Yet another efficiency record has been established for mass-producible solar cells: 23.4%. The Fraunhofer Institute for Solar Energy Systems (ISE) from Germany succeeded to manufacture a single-crystal silicon solar cell of a thin p-type semiconductor layer residing on an n-type semiconductor substrate. The solar cell’s area is 2x2cm.
Until now, classic crystalline solar cells have been manufactured on p-type semiconductor substrates, with a thin n-type layer deposited on it. Reversing the order has been difficult because they needed a good sealant, since SiO2 and SiNx do not work well on p-type semiconductors. By using aluminum oxide (Al2O3) as a sealing material on the side that receives sunlight, it is now possible to manufacture relatively easy solar cells with n-type semiconductor as a substrate.
Added to the simplicity of manufacturing, n-type substrate solar cells have the big advantage that they are not as sensitive to impurities as are their p-type substrate sisters, and that means not only higher theoretical efficiency, but also a practical one.
The absolute solar efficiency obtained until now is 25%, achieved by a group led by prof. Martin Green from UNSW in Australia. Still, his solar cell “recipe” is not feasible, because it is difficult to be mass-produced. However, Fraunhofer’s cells may have a chance to get on the market soon enough.
