Zn as the protective layer for Cu electrode in wafer-Si solar cells

Zn is proposed as the protective layer for the Cu electrode in wafer-Si solar cells to replace today´s Ag front electrode. Zn provides a lower material cost, a lower resistivity and more abundant material reserve than Sn. The thermal stability of the Zn/Cu/Ni stack is examined by annealing it in air and the Zn/Cu/Ni stack is advantageous over the Sn/Cu/Ni stack in thermal stability. This is attributed to the better coverage of electroplated Zn on Cu and the higher melting point of Zn over Sn. The sheet resistance of the Zn/Cu/Ni stack is also lower than the Sn/Cu/Ni stack due to the lower resistivity of Zn. XRD measurements before and after annealing confirms that the increased sheet resistance upon annealing is due to oxidation and alloying of the Cu layer. For solderability, a Sn/Zn/Cu/Ni stack with reduced Sn thickness is demonstrated by sequential electroplating.