On the electrochemical synthesis and characterization of p-Cu2O/n-ZnO heterojunction

Abstract

A p-Cu2O/n-ZnO heterojunction was grown directly on fluorine-doped tin oxide (FTO) substrate by two-step electrodeposition in aqueous solution. The electrical characteristics of the p-Cu2O/FTO and n-ZnO/FTO were studied using the Mott-Schottky (M-S) analysis in the electrolyte solution. High donor and acceptor concentrations were obtained for ZnO and Cu2O layers, respectively. The p-Cu2O/n-ZnO heterojunction show long electron lifetime and high electron–hole separation efficiency according to the electrochemical impedance spectroscopy (EIS) measurements and photocurrent response. The morphological, structural, optical, and electrical characteristics of p-Cu2O/n-ZnO heterojunction were investigated by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), UV–Vis and photoluminescence (PL) analysis. The FE-SEM cross-section images confirm the formation of well-defined cubic Cu2O grains on continuous and flat surface of ZnO layer. XRD result points to high crystallinity of (111)-oriented p-Cu2O layer on (101)-oriented n-ZnO layer. The optical band gap energies of n-ZnO and p-Cu2O thin film are 3.3 and 2.3 eV, respectively. The current–voltage (I–V) characteristics of Au/p-Cu2O/n-ZnO/FTO heterojunction shows well-defined rectifying behavior with turn on voltage of 0.5 V in dark and high photoresponse under illumination.