High-speed Fabrication of Laser Doping Selective Emitter Solar Cells Using 532nm Continuous Wave (cw) and Modelocked Quasi-cw Laser Sources

In recent years, laser doping of selective emitters (LDSE) has demonstrated great promise for improving c-Si solar cell performance with the potential for low cost of adaptation. Absolute cell efficiency improvement of 1 – 2 % is seen with a process pioneered at the University of New South Wales which couples narrow-line LDSE processing with a self-aligning, light-induced plating (LIP) metallization process. To help transfer this technology to the manufacturing floor, it is important to find and characterize the ideal laser source for LDSE processing. Current laser sources that may be considered include continuous wave (CW) and modelocked (ML) quasi-CW laser sources. The output to these lasers make them well-suited for localized heating and melting of materials, and they can be built at various wavelengths, such as near infrared (NIR) at 1064 nm, green at 532 nm, and ultraviolet (UV) at 355 nm. While both CW and ML lasers might be good choices, they are vastly different in both their optical radiation output profile and their technological architectures. These differences could have important ramifications for manufacturability of LDSE solar cells. As such, we have in this work characterized both CW and modelocked laser technologies for LDSE processing. With optical emission at the 532-nm wavelength, LDSE features were created at scan speeds of 2 to 12 m/s and power levels from 12 – 15W. LIP metallization was used for final cell fabrication. Efficiencies of 17.4 – 18.4% and fill factors from 77 – 79% are typically achieved. LDSE cells fabricated with 355-nm ML laser source were also compared. Theoretical considerations with regard to the wavelength and laser type are explored; and the suitability of the various laser sources for large-scale production is discussed.