A single-crystal, monolithic, tandem, photovoltaic solar cell is described which includes (a) an InP substrate having upper and lower surfaces, (b) a first photoactive subcell on the upper surface of the InP substrate, and (c) a second photoactive subcell on the first subcell. The first photoactive subcell is GaInAsP of defined composition. The second subcell is InP. The two subcells are lattice matched. The solar cell can be provided as a two-terminal device or a three-terminal device.
A monolithic, tandem photovoltaic device is provided having an indium gallium arsenide tunnel junction lattice-matched to adjoining subcells and having high peak current densities and low electrical resistance. A method is provided for relatively low-temperature epitaxial growth of a subcell over the tunnel junction at temperatures which leave intact the desirable characteristics of the tunnel junction.
The incorporation of a pseudomorphic GaAsSb layer in a runnel diode structure affords a new degree of freedom in designing runnel junctions for p-n junction device interconnects. Previously only doping levels could be varied to control the tunneling properties. This invention uses the valence band alignment band of the GaAsSb with respect to the surrounding materials to greatly relax the doping requirements for tunneling.
A single-crystal, monolithic, tandem, photovoltaic solar cell is described which includes (a) an InP substrate having upper and lower surfaces, (b) a first photoactive subcell on the upper surface of the InP substrate, (c) a second photoactive subcell on the first subcell; and (d) an optically transparent prismatic cover layer over the second subcell. The first photoactive subcell is GaInAsP of defined composition. The second subcell is InP. The two subcells are lattice matched.
A monolithic, tandem photovoltaic device is provided having an indium phosphide tunnel junction lattice-matched to adjoining subcells and having high peak current densities and low electrical resistance. A method is provided for relatively low-temperature epitaxial growth of a tunnel junction and a subcell over the tunnel junction at temperatures which leave intact the desirable characteristics of the tunnel junction.
The efficiency of a two-junction (cascade) tandem photovoltaic device is improved by adjusting (decreasing) the top cell thickness to achieve current matching. An example of the invention was fabricated out of Ga.sub.0.52 In.sub.0.48 P and GaAs. Additional lattice-matched systems to which the invention pertains include Al.sub.x Ga.sub.1-x /GaAS (x= 0.3-0.4), GaAs/Ge and Ga.sub.y In.sub.l-y P/Ga.sub.y+0.5 In.sub.0.5-y As (0<y<5).
