Investigation of detailed physical properties and solar cell performances of various type rare earth elements doped ZnO thin films

Abstract

In this study the structural, optical, electrical properties and solar cell performance of undoped ZnO and rare earth (RE) doped ZnO (Zn0.95Yb0.05O, Zn0.95Eu0.05O and Zn-0.90 Eu0.05Yb0.05O) thin films prepared by sol-gel spin coating method were investigated. The structural characterizations of the obtained samples were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses. The optical properties of these thin films were carried out with UV-vis transmittance spectroscopy technique in 350-800 nm range. The electrical properties of films were examined by resistance measurements at room temperature. XRD results show that all samples have single phase wurtzite (hexagonal) structure with (002) c-plane orientation. Detailed structural characterizations were examined from XRD data. SEM analysis represents that nanoparticles are formed on the thin films and the type of dopant affected the morphologies, thickness and sizes of ZnO nanostructures. Our optical results indicate the average optical transmittances of RE doped ZnO samples are 98% at different regions in the visible region. Also the band gap energy of all of thin films was calculated from optical transmittance spectroscopy data using Tauc equation. The band gap energies of undoped, Yb, Eu, and Eu/Yb co-doped ZnO were found as 3.307, 3.295, 3.29 and 3.28 eV, respectively. Urbach energy was calculated from spectral absorption coefficient and this value shows an increase with doping Eu and Yb elements. It was observed that the electrical resistivity of doped samples is low compared to ZnO thin film. Also, in this study the rare earth elements effects on the solar cell performance of ZnO nanostructures were investigated and it was seen that Yb and Eu elements improve the cell performance.