Record efficiencies above 21% for MIS-contacted diffused junction silicon solar cells

High-efficiency solar cells obtained by a simple cost-effective manufacturing process are required for a drastic reduction of the costs of solar electricity. In this paper an improved and yet simple processing sequence for highly efficient MIS-contacted diffused n(+)p junction (MIS-n(+)p) silicon solar cells is presented. The process is characterised by: (i) formation of a metal-insulator-semiconductor (MIS) contact on an n(+)-diffused emitter, (ii) aluminium metallisation for front and rear electrodes, and (iii) low-temperature surface passivation by PECVD silicon nitride. For MIS-n(+)p solar cells with the front grid defined by Al evaporation through a shadow mask efficiencies of up to 20.6% have been obtained. Furthermore, mask-free metallised cells with a mechanically grooved front surface have been fabricated. These cells have reached an confirmed efficiency of 21.1%, the highest value to date reported for MIS-n(+)p silicon solar cells.