Study On Photoelectric Conversion Characteristics Of Cuprum Phthalocyanine/Perylene Diimide Molecular Systems

Characteristic of electron transporting is a determinative factor to valuethe performances of photoelectric conversion systems. In the organic photo-electric conversion functional systems, this kind of characteristic lies on theinteraction between different molecules of working materials, which isdecided by the molecular structures.Cuprum phthalocyanine/perylene diimide, a system commonly used inthe research of organic solar cell, was selecteded as a model to check therelationship between the changes of molecular structures (mainly the changesof their substituents) and photoelectric conversion parameters. Six kinds ofperylene diimide derivatives were designed and consequently synthesized,and two types of cuprum phthalocyanine derivatives with differentsubstituents were selected. We also designed spray titanium dioxide filmelectrode experimental device. Accordingly, di-dye and mono-dyephotoelectric conversion systems made of cuprum phthalocyanine derivativesand perylene diimide derivatives were prepared and their photoelectricconversion parameters were measured. Finally, molecular orbit energy wascalculated by Gaussian98 program, and relationships between the case ofmolecular orbital energy matching and the characteristics of photoelectricconversion in the di-dye and mono-dye systems were discussed.The results showed that because of the difference of substituents inphthalocyanine/perylene diimide systems, their open-circuit voltage, photo-current density and incident monochromatic photon-to-current conversionefficiency (IPCE) changed markedly. When electron-donor molecule keptunchanged in the di-dye systems, photoelectric conversion characteristicswere improved with the substituents of electron-acceptor molecule changingfrom electron withdrawing groups to electron donating groups, and whenelectron-acceptor molecule kept unchanged, characteristics of photoelectricconversion were improved with changing the substituents of electron-donormolecule from electron donating groups to electron withdrawing groups. Inthe mono-dye systems, electron-donor molecules with substituents of electrondonating groups had predominance of transporting electrons, which could alsoimprove the photoelectric conversion characteristics. These results showedthat the changes of substituents between electron-donor and electron-acceptormolecules had important effects on photoelectric conversion characteristics.Therefore, the criteria to select working materials in the organic photo-electric conversion functional systems are as following: first, the effects onelectron transporting caused by molecular structures of working materialsshould be considered as well as absorption wavelengths of working materialsand the case of molecular orbital matching between those working materials;second, electron-donor molecules with electron withdrawing substituentscombined with electron-acceptor molecules having electron donatingsubstituents could form a structure of donor-accptor-donor/accptor-donor-accptor(a-D-a/d-A-a), which would favor the process of electron transport-ing and then improve the characteristics of photoelectric conversion in di-dyesystems;last, in mono-dye systems, electron-donor molecules withsubstituents of electron donating groups have predominance of transportingelectrons, which could improve the photoelectric conversion characteristics.