Sascha E. Pust

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

A novel approach is presented for introducing a surface morphology with beneficial light scattering properties to sputterdeposited ZnO:Al films, being used as front contact in Si thin film photovoltaic devices. Electrochemical anodization was used to trigger local corrosion, 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, sensible experimental parameters were evaluated for the preparation of ZnO films that can be applied in Si thin film solar cells. The prepared films were characterized by scanning electron microscopy, four-point resistance and Hall measurements. Furthermore, the kinetics of the heterogeneous interfacial reaction during the corrosion process were studied utilizing electroanalytical techniques. This allowed the identification of the processes occurring at the solid/liquid interface. Application of such films in microcrystalline Si single junction solar cells has shown promising initial results.

Electrochemical texturing of Al-doped ZnO thin films for photovoltaic applications

The processes during chemical and electrochemical etching of Al-doped ZnO are investigated utilizing a scanning flow cell setup with online detection of dissolved Zn ions. The rate of chemical dissolution was found to be a linear function of buffer and proton concentration in near neutral pH solutions according to a transport limited reaction. In contrast, electrochemical etching is limited by the kinetics of the reaction and increases linearly with the imposed current density. Due to this fundamental difference, the dissolution of Zn can be either uniform over the whole surface or highly localized at active sites like grain boundaries. A combined approach of chemical etching and the well-controllable galvanostatic dissolution thus allows a fine adjustment of the ZnO:Al surface texture for applications in silicon thin film photovoltaic cells in order to improve their overall energy conversion efficiency.