Gallium arsenide solar cells are very efficient but are expensive. Their efficiency reaches as high as 29% in laboratory and about 20% in real world. Multi junction or tandem solar cells can show even up to 40.9% efficiency. These solar cells are formed by depositing several thin layers of single crystal layers on top of the substrate. The layers are doped oppositely to conduct electricity. Due to heat resistivity and high absorption they have found extensive applications in spacecrafts.