TECHNOLOGY FOCUS - ELECTRONICS - Preferred Solar Cell: In the multi-junction solar cell, the second layers are formed of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 5). The N constituent of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) provides a lattice constant for offsetting strain caused by the GaAsxN1-x (0 less than x less than 1). The band gap energy of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) and the band gap energy of GaAsxN1-x (0 less than x less than 1) form a multi quantum well structure, the band gap energy of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) being higher than the band gap energy of GaAsxN1-x (0 less than x less than 1). The band gap energy of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) and the band gap energy of GaAsxN1-x (0 less than x less than 1) form a multi quantum well structure, the band gap energy of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) being lower than the band gap energy of GaAsxN1-x (0 less than x less than 1). The GaAsN sub cell has a thickness of 0.1-5 mu m. The set of sub cells is four or more. The set of sub cells include a first sub cell formed of germanium (Ge), and the GaAsN sub cell is a second sub cell disposed on the first sub cell. The multi-junction solar cell further comprises: a sub cell formed of InxGa1-xAs (0 less than x less than 1), InxGa1-xP (0 less than x less than 1), In1-x-yGaxAlyP (0 less than or equal to x less than 1, 0 less than or equal to y less than 1, 0 less than or equal to x+y less than 1), AlxGa1-xAs (0 less than x less than or equal to 1), or combinations on the GaAsN sub cell; a third sub cell formed of InxGa1-xAs (0 less than x less than 1) on the GaAsN sub cell; and a fourth sub cell formed of InxGa1-xP (0 less than x less than 1) on the third sub cell. The N constituent of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) provides a lattice constant for offsetting strain caused by the GaAsxN1-x (0 less than x less than 1). The band gap energy of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) and the band gap energy of GaAsxN1-x (0 less than x less than 1) form a multi quantum well structure, the band gap energy of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) being higher than the band gap energy of GaAsxN1-x (0 less than x less than or equal to 1). Moreover, the band gap energy of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) and the band gap energy of GaAsxN1-x (0 less than x less than 1) form a multi quantum well structure, the band gap energy of GaxIn1-xNyAs1-y (0 less than x less than 1, 0 less than or equal to y less than 1) being lower than the band gap energy of GaAsxN1-x (0 less than x less than 1). The GaAsN sub cell has a p-n junction structure. The multi-junction solar cell as well comprises: cladding layers formed of gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), or indium gallium aluminum phosphide (InGaAlP) on an uppermost layer and a lowermost layer of the GaAsN sub cell.