This project aimed to increase the efficiency of crystalline silicon on glass thin-film solar cells beyond the current world record and to reduce the manufacturing costs by developing new breakthrough approaches to the cell fabrication.
It is not possible to produce a high quality solar cell material when the silicon is in direct contact with glass for a number of reasons:
- Wetting between liquid silicon and glass is poor causing film delamination during melting; impurities from glass diffuse into silicon producing electronic defects
- the reflection from the silicon glass interface is very high
- the carrier recombination at the silicon-glass interface is very high too.
To solve these problems, an intermediate layer between glass and the silicon is required which possesses the following properties:
- high thermal stability above silicon melting point
- good wetting of molten silicon
- low absorption and high antireflection
- good impurity diffusion barrier, and
- good interface passivation.
Increasing solar cell efficiency and reducing its cost will make solar electricity more affordable in Australia.
The project involved the development of a method for depositing silicon on the glass with a much simpler process than the conventional plasma-enhanced chemical vapour deposition. Thin-film Crystalline Silicon on Glass (CSG) is a new photovoltaic (PV) technology that uses a very thin layer of a silicon material to fabricate solar cells supported by a cheap transparent glass substrate. It has the same material benefits as the proven mature silicon wafer-based PV technologies while consuming only a small fraction of the expensive material.
To be commercially viable and competitive, the manufacturing cost of the CSG technology needed to be substantially lowered while its performance needed to be significantly improved. The project had two major aims:
1) to reduce the manufacturing cost by replacing the currently standard silicon film fabrication by slow and expensive plasma deposition with much faster and cheaper electron beam (e-beam) evaporation; and
2) to improve CSG cell performance by developing higher electronic quality silicon films using laser-induced liquid-phase crystallisation.
The new solar cell fabrication technology delivered efficiency and cost advantages over other thin film silicon solar cells.
Both of the projects two aims were successfully achieved. The project has established e-beam evaporation as a high rate commercially viable silicon film deposition process for the solar cell application. The project also introduced novel line laser crystallisation for creating a high electronic quality silicon material. The solar cells fabricated by evaporation and laser crystallisation perform better than old CSG cells and are cheaper to manufacture.
A cost of ownership model was created to estimate the manufacturability of the new technology which demonstrated that it can achieve the grid parity with conventional electricity sources. The project research results have been published in 17 peer reviewed journal papers and 15 conference papers.