Hybrid tandem solar cells with improved tunnel junction structures
Tandem solar cells comprising two or more solar cells connected in a solar cell stack via pn diode tunnel junctions and methods for fabricating the tandem solar cells using epitaxial lift off and transfer printing are provided. The tandem solar cells have improved tunnel junction structures comprising a current tunneling layer integrated between the p and n layers of the pn diode tunnel junction that connects the solar cells.
1. A tandem solar cell comprising:
(a) a first solar cell comprising: a first back surface field comprising a p- or n-type doped semiconductor; a first base comprising a p- or n-type doped semiconductor; and a first emitter comprising an n- or p-type doped semiconductor, wherein the dopant type of the first back surface field and the first base is the opposite of the dopant type of the first emitter;
(b) a second solar cell stacked atop the first solar cell, wherein the second solar cell absorbs a different range of wavelengths than the first solar cell, the second solar cell comprising: a second back surface field comprising an p- or n-type doped semiconductor; a second base comprising a p- or n-type doped semiconductor; and a second emitter comprising an n- or p-type doped semiconductor, wherein the dopant type of the second back surface field and the second base is the opposite of the dopant type of the second emitter; and
(c) a pn diode tunnel junction connecting the first solar cell to the second solar cell, the pn diode tunnel junction comprising: a first tunnel junction layer comprising a first single-crystalline n- or p-type doped semiconductor on the upper surface of the first solar cell; a second tunnel junction layer comprising a second single-crystalline p- or n-type doped semiconductor on the lower surface of the second solar cell, wherein the first single-crystalline n- or p-type doped semiconductor is different than the second single-crystalline p- or n-type doped semiconductor; and a current tunneling layer disposed between and in contact with the first and second tunnel junction layers;
wherein the current tunneling layer comprises an inorganic material having a bandgap that is wider than the bandgaps of the semiconductors of the first and second tunnel junction layers.
2. The tandem solar cell of claim 1 , wherein the inorganic material does not consist of a native oxide of the semiconductors of first or second tunnel junction layers.
3. The tandem solar cell of claim 1 , wherein the inorganic material of the current tunneling layer is aluminum oxide.
4. The tandem solar cell of claim 1 , wherein the doped semiconductors of the first back surface field of the first solar cell, the first base of the first solar cell, the first emitter of the first solar cell and the first tunnel junction layer comprise a doped Group IV semiconductor; and the doped semiconductors of the second back surface field of the second solar cell, the second base of the second solar cell, the second emitter of the second solar cell and the second tunnel junction layer comprise a doped Group III-V semiconductor.
5. The tandem solar cell of claim 4 , wherein the inorganic material does not consist of a native oxide of the semiconductors of first or second tunnel junction layers.
6. The tandem solar cell of claim 5 , wherein the inorganic material of the current tunneling layer comprises aluminum oxide.
7. The tandem solar cell of claim 4 , wherein the doped Group IV semiconductors of the first back surface field and the first base of the first solar cell is p-type doped; the doped Group IV semiconductors of the first emitter of the first solar cell and the first tunnel junction layer are n-type doped; the doped Group III-V semiconductors of the second tunnel junction, the second back surface field and the second base of the second solar cell are p-type doped; and the Group III-V semiconductor of the second emitter of the second solar cell is n-type doped.
8. The tandem solar cell of claim 7 , wherein the inorganic material does not consist of a native oxide of the semiconductors of first or second tunnel junction layers.
9. The tandem solar cell of claim 8 , wherein the inorganic material of the current tunneling layer comprises aluminum oxide.
10. The tandem solar cell of claim 7 , wherein the Group IV semiconductor of the first base and first emitter of the first solar cell and the first tunnel junction layer is silicon; the Group III-V semiconductor of the second base and second emitter of the second solar cell is an AlGaAs semiconductor; and the Group III-V semiconductor of the second tunnel junction layer is GaAs.
11. The tandem solar cell of claim 10 , wherein the inorganic material does not consist of a native oxide of the semiconductors of first or second tunnel junction layers.
12. The tandem solar cell of claim 11 , wherein the inorganic material of the current tunneling layer comprises aluminum oxide.
13. The tandem solar cell of claim 10 , wherein the AlGaAs of the second base and second emitter of the second solar cell is Al 0.3 Ga 0.7 As.
14. The tandem solar cell of claim 13 , wherein the inorganic material does not consist of a native oxide of the semiconductors of first or second tunnel junction layers.
15. The tandem solar cell of claim 14 , wherein the inorganic material of the current tunneling layer comprises aluminum oxide.
16. The tandem solar cell of claim 15 , wherein the second solar cell further comprises a window layer comprising n-type doped GaAs disposed over the second emitter and one or more electrically conductive contact pads on the window; and the first solar cell further comprises one or more electrically conductive contact pads on the first back surface field.