MULTI-JUNCTION SOLAR CELL WITH DILUTE NITRIDE SUB-CELL HAVING GRADED DOPING

• US 20120103403A1
• Filed: 10/28/2010
• Published: 05/03/2012
• Est. Priority Date: 10/28/2010
• Status: Active Grant

• Current Assignee: Cactus Materials, Inc.
• Original Assignee: Solar Junction Corporation (The Saudi Technology Development & Investment Co.)
• Inventors: Jones, Rebecca Elizabeth, Fushman, Ilya, Yuen, Homan Bernard, Misra, Pranob, Liu, Ting
• Granted Patent: US 9,214,580 B2
• Time in Patent Office: Days
• US Class Current: 136/255
• CPC Class Codes: H01L 31/03042 characterised by the doping material
• CPC Class Codes: H01L 31/03048 comprising a nitride compounds, e.g. InGaN
• CPC Class Codes: H01L 31/065 the potential barriers being only of the graded gap type
• CPC Class Codes: H01L 31/0687 Multiple junction or tandem solar cells
• CPC Class Codes: H01L 31/0725 Multiple junction or tandem solar cells
• CPC Class Codes: H01L 31/0735 comprising only AIIIBV compound semiconductors, e.g. GaAs/AlGaAs or InP/GaInAs solar cells
• CPC Class Codes: H01L 31/1844 comprising ternary or quaternary compounds, e.g. Ga Al As, In Ga As P
• CPC Class Codes: Y02E 10/544 Solar cells from Group III-V materials

Abstract

A lattice-matched solar cell having a dilute nitride-based sub-cell has exponential doping to thereby control current-carrying capacity of the solar cell. Specifically a solar cell with at least one dilute nitride sub-cell that has a variably doped base or emitter is disclosed. In one embodiment, a lattice matched multi junction solar cell has an upper sub-cell, a middle sub-cell and a lower dilute nitride sub-cell, the lower dilute nitride sub-cell having doping in the base and/or the emitter that is at least partially exponentially doped so as to improve its solar cell performance characteristics. In construction, the dilute nitride sub-cell may have the lowest bandgap and be lattice matched to a substrate, the middle cell typically has a higher bandgap than the dilute nitride sub-cell while it is lattice matched to the dilute nitride sub-cell. The upper sub-cell typically has the highest bandgap and is lattice matched to the adjacent sub-cell. In further embodiments, a multi junction solar cell according to the invention may comprise four, five or more sub-cells in which the one or more sub-cells may each comprise exponentially doped dilute nitride alloys.

Claims

1. A multi junction solar cell comprising:

at least one dilute nitride sub-cell having an emitter, a base and an emitter-base junction, the sub-cell having a doping profile in at least one of the emitter and the base that is dependent upon depth position such that dopant concentration is lowest at the emitter-base junction and increases with distance from the emitter-base junction.

2. The multi junction solar cell according to claim 1, wherein the dopant concentration lies substantially between 1×

10¹⁵/cm³ and 1×

10¹⁹/cm³.

3. The multi junction solar cell of claim 1, the doping being least at the emitter-base junction and increasing exponentially over at least a portion of the distance away from the emitter-base junction.

4. The multi junction solar cell of claim 1, the doping being least at the emitter-base junction and increasing linearly over at least a portion of the distance away from the emitter-base junction.

5. The solar cell of claim 1, wherein the base of the sub-cell has doping with functional dependence on depth position in the base, the doping being least at the emitter-base junction and increasing with distance away from the emitter-base junction, the rate of increase being selected to enhance the efficiency of the solar cell.

6. The solar cell of claim 1, wherein the emitter of the sub-cell has doping with functional dependence on depth position in the emitter, the doping being least at the emitter-base junction and increasing with distance away from the emitter-base junction, the rate of increase being selected to enhance the efficiency of the solar cell.

7. The solar cell of claim 1 having at least three sub-cells, namely a first sub-cell, a second sub-cell and a third sub-cell,

the first sub-cell being the dilute nitride sub-cell, the first sub-cell being lattice matched to an underlying substrate, the dilute nitride sub-cell having a first bandgap among said first, second and third sub-cells that is least;

the second sub cell being on and lattice matched to the first sub-cell and having a second bandgap that is higher than the first bandgap; and

the third sub-cell being formed on the second sub-cell and being lattice matched to the second sub-cell, the third sub-cell being the topmost sub-cell and having a third bandgap higher than the first bandgap and the second bandgap.

8. The multi junction solar cell of claim 1, wherein the base has a first doping subregion and a second doping subregion, the first doping subregion being adjacent the emitter-base junction and having constant doping, and the second doping subregion having doping increasing with distance away from the emitter-base junction.

9. The multi junction solar cell of claim 1, having at least a first sub-cells, a second sub-cell, a third sub-cell and a fourth sub-cell,

the first sub-cell having a first bandgap that is least;

the second sub-cell comprising the dilute nitride sub-cell, the dilute nitride sub-cell being substantially lattice matched to an underlying adjacent structure;

the dilute nitride sub-cell having a bandgap that is greater than the first bandgap;

the third sub-cell being lattice matched to the second sub-cell and having a third bandgap that is greater than the bandgap of second sub-cell; and

the fourth sub-cell being lattice matched to the third sub-cell, the fourth sub-cell having a bandgap greater than the third sub-cell.

10. A multi junction solar cell comprising:

at least one sub-cell having an emitter, a base and an emitter-base junction, wherein the base has a first subregion and a second subregion, the first doping subregion being adjacent the emitter-base junction and having no doping, and the second doping subregion having doping increasing with distance away from the emitter-base junction.

11. The multi junction solar cell of claim 10, wherein the at least one sub-cell is a dilute nitride sub-cell.

12. A method for forming a graded doping profile comprising:

growing a base of a dilute nitride sub-cell of a multi junction solar cell in an atmosphere containing a dopant, the dopant being of a concentration that varies from a maximum to a minimum during the growing to produce a graded doping profile in the base.

13. The method of claim 12 comprising:

annealing the multi junction solar cell containing the dilute nitride sub-cell.

14. A method for forming a graded doping profile comprising:

growing an emitter of a dilute nitride sub-cell of a multi junction solar cell after growing a base, the emitter being grown in an atmosphere containing a dopant, the dopant being of a concentration that varies from a minimum to a maximum during the growing to produce a graded doping profile in the emitter.

15. The method of claim 14 comprising:

annealing the multi junction solar cell containing the dilute nitride sub-cell.