German Institute Achieves 23.4% Efficiency With N-type Solar Cell

Sep 28, 2009
Tetsuo Nozawa, Nikkei Electronics
The newly-developed solar cell formed on a 4-inch wafer
The newly-developed solar cell formed on a 4-inch wafer
[Click to enlarge image]

Fraunhofer Institute for Solar Energy Systems (ISE) of Germany achieved an energy conversion efficiency of 23.4% with a single-crystal silicon solar cell made by forming a thin p-type semiconductor layer on an n-type semiconductor substrate.

Its cell area is 2 x 2cm. Fraunhofer ISE said that it is possible to mass-produce the solar cell, which is one of the most efficient crystalline silicon solar cells and could rival Sanyo and other companies' products.

Crystalline silicon solar cells based on n-type semiconductor substrates have a higher resistance to impurities than those based on p-type semiconductor substrates. Therefore, it is theoretically easier to enhance the energy conversion efficiency of the former solar cells.

However, most of the crystalline silicon solar cells developed so far are based on p-type semiconductor substrates. Specifically, they are made by forming a thin n-type semiconductor layer on a thick p-type semiconductor.

According to Fraunhofer ISE, sealing layer materials such as silicon oxide (SiO2) and silicon nitride (SiNx) do not work well on p-type semiconductors. Therefore, many kinds of crystalline silicon solar cells have been developed by forming an n-type semiconductor layer on a p-type semiconductor substrate and topping it with a SiO2 or SiNx layer.

This time, Fraunhofer ISE used aluminum oxide (Al2O3) as a sealing layer material on the side that receives sunlight. As a result, it became possible to develop a solar cell based on an n-type semiconductor substrate without having the problem of sealing.

The current highest conversion efficiency of crystalline silicon solar cell is 25%. And it was achieved by the group led by Martin Green, professor at the University of New South Wales (UNSW) in Australia. However, this solar cell is allegedly difficult to be mass-produced.