPP; M=Zn, H n 2) is reported. Cosensitization greatly enhances the photocurrent response at the Q band of H n 2TsPP, with tenfold improvement of the quantum efficiency at 690 nm, and markedly decreases the photocurrent response in the Soret band of ZnTsPP with six-fold drop of the quantum efficiency at 430 nm. The maximum of the quantum efficiency at 690 nm reaches 14.5% on monochromatic illumination at 16.0 µW cm n -2 when the TiO n 2 electrode is cosensitized with H n 2TsPP (0.40) and ZnTsPP (0.60). The photoelectric behavior of the cosensitized TiO n 2 electrode is attributed to the formation of heteroaggregates between H n 2TsPP and ZnTsPP molecules during the cosensitization of the TiO n 2 electrode, resulting in a decrease of the surface concentration of H n 2TsPP dimers and the presence of a low-lying charge-transfer state.

Improvement in Photoelectric Conversion of a Nanostructured TiO2 Electrode Cosensitized with Phthalocyanine and Porphyrin

The cosensitization of a nanostructured titanium dioxide (TiO2) electrode with tetrasulfonated gallium phthalocyanine (0.39) and tetrasulfonated zinc porphyrin (0.61) greatly enhances the photocurrent response in the GaTsPc Q band (640–760 nm), with sixtyfold improvement in the quantum efficiency at 700 nm, and markedly decreases the photocurrent response in the Soret band of ZnTsPP, with an eightfold drop of the quantum efficiency at 430 nm. The quantum efficiency of 32.2% at 700 nm is obtained for monochromatic illumination at 13.8 µW·cm-2, which presents one of the highest efficiencies reported for long wavelengths. This is attributed to the formation of the Pc/PP heteroaggregates on the cosensitized TiO2 electrode resulting from charge-transfer interaction.