Gallium arsenide solar cells are marked by high efficiency and high price. Due to these reasons, they have found most of their applications where such a high efficiency is required and the budget of the project allows their use.
Aerospace industry is the most important industry where these cells are being used extensively.
Efficiency of Gallium Arsenide Solar cells
These cells have efficiency as high as 29% during laboratory testing. But, since the conditions are different in real world, their efficiency drops somewhat but they can still show an efficiency of 20%. The greater efficiency in laboratory is mainly because a concentrated light source is used to calculate the efficiency there.