Structure-activity Relationship Research Of Porphyrin Derivitives In Dye-sensitized Solar Cell

Dye-sensitized solar cells(DSSCs) is a new type of organic solar cells. Andporphyrin received wide attention in the application as sensitive dyes in DSSCs for itsunique photophysical and chemical properties. In this paper, we designed andsynthesized three categories, a total of12porphrin dyes. Structure-activityrelationship was investigated through comparing to the performance of these dyes andtheir structures.Meso-substituent symmetrical porphyrins were prepared through Alder methodas starting materials. Followed with formylation and metallization on β position toobtain intermediates Zn-1-0~Zn-4-0. The Knoevenagel condensation of Intermediatesand acrylic acid gave dyes1-1~4-1. Ester group was introduced through the Wittigreaction between intermediates and4-formylbenzoate triphenylphosphine, andcorresponding dyes1-2~4-2was obtained through the hydrolysis reaction. Themonobromination of symmetrical porphyrins gave intermediates Br-1~Br-4.Followed with metallization, Sonogashira coupling and hydrolysis reaction obtaineddyes1-3~4-3.Spectra analysis, electrochemical analysis and photoelectron conversionproperties were studied on these12porphyrin dyes. The UV-visiable spectra andemission spectra show that the maximum absorption wavelength of dyes areinfluenced by linker on β position geatly, but meso-substituents have little effect onthese aspect. Electrochemical analysis show all12dyes have the property that couldused in DSSCs. Photoelectron conversion properties show that same meso-substituent gives an opposite influence for different linkers with different mechanics.The matching degree of the length of linker and the size of meso-substituent could bea key point in porphyrin structure that affects the cell performance of the device basedon porphyrin sensitizers. When the meso-substituents are large to be a linker, thesteric hindrance of meso-substituent would caused the dye adopting relativelyparallel orientation to the TiO2surface and yielding to small surface coverage and lowcell performance. When the meso-substituents are small to a linker, there are morespace between the surface of TiO2and dyes, which could increase the possibility ofI3-penetrating the adsorbed dye layer, thus increasing the interfacial chargerecombination. Dye4-3gives the best performance in this paper, it gives a shortcircuit photocurrent density of11.50mA cm-2, an open-circuit voltage of0.70V, a fill factor of0.66, and a light to electricity conversion efficiency of5.32%under the AM1.5sunlight.