TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Cell: In the solar cell, the group IV layer and the nucleation layer are in an arrangement defined by having substantially only group III elements of the nucleation layer positioned on the surface of the group IV layer to form a group III monolayer, the arrangement further defined by having substantially only group V elements of the nucleation layer positioned on the group III monolayer, the arrangement to prevent a formation of anti-phase domain defects in the first III-V compound layer, to control a diffusion of group V elements from the first III-V compound layer into the group IV layer, and to control a diffusion of group IV elements from the group IV layer into the first III-V compound layer. The group IV layer and the nucleation layer are in an arrangement defined by having substantially only group V elements of the nucleation layer positioned on the surface of the group IV layer to form a group V monolayer, the arrangement further defined by having substantially only group III elements of the nucleation layer positioned on the group V monolayer, the arrangement to prevent a formation of anti-phase domain defects in the first III-V compound layer, to control a diffusion of group V elements from the first III-V compound layer into the group IV layer, and to control a diffusion of group IV elements from the group IV layer into the first III-V compound layer. The nucleation layer covers at least 25% of the surface of the group IV layer. Also, at least one of the nucleation layer and the at least one additional layer is a pseudomorphic layer. The nucleation layer is a strained layer. The nucleation layer further includes at least one of gallium (Ga) and indium (In) as a group III element. The additional layer includes at least one of gallium indium phosphide (GaInP), aluminum indium phosphide (AlInP), and aluminum gallium indium phosphide (AlGaInP). The additional layer includes an indium gallium arsenide (InGaAs) layer. The group IV layer is one of a p-type layer, an n-type layer and an undoped layer. The group IV layer is selected from a germanium (Ge) layer, a silicon (Si) layer, a Si-Ge and a silicon carbide (SiC) layer. The group IV layer is a group IV substrate. Moreover, at least one of the nucleation layer and the at least one additional layer is formed by an epitaxial growth process. The average thickness of the nucleation layer is at least 0.25 monolayer. Alternatively, the multi-junction solar cell comprises: a group IV layer having a surface defined by a (100), (010) or (001) plane inclined, at an angle ranging from 0-20 degrees , towards a (111) plane of the group IV layer, the (100), (010) or (001) plane containing group IV elements spaced-apart by a group IV layer in-plane lattice parameter; a nucleation layer formed on the surface of the group IV layer, the nucleation layer including a III-V compound, a thickness of the nucleation being comprised between 0.25 monolayer of the III-V compound and one monolayer of the III-V compound; and at least one additional layer containing a III-V compound, the at least one additional layer being formed on the nucleation layer, the at least one additional layer and the nucleation layer each having, in a direction substantially parallel to the (100), (010) or (001) plane, a lattice parameter substantially equal to the group IV layer in-plane lattice parameter, the solar cell including a first p-n junction formed in the group IV layer and a second p-n junction formed in the at least one additional layer. In a second alternative case, the multi-junction solar cell comprises: a group IV layer having a surface defined by a plane, the plane containing group IV elements spaced-apart by a group IV layer in-plane lattice parameter, the group IV layer having a p-n junction formed in it; a nucleation layer formed on the surface of the group IV layer, the nucleation layer having a nucleation layer thickness, the nucleation layer including a III-V compound having at least Al as a group III element and at least one of As, N and Sb as a group V element; and at least one additional layer containing a III-V compound, the at least one additional layer being formed on the nucleation layer, the at least one additional layer having, in a direction substantially parallel to the plane of the group IV layer, a lattice parameter substantially equal to the group IV layer in-plane lattice parameter, the p-n junction having a p-doped base and an n-doped emitter, the n-doped emitter being defined by at least two n-type dopants, each n-type dopant having associated thereto a respective concentration that varies as a function of distance from the group IV surface, one of the n-type dopants being a group V element, from the at least one additional layer, that has diffused from the at least one additional layer into the group IV layer, another of the n-type dopants being a group V element, from the nucleation layer, that has diffused from the nucleation layer into the group IV layer. 18. The solar cell of claim 17 where each concentration associated with each of the n-type dopant is a function of the nucleation layer thickness.