R&D toward a 15+% efficiency solar cell manufacturing line for EFG silicon wafers

High growth rates used in multicrystalline silicon wafer production result in defects and deficiencies in bulk lifetime. This imposes a challenge for solar cell processing to find methods which recover this lifetime. We report here on R&D on a 4 MW EFG Si manufacturing line which has addressed this issue. Efforts in wafer and cell fabrication areas included: obtaining consistent graphite purification methods to improve as-grown wafer bulk quality, and optimization of bulk resistivity, SiN AR deposition, and lastly, metalization firing with respect to sheet resistivity and Al layer thickness. We discuss application of statistical process control methodology and design of experiment techniques used in this optimization. This work resulted in achieving greater than 14% average production cell efficiencies on 10×10 cm EFG wafers, and individual cell lots with efficiencies as high as 14.7%, with over one-third of the cells exceeding 15%. Lastly, we discuss current barriers to attaining overall averages of 15%