A solar cell stack, having a first semiconductor solar cell having a p-n junction made of a first material with a first lattice constant, and a second semiconductor solar cell having a p-n junction made of a second material with a second lattice constant, and the first lattice constant being at least 0.008 Å smaller than the second lattice constant, and a metamorphic buffer, the metamorphic buffer being formed between the first semiconductor solar cell and the second semiconductor solar cell, and the metamorphic buffer including a series of three layers, and the lattice constant increasing in a series in the direction of the semiconductor solar cell, and the lattice constants of the layers of the metamorphic buffer being bigger than the first lattice constant, two layers of the buffer having a doping, and the difference in the dopant concentration between the two layers being greater than 4E17 cm−3.