Bow reducing factors for thin screenprinted MC-Si solar cells with Al BSF

Silicon solar cell costs could be strongly reduced by the use of thinner wafers. However, thin wafers are susceptible to bowing caused by the influence of the metallisations on the front and rear side. Excessively bowed wafers lead to unacceptable yield losses during module construction. Screen printed aluminium paste is the major contributor to bowing which increases with decreasing wafer thickness. One barrier to using thinner wafers is the lack of an aluminium paste that combines good doping conditions for the BSF, good ohmic contact properties with a composition that has low bowing tendencies. In this work, we studied the effect of Al print thickness on electrical and mechanical performance of new aluminium pastes, developed by DuPont, using 200 μm thick 12.5×12.5 cm wafers. The influence of aluminium paste composition, firing conditions and silver front side was also studied.