Cell structures with low-high heterojunction of c-Si and μc-Si: H under rear contact for improvement of efficiencies

Abstract For a remarkable improvement of conversion efficiencies of single-crystalline silicon (c-Si) solar cells, we have been investigating rear surface structures. The structure has a highly conductive boron (B) doped hydrogenated microcrystalline silicon (μc-Si:H) film with a wide optical bandgap between a p-type c-Si substrate and a rear contact instead of a heavily diffused layer. The conditions of depositing the μc-Si:H film were investigated. Both short-circuit current density ( J sc ) and open-circuit voltage ( V oc ) of the cell with the μc-Si:H film are much higher than those without the film. The V oc obtained was higher than 650 mV and the efficiency was 19.6% for a 5 cm × 5 cm cell. It is confirmed that a low-high heterojunction of the c-Si substrate and the μc-Si:H film is very effective in preventing minority carriers near the rear contact from recombining.