Photovoltage method for the research of CdS and ZnO nanoparticles and hybrid MEH-PPV/nanoparticle structures

Abstract

The paper demonstrates an application of photovoltaic effect in the research of nanomaterials and hybrid structures of polymers with nanoparticles. Photovoltage (PV) measurement was utilized for estimating the size of CdS and ZnO nanoparticles and diagnostics of hybrid structures with poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), namely nano-CdS/MEH-PPV and nano-ZnO/MEH-PPV. CdS average nanocrystal diameters 4.0 and 4.8 nm were calculated from the onset values of energies corresponding to the steep increase in the PV signals using the effective mass model. The range of size of ZnO particles was from about 5 up to 50 nm. Nanoparticle distribution obtained by transmission electron microscopy (TEM) measurements shows that the calculated diameters agree fairly well with the size of nanoparticles with the highest occurrence. The PV spectrum represents a sum of the spectra corresponding to the various nanoparticle sizes. The distribution of the nanoparticles was also obtained by a simple mathematical treatment of the PV spectra, and agreement with the results of TEM was found. PV and TEM measurements were performed on commercial CdS and ZnO nanoparticles and on CdS nanoparticles prepared in our laboratory. We employ triethanolamine as a protective agent to cover the surface of CdS nanoparticles. Nano-CdS/MEH-PPV and nano-ZnO/MeH-PPV hybrid structures were prepared, and influence of the particles on charge transport was shown by the PV spectra measurements.