The p recombination layer in tunnel junctions for micromorph tandem solar cells

A new tunnel recombination junction is fabricated for n—i—p type micromorph tandem solar cells. We insert a thin heavily doped hydrogenated amorphous silicon (a-Si:H) p⁺ recombination layer between the n a-Si:H and the p hydrogenated nanocrystalline silicon (nc-Si:H) layers to improve the performance of the n—i—p tandem solar cells. The effects of the boron doping gas ratio and the deposition time of the p-a-Si:H recombination layer on the tunnel recombination junctions have been investigated. The current-voltage characteristic of the tunnel recombination junction shows a nearly ohmic characteristic, and the resistance of the tunnel recombination junction can be as low as 1.5 Ω·cm² by using the optimized p-a-Si:H recombination layer. We obtain tandem solar cells with open circuit voltage V_oc= 1.4 V, which is nearly the sum of the V_ocs of the two corresponding single cells, indicating no V_oc losses at the tunnel recombination junction.