Electrochemical fabrication of copper(I) oxide electrodes for photoelectrochemical and photovoltaic applications

Colleen M McShane, Purdue University

Abstract

Cu2O is a low-cost and non-toxic semiconductor having a direct band gap (Eg = 1.9 to 2.2 eV) capable of utilizing visible light for solar energy conversion. It is of interest for photoelectrochemical applications because the valence and conduction bands of Cu2O are situated near the reduction and oxidation potentials of water, respectively. Consequently, it may be possible for Cu2O to produce hydrogen via direct water photolysis with little or no external bias necessary. There are only a few reported syntheses of n-Cu2O to date. Through the use of an acetate buffer, dendritic n-Cu2O electrodes were produced via electrodeposition. The dendritic morphology allowed for facile substrate coverage. In order to improve the photocurrent, the nucleation density and crystal domain size were systematically controlled through changes in the deposition potential, the Cu2+ concentration, and the acetate concentration. Due to copper vacancies in the lattice, Cu2O is typically prepared as a p-type material. Cu2O based photovoltaics have been based on p-Cu2O/metal Schottky junctions and p-Cu 2O heterojunctions. The use of n-type and p-type Cu2O to form a homojunction is considered a likely way to reach the theoretical efficiency of 12%. Few Cu2O p-n homojunctions have been prepared due to the previous lack of n-Cu2O. A Cu2O homojunction was fabricated by the electrodeposition of p-Cu2O from an alkaline copper lactate bath followed by the subsequent electrodeposition of n-Cu2O from slightly acidic copper acetate plating media. In order to investigate the effect of the junction morphology on the performance of polycrystalline Cu 2O homojunction solar cells, the morphology of the p-Cu2O layer was systematically modified to show only {100} or a combination of {100} and {111} planes at the p-n junction interface. Further studies explored the effect of contact material choice on the overall performance of Cu 2O homojunction solar cell. These studies allowed for locating the relative positions of the Fermi level energies of electrodeposited p- and n-Cu2O. Furthermore, as different morphologies and crystal habits can alter the surface reactivities and photoelectrochemical properties of polycrystalline electrodes, the systematic and rational tailoring of crystal morphologies is important. To this end, additives may be added to the deposition media. The effect of various additives (e.g., Cl-, CTAB, NH3, DMSO, ethylene glycol, glycerol) on the deposition of Cu2O electrodes was investigated. Also, the effect of using glycerol as a complexing agent was investigated.

Degree

Ph.D.

Advisors

Choi, Purdue University.

Subject Area

Chemistry|Physical chemistry

COinS