Molecule design and screening of novel unsymmetrical zinc phthalocyanine sensitizers for dye-sensitized solar cells.

The molecular orbital and optical properties of the dyes PCH001 and TT1 reported previously were studied using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The results show that the electronic spectra simulated for PCH001 and TT1 in ethanol were in good agreement with the experimental data. The molecular orbital spatial orientation was used to interpret the discrepancy of the photovoltaic performances of the PCH001 and TT1 sensitized solar cells. The conjugation between the carboxyl group and the phthalocyanine ring in TT1 was found to be better than that through the C-C single bond in PCH001, which may contribute to TT1's improved performance. Four new unsymmetrical phthalocyanine molecules with the peripheral substituents as donors and anchoring groups as acceptors, namely CZ1, CZ2, trans- and cis-CZ3, were designed and compared to PCH001 and TT1. The new molecules CZ2 and cis-CZ3 were promising and may challenge the current record of PCH001 and TT1 in phthalocyanine-sensitized solar cells.