No abstract

A series of meso-tetraphenylzincporphyrins have been prepared to examine the effects of the porphyrin substituents and adsorption conditions on photovoltaic properties of the porphyrin-sensitized TiO 2 cells. The cell performance strongly depended on the linking bridge between the porphyrin core and the TiO 2 surface, the bulkiness around the porphyrin core, and the immersing solvents and times for the porphyrin adsorption. In particular, the high cell performance of the porphyrin-sensitized TiO 2 cells was achieved when protic solvent (i.e., methanol) and short immersing time (0.5-1 h) were used for the conditions of the dye adsorption on TiO 2 , which is in sharp contrast with Ru dye-sensitized TiO 2 cells. The highest cell performance was obtained with 5-(4-carboxyphenyl)-10,15,20-tris(2,4,6-trimethylphenyl)porphyrinatozinc(II) as a sensitizer and methanol as an immersing solvent with an immersing time of 1 h: a maximal incident photon-to-current efficiency of 76%, a short circuit photocurrent density of 9.4 mA cm -2 , an open-circuit voltage of 0.76 V, a fill factor of 0.64, and a power conversion efficiency of 4.6% under standard AM 1.5 sunlight. These results will provide basic and valuable information on the development of dye-sensitized solar cells exhibiting a high performance.

Novel perylene imide derivatives with both electron-donating and bulky substituents have been synthesized for dye-sensitized solar cells. The power conversion efficiency reached 2.6%, which is the highest value among perylene-sensitized TiO2 solar cells.

A novel strategy for constructing a vertical arrangement of bicontinuous donor-acceptor arrays on a semiconducting electrode has been developed. The relationship between the film structure and the photoelectrochemical properties has been elucidated as a function of the number of donor layers for the first time. The maximum incident photon-to-current efficiency value (21%) is comparable to the highest value (20%) reported for vertical arrangements of bicontinuous donor-acceptor arrays on electrodes.

King of the spins is provided by the mixed‐valent Mn19 aggregate as reported by A. K. Powell et al. in their Communication on page 4926 ff. The use of bridging azido ligands leads to a completely ferromagnetically coupled system with a record ground spin state of 83/2. This remarkable molecule has been investigated and characterized by scientists from three laboratories working together in the European Network of Excellence “MAGMANet”, the logo of which provides the background to the cover picture.

Novel unsymmetrically π-elongated porphyrins, in which the naphthyl moiety is fused to the porphyrin core at the naphthyl bridge with a carboxyl group (fused-Zn-1) or at the opposite side of the phenyl bridge with a carboxyl group (fused-Zn-2), have been synthesized to improve the light-harvesting abilities in porphyrinsensitized solar cells. As the results of π-elongation with low symmetry, Soret and Q bands of fused-Zn-1 and fused-Zn-2 were red-shifted and broadened, and the intensity of Q-band relative to that of Soret band was enhanced. The fused-Zn-1 and fused-Zn-2-sensitized TiO 2 solar cells showed the power conversion efficiencies (η) of 4.1% and 1.1%, respectively, under standard AM 1.5 conditions. The η value of the fused-Zn-1 cell was improved by 50% compared to the reference cell using unfused porphyrin (Zn-1). The fused-Zn-1-sensitized cell revealed high IPCE (incident photon-to-current efficiency) values of up to 55%, extending the response of photocurrent generation close to 800 nm. Thus, the improved photocurrent generation of the fused-Zn-1-sensitized cell relative to the Zn-1-sensitized reference cell is responsible for the remarkable difference in the η values. The η value of the fused-Zn-2 cell was much lower than that of the fused-Zn-1 cell. DFT calculations disclosed that there are significant electron densities on the carboxyl group in the LUMO of fused-Zn-1, whereas there are little electron densities on the carboxyl group in the LUMO of fused-Zn-2. Accordingly, the larger electronic coupling between the porphyrin and the TiO 2 surface in the fused-Zn-1-sensitized cell may be responsible for the high cell performance, due to the efficient electron injection from the porphyrin excited singlet state to the conduction band of the TiO 2 electrodes. To further improve the cell performance, 5-(4-carboxylphenyl)-10,15,20-tetrakis-(2,4,6-trimethylphenyl)porphyrinatozinc(II) (Zn-3), possessing different light-harvesting properties, was coadsorbed with fused-Zn-1 onto an TiO 2 electrode. Under the optimized conditions, the cosensitized cell yielded maximal IPCE value of 86%, short circuit photocurrent density of 11.7 mA cm -2 , open-circuit voltage of 0.67 V, fill factor of 0.64, and η of 5.0% under standard AM 1.5 conditions.

Liquid crystalline donor (i.e., phthalocyanine) was covalently linked to acceptor (i.e, fullerene) to achieve efficient charge-transport properties in a liquid crystalline phase. The columnar structure exhibited highly efficient ambipolar charge-transport character, demonstrating the potential utility of the strategy in organic electronics.

A novel naphthyl-fused zinc porphyrin carboxylic acid has been synthesized and employed successfully in a dye-sensitized TiO2 solar cell, with a power conversion efficiency of 4.1%, which is improved by 50% relative to the unfused porphyrin reference cell.