Pb-doped Cu3Se2 nanosheets: Electrochemical synthesis, structural features and optoelectronic properties

Abstract

Thin films of nanostructured un- and lead (Pb)-doped copper selenide (Cu3Se2) with various Pb concentrations were grown on fluorine-doped tin oxide (FTO) glass substrates through an electrochemical deposition method. The structural, optical, electrical and photovoltaic properties of the deposited films were studied using different techniques. The X-ray diffraction (XRD) patterns showed polycrystalline tetragonal structures for the Cu3Se2 nanostructures and the field emission scanning electron microscopy (FESEM) images exhibited that all deposited Cu3Se2 films contain nanosheets. The nanosheets of the Pb-doped samples were observed to be bent and fractured at edges. Furthermore, photoluminescence (PL) analysis of Cu3Se2 unraveled three emission bands in the ultraviolet, green and infrared regions and outlined a shift towards lower wavelengths (blue shift) for the near band edge (NBE) of the Pb-doped samples, compared with the un-doped sample. Also, the absorption spectra of the samples were analyzed to determine the optical energy band gap of the samples, which resulted in the value of 1.65 eV for the un-doped sample and demonstrated an increase in the optical energy band gap of Cu3Se2 upon adding Pb dopant and increasing its concentration. Finally, evaluation of the films as the absorber layer of solar cells indicated that there is a minimum amount of strain in the sample with the highest acceptor concentration, which affects its solar cell efficiency, positively.