Photovoltaic cell with variable band gap

A Monolithic photovoltaic cell is proposed. Said cell comprises at least one junction. Each one of said at least one junction comprises a base formed by a doped semiconductor material of a first conductivity type and an emitter formed by a doped semiconductor material of a second conductivity type opposed to the first. Said emitter is stacked on the base according to a first direction. The semiconductor material of the base and/or of the emitter of at least one of said at least one junction is a semiconductor material formed by a compound of at least one first element and a second element. The band gap and the lattice constant of said semiconductor material of the base and/or of the emitter depend on the concentration of said first element in said compound with respect to said second element. Said concentration of the first element in said compound with respect to the second element is not uniform along said first direction, being equal to a first value at a lower portion of said base and/or emitter and being equal to a second value lower than the first value at an upper portion of said base and/or emitter. Said upper portion is above said lower portion according to the first direction.