Influence of the thickness on optical properties of sprayed ZnO hole-blocking layers dedicated to inverted organic solar cells

The sprayed pyrolysis technique was carried out to prepare ZnO thin films with different thickness dedicated to the optimization of the growth process of the multi-layers constituting inverted polymer solar cells in the aim to achieved better efficiency in photovoltaic energy conversion. The optical constants and dispersion energy parameters of the zinc oxide thin films were determined using optical characterization method. The transmittance measurements showed that all samples have high transparencies in the visible range, as generally used by solar cells. The band gap is slightly increased from 3.28 to 3.30 eV with the film thickness varying from 446 to 645nm. The oscillator energy E-0 and the dispersion energy E-d were deducted. The real and imaginary parts of dielectric constant for ZnO thin films were also determined. (C) 2014 Elsevier Ltd.