20.1%-Efficient crystalline silicon solar cell with amorphous silicon rear-surface passivation

We have developed a crystalline silicon solar cell with amorphous silicon (a-Si:H) rear-surface passivation based on a simple process. The a-Si:H layer is deposited at 225 degrees C by plasma-enhanced chemical vapor deposition. An aluminum grid is evaporated onto the a-Si:H-passivated rear. The base contacts are formed by COSIMA (contact formation to a-Si:H passivated wafers by means of annealing) when subsequently depositing the front silicon nitride layer at 325 degrees C. The a-Si:H underneath the aluminum fingers dissolves completely within the aluminum and an ohmic contact to the base is formed. This contacting scheme results in a very low contact resistance of 3.5 +/- 0.2 m Omega cm(2) on low-resistivity (0.5 Omega cm) p-type silicon, which is below that obtained for conventional Al/Si contacts. We achieve an independently confirmed energy conversion efficiency of 20.1% under one-sun standard testing conditions for a 4 cm(2) large cell. Measurements of the internal quantum efficiency show an improved rear surface passivation compared with reference cells with a silicon nitride rear passivation. Copyright (c) 2005 John Wiley & Sons, Ltd.