A photovoltaic cell, comprising: a first p-n junction layer having a first energy band gap between a valence band and a conduction band of said first p-n junction layer, wherein the first p-n- junction layer comprises an intrinsic layer between the n-doped and the p-doped layers (24, 26) of the first p-n- junction layer; a second p-n junction layer having a second energy band gap between a valence band and a conduction band of said second p-n junction layer, wherein the second p-n junction layer comprises an intrinsic layer between the n-doped and the p-doped layers (32, 34) of the second p-n junction layer, said first energy band gap being greater than said second energy band gap; a tunnel junction layer positioned between said first and second p-n junctions; a plurality of quantum dots, which are nanocrystal structures formed of semiconductor material; a first electrical conductor layer contiguous with said first p-n junction layer; and a second electrical conductor layer contiguous with said second p-n junction layer, characterized in that the plurality of quantum dots has a distribution confined to a surface of an n-doped layer and a p-doped layer of at least said first p-n layer, wherein said quantum dots are disbursed throughout the n-doped and p-doped layer at a volume density up to 10 21 cm -3 or an areal density from about 10 8 cm -2 to about 10 11 cm -2 wherein the size of the quantum dots, their density and spacing from one another are coordinated so as to provide effective quantum mechanical tunneling of charge carriers energized by incident photons to the conductor layer; wherein the quantum dots are distributed substantially at the surface of the n-doped and p-doped layers(24, 26) or throughout the volume of the layers in a three dimensional array. comprising: a first p-n junction layer having a first energy band gap between a valence band and a conduction band of said first p-n junction layer, wherein the first p-n- junction layer comprises an intrinsic layer between the n-doped and the p-doped layers (24, 26) of the first p-n- junction layer; a second p-n junction layer having a second energy band gap between a valence band and a conduction band of said second p-n junction layer, wherein the second p-n junction layer comprises an intrinsic layer between the n-doped and the p-doped layers (32, 34) of the second p-n junction layer, said first energy band gap being greater than said second energy band gap; a tunnel junction layer positioned between said first and second p-n junctions; a plurality of quantum dots, which are nanocrystal structures formed of semiconductor material; a first electrical conductor layer contiguous with said first p-n junction layer; and a second electrical conductor layer contiguous with said second p-n junction layer, characterized in that the plurality of quantum dots has a distribution confined to a surface of an n-doped layer and a p-doped layer of at least said first p-n layer, wherein said quantum dots are disbursed throughout the n-doped and p-doped layer at a volume density up to 10 21 cm -3 or an areal density from about 10 8 cm -2 to about 10 11 cm -2 wherein the size of the quantum dots, their density and spacing from one another are coordinated so as to provide effective quantum mechanical tunneling of charge carriers energized by incident photons to the conductor layer; wherein the quantum dots are distributed substantially at the surface of the n-doped and p-doped layers(24, 26) or throughout the volume of the layers in a three dimensional array.