Substituent effects on zinc phthalocyanine derivatives: A theoretical calculation and screening of sensitizer candidates for dye-sensitized solar cells

A series of unsymmetrical phthalocyanine sensitizer candidates with different donor and acceptor substituents, namely ZnPcBPh, ZnPcBOPh, ZnPcBtBu, ZnPcBN(Ph)2, ZnPcBNHPh, ZnPcBNH2, ZnPcBNHCH3 and ZnPcBN(CH3)2, were designed and calculated using density functional theory (DFT) and time-dependent DFT calculations. The molecular orbital energy levels, the molecular orbital spatial distributions and the electronic absorption spectra of the ZnPcB series molecules were compared with those of TT7 and TT8 to reveal the substituent effects of different donor and acceptor groups on the phthalocyanine compounds and select good sesitizer candidates. The results show that some of these compounds have considerably smaller orbital energy gaps, red-shifted absorption bands and better charge-separated states, causing them to absorb photons in the lower energy region. Several new absorption bands emerge in the 400–600 nm region, which makes it possible for them to become panchromatic sensitizers. This characteristic is superior to the phthalocyanine sensitizers reported previously, including the current record holder, PcS6. The sensitizer candidates screened in the current work are very promising for providing good performance and might even challenge the photon-to-electricity conversion efficiency record of 4.6% for phthalocyanine sensitizers.

A series of unsymmetrical phthalocyanine sensitizer candidates with different donor and acceptor substituents were designed and calculated through density functional theory calculations. The molecular orbital energy levels, the molecular orbital spatial distributions and the electronic absorption spectra of them were compared with those of TT7 and TT8. The sensitizer candidates screened are found very promising to provide good performances, even possible to challenge the photon-to-electricity conversion efficiency record of 4.6% of phthalocyanine sensitizers because of their lower orbital energy gaps, better charge separation states and the new absorption bands emerged in the 400–600 nm regions.Figure optionsDownload high-quality image (194 K)Download as PowerPoint slideHighlights
► The candidates bearing N bridging donors possess red-shifted absorption bands than TT7 and TT8.
► Some new absorption bands emerged in the 400–600 nm region.
► The candidates are promising to provide higher efficiencies than that of TT7 and TT8 or even PcS6.