Series resistance in double-polysilicon-contacted silicon solar cells

Series resistance values between 0.38 and 0.5 Rcm² have been obtained in solar cells contacted with polysilicon to both surfaces. 2.6% of the front area is contacted with a silicon/heavily doped polysilicon/metal structure to replace the conventional metal contact. The same technology has been applied to the solar cell backs to replace conventional back-surface-field (BSF) structure. The devices were fabricated in 4" wafers, and a VLSI polysilicon emitter technology was applied to fabricate polysilicon contacts. The polysilicon-silicon interface was produced using either an HF etch or RCA clean before polysilicon deposition, and half of the wafers were implanted with fluorine to assess the passivating effects on the polysilicon-silicon interface. The drive-in time of the impurities from the polysilicon into the silicon was also varied. The main results are that the series resistance is generally lower in fluorinated samples, both HF and RCA. The contribution to the total series resistance of the back side structure is evaluated by subtracting the front contributions independently measured