Nickel tetraphenylporphyrin doping into ZnO nanoparticles for flexible dye-sensitized solar cell application

In this study, we report on ZnO-based flexible dye-sensitized solar cells (DSCs) doped with different concentrations of 5,10,15,20-tetraphenyl-21H,23H-porphyrin nickel(II) (NiTPP). The photoelectrodes were prepared by blade coating, followed by a hot-compression technique. The effects of NiTPP doping on the surface morphology, structural, optical, and photovoltaic properties were studied. The surface morphology was observed by scanning electron microscopy (SEM), which confirmed the presence of NiTPP particles and also some aggregated particles visible at higher doping concentrations. The structural properties were examined by X-ray diffraction analysis and Raman spectroscopy, which confirmed the hexagonal wurtzite ZnO structure. The crystallite size of the ZnO nanoparticles (NPs) increased while the lattice strain decreased with increasing NiTPP doping concentration. The increment in the crystallite size might have induced light scattering inside the film to some extent. Optical absorption spectra showed the broadening of the spectrum in the lower-wavelength region, and a new absorption peak appeared (at 422 nm) as an effect of NiTPP doping. The red and blue shifts were observed for that peak as an effect of various doping concentrations. The Raman study of the films showed that there is no significant changes in the ZnO or NiTPP crystallite structure because of the NiTPP doping at different concentrations. Photocurrent-voltage (I-V) analysis showed that the 0.7%-NiTPP-doped cell attained the highest light-to-electric conversion efficiency of 2.7% in this investigation, which was about 42% higher than that of a non-NiTPP-doped cell. (C) 2017 The Japan Society of Applied Physics