We designed highly efficient porphyrin sensitizers with two phenyl groups at meso-positions of the macrocycle bearing two ortho-substituted long alkoxyl chains for dye-sensitized solar cells; the ortho-substituted devices exhibit significantly enhanced photovoltaic performances with the best porphyrin, LD14, showing J(SC) = 19.167 mA cm(-2), V(OC) = 0.736 V, FF = 0.711, and overall power conversion efficiency η = 10.17%.

Novel zinc porphyrins with 1-4 π-conjugated phenylethylnyl (PE) units (labeled PE1-PE4) as a link of controlled length were synthesized for fundamental tests and applications as a dye-sensitized solar cell (DSSC). The UV-visible spectra of the solution samples show clear absorption patterns of the PE groups in a region 300-400 nm, consistent with results calculated with density-functional theory. Cyclic voltammograms of PE1-PE4 in tetrahydrofuran show similar electrochemical potentials for each compound. Femtosecond fluorescence up-conversion of solution samples and of porphyrin-sensitized TiO 2 films was measured with excitation at 420 or 430 nm and emission at 460, 470, 620, and 680 nm. When these porphyrins were fabricated into DSSC devices, the efficiency of power conversion of these devices decreased systematically with increasing length of the link: 2.5 ( 0.2% (PE1), 2.0 ( 0.1% (PE2), 0.78 ( 0.09% (PE3), 0.25 ( 0.02% (PE4). This great photovoltaic degradation from PE1 to PE4 is not interpretable according to the rate of electron injection independent of length; other factors, including electron transfer from the semiconductor back to the porphyrin cation or the electrolyte, must be considered to account for the observed dependence of photovoltaic performance on length.

Zinc porphyrins in a series bearing a phenylethynyl, naphthalenylethynyl, anthracenylethynyl, phenanthrenylethynyl or pyrenylethynyl substituent, denoted LD1, LD2, LD3a, LD3p or LD4, respectively, were prepared as photosensitizers for dye-sensitized solar cells. The overall efficiencies of the corresponding devices show a trend LD4 > LD3p > LD2 > LD3a > LD1. Significantly, LD4 features J SC /mA cm À2 ¼ 19.627, V OC /V ¼ 0.711, and FF ¼ 0.721, giving an efficiency h ¼ 10.06% of power conversion. This value is superior to that of a N719-based solar cell fabricated under similar experimental conditions. The remarkable performance of the LD4 cell is rationalized to be due to the broader and more red-shifted spectral feature that makes the IPCE spectrum to cover broadly across the entire visible region, 400-800 nm.

A series of acene-modified zinc porphyrins (benzene to pentacene, denoted as LAC-1 to LAC-5) were prepared to study their absorption spectra, electrochemical properties, and photovoltaic properties. For the absorption spectral changes in THF, porphyrin B bands are red-shifted and broadened from 449 to 501 nm for LAC-1 to LAC-3, showing the effect of additional π-conjugation. In contrast, the B bands of LAC-4 and LAC-5 are blue-shifted. In addition, the tetracenyl group of LAC-4 gives rise to absorption bands in between B and Q bands. On the other hand, the Q bands of LAC-1 to LAC-5 are systematically broadened and red-shifted from 629 to 751 nm. By comparison, the absorption bands of LAC porphyrins on TiO2 films are broadened and slightly shifted. Fluorescence emission maxima of LAC porphyrins in THF are also systematically red-shifted from LAC-1 to LAC-5. Cyclic voltammetry experiments in THF/TBAP show that the first reductions are systematically positive-shifted from −1.16 to −0.85 V vs SCE for LAC-1 to LAC-5, indicating the effect of increasing π-conjugation. As for the performance of DSSCs using LAC porphyrins, the overall efficiencies are LAC-1 (2.95%), LAC-2 (3.31%), LAC-3 (5.44%), LAC-4 (2.82%), and LAC-5 (0.10%). Overall efficiency of a LAC-3-sensitized solar cell is nearly twice of that of a LAC-1-sensitized solar cell and is about 81% overall efficiency of N719-sensitized solar cells under the same experimental conditions. The conversion efficiency of incident photons to current (IPCE) experiments shows that the broadened absorption bands of LAC-3 effectively minimizes the gap between B and Q bands, contributing to the improved DSSC performance. The very poor performance of LAC-5 is suggested to be caused by rapid nonradiative relaxation of the molecule in the singlet excited state.