Electrochemical Etching of Zinc Oxide for Silicon Thin Film Solar Cell Applications

Abstract

A novel approach is presented for introducing a surface morphology with beneficial light scattering properties to sputter-deposited ZnO:Al films, which are used as front contact in Si thin film photovoltaic devices. Electrochemical anodization was used to trigger local dissolution, leading to interfacial structures complementary to those commonly prepared by an etching step in diluted HCl. By systematic variation of electrochemical etching conditions and electrolytes, the essential experimental parameters for designing the ZnO film surface were evaluated. The prepared films were characterized by scanning electron microscopy, four-point resistance and Hall measurements. Furthermore, electrochemical and chemical etching steps were combined to generate a diversity of different surface morphologies. The application of such films in microcrystalline Si single junction solar cells has shown promising initial results.

Nanostructuration and band gap emission enhancement of ZnO film via electrochemical anodization

“…3. Thus, there are two competing reactions involving ZnO film dissolution, as described below [11,[16][17][18]:…”

“…The mechanism of nanoporosity formation in ZnO films can be attributed to localized corrosion at grain boundaries, triggered by the reaction of ZnO film surface with etching agents in the electrolyte solution [11,19]. The ZnO etching behavior can be explained by the wurtzite structure and the dangling bond model, described in Ref [19].…”

“…For example, Pust et al [11] reported on the change of the surface morphology of RF-sputtered ZnO:Al thin films by means of an anodic electrochemical treatment in hydrochloric acid solution, for application as a front contact in Si thin film solar cells. In this work, the treatment of ZnO films in K 2 SO 4 solution allows the nanostructuration of the ZnO not only at the surface region, as reported by Pust et al [11], but also at the bulk region. In this paper, the correlation between morphology and surface chemistry of the ZnO films with band gap emission intensity enhancement, before and after electrochemical cycling, is also discussed.…”

Role of the dopant aluminum for the growth of sputtered ZnO:Al investigated by means of a seed layer concept

“…Besides self-textured TCOs such as SnO 2 :F or ZnO:B, 13 textured contact layers are produced by a post-deposition etching step of sputter-deposited ZnO:Al. 7,14,15 To ensure an etching morphology with appropriate light scattering properties, a careful adjustment of ZnO:Al deposition parameters such as pressure, temperature, 16 film thickness, 17 and target doping concentration (TDC) 8 is needed. However, conflicting requirements in terms of ZnO:Al deposition conditions prevail since conductivity, transparency, and surface texture need to be optimized simultaneously.…”

Fabrication of porous ZnO via electrochemical etching using 10wt% potassium hydroxide solution

“…Numerous studies have reported the uses of various fabrication methods, such as chemical vapor deposition [11], electrochemical deposition [12], wet chemical etching [13], and electrochemical etching [14], to produce nanostructured and porous-structured ZnO. However, to the best of our knowledge, only a limited number of studies have been carried out to produce porous ZnO via [14].…”