NOVELTY - The solar cell stack comprises multiple semiconductor solar cells of germanium (Ge) and/or Ge compound and/or an III-V compound. Each of the solar cells includes a P/N junction. A first solar cell part (20) has a first lattice constant, a top and a bottom, and includes a first semiconductor solar cell. A second solar cell part (30) has a second lattice constant, a top and a bottom, and a second semiconductor solar cell. The first and second solar cell parts are arranged one on top of the other with frictional engagement.    USE - Used as a solar cell stack.    ADVANTAGE - The solar cell stack can be easily and economically manufactured with high reliability.    DETAILED DESCRIPTION - The solar cell stack comprises multiple semiconductor solar cells of germanium (Ge) and/or Ge compound and/or an III-V compound. Each of the solar cells includes a P/N junction. A first solar cell part (20) has a first lattice constant, a top and a bottom, and includes a first semiconductor solar cell. A second solar cell part (30) has a second lattice constant, a top and a bottom, and a second semiconductor solar cell. The first and second solar cell parts are arranged one on top of the other with frictional engagement. An abrupt difference between the first and second lattice constants is formed between the first and second solar cell parts. The difference between the lattice constants is 0.5%. The first solar cell part and/or the second solar cell part comprises a further semiconductor solar cell and a metamorphic intermediate layer. The metamorphic intermediate layer comprises a first layer thickness, and changes the lattice constant by 0.5% along the extent of the thickness of the intermediate layer. An interface (35) is formed between the bottom of the first solar cell part and the top of the second solar cell part with the abrupt difference. The interface comprises an amorphous layer having a layer thickness of less than 20 nm. The bottom of the first solar cell part has a first chemical compound, and the top of the second solar cell part comprises a second chemical compound. The first and second compounds differ in a chemical element. The solar cell parts comprise lattice-matched layers, are connected to each other by a semiconductor bonding and by wafer bonding. The first solar cell part is mechanically connected to the second solar cell part using a fastening device such as a clamping device. The first solar cell part and/or the second solar cell part comprises a triple-or quad solar cell and metamorphic intermediate layers. The semiconductor solar cells have a first band gap of 1.9-2.1 eV, a second band gap of 1.6-1.9 eV, a third band gap of 1.4-1.6, a fourth band gap of 1-1.5 eV, a fifth band gap of 0.8-1.1 eV, and a sixth band gap of 0.6-0.7 eV.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross-sectional view of a solar cell stack.    First solar cell (20)    Second solar cell part (30)    Interface. (35)