Thin Film Group
Novel Glass Texturing Method for Thin-Film PV
For cost-effective poly-Si thin-film solar cells, a good light trapping scheme is very important. Texturing methods such as reactive ion etching (RIE) of glass substrates or textured thin conductive oxides (TCOs) such as ZnO have been widely investigated. Besides improving optical performance, a texture must be compatible with the process steps used to fabricate the PV device. Since the purpose of thin-film PV technology is to reduce the cost of solar cells, we use glass as a low-cost substrate and texture the glass to enhance light trapping.
In 2003 we developed and patented a promising new method of texturing glass substrates, called Aluminium-Induced Texture (AIT) [1]. The AIT process starts with the deposition of an approximately 600 nm thick layer of aluminium (Al) onto the glass. The sample is then annealed at 600°C for 6 hours to allow Al to reduce silicon dioxide (SiO2) at the interface. Finally, the resulting layer of Al oxide and traces of Al and Si in this layer are removed with solutions of H3PO4 and HF/HNO3. A key feature of the AIT process is the experimentally observed fact that the reaction between Al and SiO2 is spatially non-uniform along the surface of the glass pane.
A focused ion beam image of one of these samples is shown on the right. The AIT glass texture has feature sizes approximately 1-2 µm wide and forms concave dimples in the glass surface. The combination of this surface morphology with convex features on the air side of the Si film enhances light scattering, by breaking up symmetry. The texture on the glass appears to be compatible with the SPC process.
The novel glass texturing method was recently presented at the Bangkok PV Conference (PVSEC-14) in Thailand [2] and has already created significant interest in the thin-film PV community.
Focused ion beam (FIB) microscope image of a poly-Si film made on AIT-textured glass. A trench is milled into the sample (lower part of image), revealing the cross section of the sample and the details of the glass texture. The glass is the black region in the trench.
[1] P.I. Widenborg and A.G. Aberle, Glass texturing
method, Australian Patent Provisional Application (7 April 2003).
International PCT patent application in progress.
[2] N. Chuangsuwanich, P.I. Widenborg, P. Campbell, and A.G. Aberle, “Light
trapping properties of thin silicon films on AIT-textured glass”, Tech.
Digest, 14th International Photovoltaic Science and Engineering Conference,
Bangkok, January, 2004, p. 325.