Axial Thiophene-Boron(subphthalocyanine) Dyads and Their Application in Organic Photovoltaics

We report the synthesis and characterization of boron(subphthalocyanine) derivatives with bithiophene and quaterthiophene as axial ligands, i.e., thiophene-subphthalocyanine dyads (nT-SubPcs), and their application in organic photovoltaic cells (OPVs). Thin films of nT-SubPcs prepared via solution processing can act as the electron donor in bilayer OPVs with evaporated C-60 as the electron acceptor. The photophyscial and morphological properties of the nT-SubPcs are studied to rationalize OPV device parameters. The single-crystal X-ray structure is solved for two dyads to show the molecular structures in the solid state, and UV-vis spectroscopy and fluorescence spectroscopy are used to characterize the effect of conjugated thiophene ligands on the photophysical properties, i.e., absorption and photoluminescence quantum yield. Cyclic voltammetry, density functional theory (DFT) calculations, and low-temperature photoluminescence spectra show that photoluminescence yields depend on the overall flexibility of the SubPc derivatives and not on the oxidation potential or electronic relationship of the ligand and macrocycle molecular orbitals. We show with grazing-incidence X-ray scattering and atomic force microscopy (AFM) that careful choice of ligand structure can improve the crystallinity of thin films that leads to a relative increase in short-circuit current in OPV device. Our work clearly demonstrates that SubPcs can be used as light-harvesting chromophores in a matrix of a crystalline organic semiconductor for OPVs.