Development and comparison of small and large area boron doped solar cells in n-type and p-type Cz-Si

The first step to introduce an evolutionary approach is the development in the laboratory scale and, then, in pilot plant and mass production. Boron diffusion forms the emitter in n-type substrates and the back surface field (BSF) in p-type silicon wafers. N-type Cz-Si solar cells have been investigated due to the potential to produce high efficiency solar cells and boron BSF may provide a better passivation than aluminum BSF in p-type wafers. The goal of this paper is to present the development and comparison of small and large area solar cells, processed in Czochralski silicon wafers by using spin-on dopant to obtain the boron emitter in n-type Si substrates and the boron BSF in p-type ones. The average efficiency of boron emitter and BSF cells was of around 15.0 % and 13.4 % for small and large area solar cells, independently of the substrate type. The reduction of the efficiency is due to the short-circuit current density that falls of around 5 mA/cm² when the area is enlarged. The low fill factor obtained in p⁺nn⁺ cells is due to the high resistivity of Ag/Al paste deposited in the boron emitter cells and the soldering of the Ag/Sn/Cu ribbon increased this parameter from 0.70 to 0.75 in large area cells.