Abstract In order to determine the sequence of elements in a cascade organic photovoltaic cell the geometry and electronic structure of mix-substituted phthalocyanines of А3В-type (where A is a donor and B is an acceptor group) were studied. The optimization of geometric parameters, the calculation of the frontier orbitals energies and band gaps (ΔЕ) of the studied homologous series of the "push-pull" type phthalocyanine derivatives and fullerene C60 were performed by the DFT/B3LYP/6-311++G** method. It is shown that the introduction of different nature substituents into benzene fragments of phthalocyanine leads to a significant change in the length of the C–C and N–C bonds as well as influences the energies of the frontier orbitals (HOMO/LUMO). The introduction only of donor substituents (–ОСН3) substantially increases energies of frontier orbitals. The substituents of different nature: donor (–ОСН3) and acceptor (–Cl) introduced simultaneously decrease ΔЕ and change values of the dipole moment of molecules. It is established that the elongation of alkoxy-substituents (n > 3) does not affect the HOMO/LUMO energies and ΔЕ values as the frontier orbitals are delocalized within macrocyclic fragment of phthalocyanine molecules. On the basis of the performed calculations the optimal sequence of the studied mix-substituted phthalocyanine derivatives and fullerene in photovoltaic cell is proposed.
Keywords: "push-pull" phthalocyanines, fullerene, energy of frontier orbitals, band gap, photovoltaic cell