AbstractsEngineering

Intermediate Layers for Laser-Crystallised Thin-Film Silicon Solar Cells on Glass

by Jonathon Dore




Institution: University of New South Wales
Department: Photovoltaics & Renewable Energy Engineering
Year: 2014
Keywords: Laser; Solar Cell; Thin Film; Polycrystalline; Silicon; LPCSG
Record ID: 1051388
Full text PDF: http://handle.unsw.edu.au/1959.4/53928


Abstract

Liquid phase crystallised silicon on glass (LPCSG) is a promising solar cell technology using high-quality polycrystalline silicon thin films to produce low-cost solar modules. In this work, a line-focused continuous-wave diode laser is used to melt and recrystallise 10 micron thick silicon films on borosilicate glass. Different intermediate layers between the glass and the silicon are assessed for their suitability for such cells. SiOx, SiNx and SiCx are tested either as single films or in multilayer stacks with regard to optical properties as an anti-reflection coating (ARC), wettability, silicon crystal quality, diffusion properties and device performance. SiOx is found to be optically indistinguishable from the glass, providing no anti-reflective benefit. SiCx is limited to thin (~20 nm) films due to parasitic absorbance. Combining thin SiCx with a thin Si-side SiOx layer creates an acceptable ARC. SiNx provides the best ARC. SiCx layers, either alone or in stacks with SiOx, are found to provide the best wettability, allowing the largest range of laser parameters for crystallisation without silicon dewetting. SiOx and SiNx allow a smaller, but sufficient process range. Large crystal grains, several millimetres in length, are formed after crystallisation with all intermediate layer options. The density of twin grain-boundaries is found to be dependent upon intermediate layer class, with single layer SiOx causing the lowest density, followed by SiCx-based layers, then SiNx-based layers. SiOx is found to be the best barrier against boron diffusion from the borosilicate glass, limiting unintentional doping to <1e16 cm-3. Diffusion of nitrogen and carbon into the silicon from SiNx and SiCx layers occurs, causing concentrations of up to 1e19 cm-3. Iron concentration up to 1e17 cm- 3 is found in several silicon films after crystallisation, regardless of intermediate layer. Solar cell efficiency remains below 4 % when SiNx or SiCx intermediate layers are in contact with the silicon. Inserting a thin (~10-20 nm) Si-side SiOx layer improves efficiency to >7 % for otherwise similar cells. Efficiency up to 11.7 % is measured for a cell with a SiOx/SiNx/SiOx intermediate layer stack. A subsequent degradation is found to reduce this to ~10 %