Current and lattice matched tandem solar cell
AssigneeThe United States of America as represented by the United States Department of Energy
InventorJerry M. Olson
Life of this patent
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Abstract
A multijunction (cascade) tandem photovoltaic solar cell device is fabricated of a Ga.sub.x In.sub.1-x P (0.505.ltoreq.X.ltoreq.0.515) top cell semiconductor lattice matched to a GaAs bottom cell semiconductor at a low-resistance heterojunction, preferably a p+/n+ heterojunction between the cells. The top and bottom cells are both lattice matched and current matched for high efficiency solar radiation conversion to electrical energy.
Claims13
A high-efficiency multijunction photovoltaic solar cell, comprising:
- a top semiconductor cell fabricated of GaInP.sub.2 with a light-sensitive n/p homojunction therein for absorbing higher energy photons;
- a bottom semiconductor cell fabricated of GaAs with a light-sensitive n/p homojunction therein for absorbing lower energy photons;
- a low-resistance attachment between said top cell and said bottom cell wherein said GaInP.sub.2 is lattice matched to said GaAs;
- and
- electrical contact means attached to opposite sides of said solar cell to conduct current away from and into said solar cell.
The method of converting solar radiation to electrical energy, comprising the steps of:
- directing the solar radiation into a first cell comprising Ga.sub.x In.sub.1-x P, where X=0.51.+-.0.005, with a band gap of about 1.9 eV, and having an n/p homojunction therein for absorbing and converting solar radiation of a wavelength of about 0.65 micron or less to electrical energy to produce about 1.3 to 1.4 V of open-circuit voltage;
- directing the unabsorbed solar radiation into a second cell comprising GaAs that is integrally grown and lattice connected with said Ga.sub.x In.sub.1-x P and having an n/p homojunction therein for absorbing and converting the remaining solar radiation of wavelength of about 0.85 micron or less to electrical energy to produce about 0.9 to 1.0 V of open-circuit voltage, which GaAs second cell is lattice-matched with said Ga.sub.x In.sub.1-x P first cell at a low resistance heterojunction;
- and
- connecting said first and second cells in series to an electrical load.
The method of converting solar radiation to electrical energy, comprising the steps of:
- directing solar radiation into a Ga.sub.x In.sub.1-x P/GaAs multijunction photovoltaic semiconductor device in which the Ga.sub.x In.sub.1-x P top cell is lattice matched at a p+/n+ heterojunction interface with the GaAs bottom cell and in which there is an n/p homojunction in the Ga.sub.x In.sub.1-x P top cell and another n/p homojunction in the GaAs bottom cell;
- absorbing higher energy solar radiation of 0.65 micron or less wavelengths in said top cell and converting it to electrical energy in said top cell while allowing lower energy solar radiation to pass through said top cell into said bottom cell;
- absorbing lower energy radiation of 0.85 micron or less wavelength and converting it in said bottom cell to electrical energy;
- and
- connecting said device to an electric load.
Dependencies are inferred from the claim text.