Maximising Minority Carrier Lifetime in High Efficiency Screen Printed Silicon BSF Cells

A theoretical model was used to predict the performance of n+pp+ solar cells as the wafer thickness was reduced. Solar cells were made using aluminium and boron to produce the BSF in wafer thickness from 350 to 200 microns and resistivities from 1 to 10 ohm cm. The boron based cells gave good agreement with the model but the aluminium p+ cells did not. The model was used to demonstrate the effect of increasing minority carrier diffusion length in the cell. The minority carrier diffusion length of the aluminium p+ cells was measured by EBIC and spectral response. A large increase in diffusion length was noted and the gettering action of the aluminium was confirmed by SIMS analysis. High efficiency cells were made in the optimum design.