Design, computational screening and synthesis of novel non-peripherally tetra hexylthio-substituted phthalocyanines as bulk heterojunction solar cell materials

Abstract

New bulk heterojunction organic solar cell materials of phthalocyanines (Pcs) were designed, screened computationally and synthesized for the first time in a study with the aim of finding more efficient products. The electronic absorption spectrum and the molecular orbital properties of the novel non-peripherally tetrasubstituted Pcs were investigated by DFT/TDDFT calculations. The screened compounds were found to be promising for providing good performance on BHJ solar cells with their small band gaps, red-shifted absorption bands in near infrared region, deep HOMO energy levels and high electron mobilities. Furthermore, the model of Scharber et al. (2006) was used for open-circuit voltage (Voc) prediction for the first time for Pcs as the donor moiety and calculated eVoc values up to 0.56 was found with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor moiety. All studied Pcs except one were found to provide energetic driving force for Pc-PCBM cells computationally. Hence, the new precursor 3-hexylthio phthalonitrile (3) was obtained by the nucleophilic aromatic substitution of 3-nitrophthalonitrile (1) and 1-hexanethiol (2) and then cyclotetramerized in the presence of metal salts and/or DBU to achieve a series of non-peripherally tetrahexylthio substituted phthalocyanines (4–12). The phthalocyanines with lead, indium and manganese metal centres have red-shifted Q bands as well as non Q-band absorptions in the 450–600nm region. The precursor and the targeted phthalocyanines were characterized comprehensively by 1H NMR, 13C NMR, FT-IR, UV–Vis, mass spectroscopies.