The invention relates to a multi-junction solar cell comprising at least two sub-cells based on silicon and at least one material other than silicon, wherein a first sub-cell is designed to use photons in a spectral region of a shorter wavelength than a spectral region of a longer wavelength of a second sub-cell, the second sub-cell being based on silicon and the first sub-cell being based on a material which has a larger band gap than silicon, wherein the first sub-cell and the second sub-cell are designed as a monolithic unit consisting of a layer stack, and wherein the first sub-cell and the second sub-cell are electrically connected to one another in series by means of a tunnel diode, such that the tandem solar cell is equipped with two terminals, wherein the tunnel diode has a tunnel diode n layer and a tunnel diode p layer. The problem addressed is that of proposing a multi-junction solar cell of simple construction. The problem is solved by multi-junction solar cells in which the tunnel diode n layer and/or the tunnel diode p layer is/are silicon-based layer(s).