Surface ligand effects in MEH-PPV/TiO2 hybrid solar cells

TiO2 nanorods (NRs) were synthesized by hydrolysis of titanium tetraisopropoxide (TTIP) using oleic acid (99%) as surfactant at low temperatures (80–100 °C) and are modified with different ligands: oleic acid (OLA), n-octyl-phosphonic acid (OPA) and thiophenol (TP) in order to investigate the effect of surface ligand on the excition dissociation and the charge transport in hybrid MEH-PPV/TiO2 photovoltaic (PV) cells. The morphology and crystalline form of as-prepared TiO2 NRs are examined by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD) and Raman spectrometer (RS). The FTIR analysis confirms all the ligands coordinated with the Ti center of TiO2 NRs. The optical properties of the modified TiO2 NRs are characterized by UV–vis absorption spectra and photoluminescence (PL) spectra. Thiophenol modified TiO2 NRs quench the PL of MEH-PPV more effectively than OLA-TiO2 NRs and OPA-TiO2 NRs. The power conversion efficiency of hybrid PV cells from thiophenol modified TiO2 NRs and MEH-PPV is the highest among the investigated TiO2 NRs.