Mass Production Test of Solar Cells and Modules Made of 100% UMG Silicon. 20.76% Record Efficiency

For more than 15 years FerroAtlantica (now Ferroglobe) has been developing a method of silicon purification to obtain Upgraded Metallurgical Grade Silicon (UMG-Si) for PV solar application without blending. After many improvements and optimizations, the final process has clearly demonstrated its validity in terms of quality and costs. In this paper the authors present new results stemming from a first mass-production campaign and a detailed description of the purification process that results in the tested UMG-Si. The subsequent steps in the value chain for the wafer, cell and module manufacturing are also described. Two independent companies, among the Tier-1 solar cells producers, were selected for the industrial test, each using a different solar cell technology: Al-BSF and black silicon + PERC. Cells and modules were manufactured in conventional production lines and their performances compared to those obtained with standard polysilicon wafers produced in the same lines and periods. Thus, for Al-BSF technology, the average efficiency of solar cells obtained with UMG-Si was (18.4 ± 0.4)% compared to 18.49% obtained with polysilicon-made wafers. In the case of black silicon + PERC, the average efficiency obtained with UMG-Si was (20.1 ± 0.6)%, compared to 20.41% for polysilicon multicrystalline wafers.

Study of the Boron Distribution and Microstructure of Solidified Al-Si Alloy During the Process of Silicon Purification

The Al-Si melts that contain different silicon contents were solidified with a series of cooling rates, and the boron contents in primary silicon phases and eutectic silicon phases were measured and discussed. The results indicate that the boron content in the eutectic silicon phases is higher than that in the primary silicon phases when the cooling rate is constant. When the cooling rate decreases, the boron content in the primary silicon phases decreases, but the boron content in the eutectic silicon phases increases. The microstructure observations of solidified ingots show that there is an interface transition layer beside the primary silicon phase, and the average width of the interface transition layer increases with decreasing cooling rate.