Graded band gap multi-junction solar energy cell

Claim 1

A solar cell comprising: a. a substrate layer of a crystalline material (compound) selected from the group consisting of compounds of group III-A-V-A elements (element compounds); and b. a monocrystalline layer on said substrate (i) composed of material selected from the group consisting of III-A-V-A compounds (element compounds) such that the composition of the monocrystalline layer is continuously changing and of the general form A 1-x A' x B 1-y B' y where A and A' are group IIIA elements selected from the group consisting of Al, Ga and In, B and B' are group VA elements selected from the group consisting of P, As and Sb, 0≦x≦1 and 0≦y≦1 whereby progressively narrower (continuously changing) band gaps are provided; (ii) suitably doped to produce a plurality of alternately active and inactive junctions; and (iii) having a p-region on one side and n-region on the other side of each inactive junction, and an active region about each active junction, said active region being bounded by an n-region and a p-region such that (a) in each p-region and in each n-region the flow of carriers is dominated by the region's concentration gradient; (b) (in each and every p-region and in n-region) the net current (density) throughout the cell is the same; (c) the electric field in each active region is much stronger than the electric fields in the p-region and n-region adjacent to it; and (d) the width (length) of each (each) region between active junctions substantially equals the diffusion length of the electrons and holes generated in (each) each said region.