Photocurrent Enhancement Of N-type Cu_2o Electrodes Achieved By Controlling Dendritic Branching Growth

摘要

Cu_2O electrodes composed of dendritic crystals were produced electrochemically using a slightly acidic medium (pH 4.9) containing acetate buffer. The buffer played a key role for stabilizing dendritic branching growth as a pH drop during the synthesis prevents formation of morphologically unstable branches and promotes faceted growth. Dendritic branching growth enabled facile coverage of the substrate with Cu_2O while avoiding growth of a thicker Cu_2O layer and increasing surface areas. The resulting electrodes showed n-type behavior by generating anodic photocurrent without applying an external bias (zero-bias photocurrent under short-circuit condition) in an Ar-purged 0.02 M K_2SO_4 solution. The zero-bias photocurrent of crystalline dendritic electrodes was significantly higher than that of the electrodes containing micrometer-size faceted crystals deposited without buffer. In order to enhance photocurrent further a strategy of improving charge-transport properties by increasing dendritic crystal domain size was investigated. Systematic changes in nucleation density and size of the dendritic Cu_2O crystals were achieved by altering the deposition potential, Cu~(2+) concentration, and acetate concentration. Increasing dendritic crystal size consistently resulted in the improvement of photocurrent regardless of the method used to regulate crystal size. The electrode composed of dendritic crystals with the lateral dimension of ca. 12000 μm~2 showed more than 20 times higher zero-bias photocurrent than that composed of dendritic crystals with the lateral dimension of ca. 100 μm~2. The n-type nature of the Cu_2O electrodes prepared by this study were confirmed by linear sweep voltammetry with chopped light and capacitance measurements (i.e., Mott-Schottky plots). The flatband potential in a 0.2 M K_2SO_4 solution (pH 6) was estimated to be -0.78 vs Ag/AgCI reference electrode. The IPCE measured without applying an external bias was approximately 1% for the visible region. With appropriate doping studies and surface treatment to improve charge transport and interfacial kinetics more efficient n-type Cu_2O electrodes will be prepared for use in various photoelectrochemical and photovoltaic devices.