Solar PV R&DProject Next Generation Crystalline Silicon on Glass Modules
The project developed a method for depositing silicon on glass using a simpler process than 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. The CSG technology was developed in Australia, commercialised in Germany but turned out to be too expensive to manufacture. To be commercially viable and competitive, the manufacturing cost of the CSG technology should be substantially lowered while its performance needs to be significantly improved. The project has 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; 2) to improve CSG cell performance by developing higher electronic quality silicon films using laser-induced liquid phase crystallisation. Both aims were successfully achieved as documented in the project milestone reports.
The project has established e-beam evaporation as a fast silicon film deposition process, with the rate 30 times higher than the plasma deposition. It takes only about 10 min to deposit 10 microns of silicon required for CSG solar cells as compared to about 5 hours by plasma deposition. Boron and phosphorous dopants are introduced with high precision from high temperature sources during evaporation. Evaporation is also inherently simpler and cheaper than plasma deposition because it uses solid inert materials as material sources instead of flammable and toxic gasses.
To become a solar cell material, the evaporated doped silicon has to be crystallised. Prior to the project, crystallisation was conducted in the solid phase producing poorly performing solar cells with high defect density, and the whole crystallisation process taking as long as 30 hrs. A novel process has been developed by the project using a line-shaped laser beam to melt the film and re-crystallise it into large low-defect grains. The laser crystallisation process takes less than a minute and produces a high electronic quality material. After implementing light-trapping specifically designed to improve light absorption in the evaporated film, the project demonstrated solar cells with the efficiency exceeding the previous CSG cells and approaching 13%. The new solar cells are named after the process as liquid-phased crystallised silicon on glass (LPCSG) cells.
The cost of ownership model developed by the project shows that the cost of electricity produced by the new LPCSG technology would be below the grid parity if the technology were to be commercialised.