A novel low cost 25μm thin exfoliated monocrystalline Si solar cell technology

To achieve grid parity, photovoltaic (PV) technologies must reduce the production cost of PV modules to well below $1/Wp. In crystalline Si (c-Si) solar cells the cost of raw Si wafers is over 40% of the module cost. There is an industry wide push to reduce the active Si content of the cell through a combination of thinner wafers and increased cell efficiency. However, cell manufacturers are struggling to reduce the wafer thickness below 150μm as there are no economically viable technologies for manufacturing very thin Si wafers and such thin silicon wafers impose stringent handling requirements as wafer breakage and yield loss impact final module cost. In this paper, we demonstrate for the first time, a novel exfoliation technology capable of producing large area (6-in diameter) 25μm thin flexible mono c-Si foils that will dramatically change the cost structure and form factor of high efficiency-Si solar cells without the yield losses and handling issues that are a major problem for traditional thin Si wafers. An un-optimized single side heterojunction cell has been formed with a 25μm exfoliated c-Si foil, which shows an efficiency of 12.5%. The cell characteristics of a 25μm thin c-Si cell with intrinsic a-Si passivation will be presented in the paper. Simulations show that with optimized texturing of the foil and passivation, higher efficiencies (20%) can be attained. Depending on the starting wafer or ingot thickness a final cell cost of between $0.46/Wp to $0.50/Wp can be achieved compared to $1.1/Wp for today's commercial thick crystalline Si cells.