Delta-Doped Tunnel Junctions for Multijunction Solar Cells
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The electrical characteristics of interconnecting tunnel junctions in multijunction solar cells are limited by low dopant concentrations and thickness constraints, which restrict the peak current handling capacity and efficiency, especially under high concentration illumination.
Innovation Solution
A delta-doped layer with a dopant concentration approximately 10 times greater than the underlying layer is introduced within the interconnecting tunnel junction, achieving a peak dopant concentration of 10^20 cm^-3 and a width of 20 Angstroms, enhancing the current handling capability by positioning the delta-doped layer close to the junction interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a highly doped layer is introduced to increase peak tunneling current density, then the current handling capability is improved, but the layer thickness must be kept extremely thin which complicates the manufacturing process
Solution Approach 1:
The patent applies delta-doping to achieve extremely high dopant concentrations (10^20 to 10^21 atoms/cm³) in a thin layer (20-50 Å), fundamentally changing the doping parameter from conventional levels to ultra-high levels. This enables the tunnel junction to achieve peak current densities of 30 A/cm² or higher while maintaining the required thin layer structure for optimal tunneling performance
Solution Approach 2:
The patent transitions from conventional bulk doping to delta-doping, which introduces dopants in a two-dimensional plane rather than throughout a three-dimensional volume. This dimensional change allows the dopants to be concentrated in an extremely thin layer (20-50 Å) at a specific position within the tunnel junction, achieving ultra-high dopant concentration without significantly increasing the overall layer thickness
2Power
If the dopant concentration is increased to improve electrical characteristics, then the current carrying capacity is enhanced, but the optical transparency may be compromised
Solution Approach 1:
The patent applies delta-doping to create a highly doped region (20-50 Å thick) only at the specific location where the tunnel junction interface is formed, while the rest of the tunnel junction layers maintain their intrinsic or lightly doped state. This localized doping approach enhances the electrical characteristics at the critical interface region without introducing excessive dopants throughout the entire structure that would degrade optical transparency
Solution Approach 2:
The patent uses delta-doping to introduce an extremely high concentration of dopants (10^20 to 10^21 atoms/cm³) in a very thin layer, which is an excessive doping level compared to conventional doping. However, because this excessive doping is confined to such a thin layer (20-50 Å) at the junction interface, the overall optical transparency of the thicker tunnel junction structure is preserved
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The delta-doped layer significantly increases the peak tunneling current density by approximately a factor of two, improving the current carrying capacity and efficiency of the multijunction solar cell without compromising optical transparency.
Implementation Method 1
a narrow, delta-doped layer within the interconnecting tunnel junction that improves the current handling capability
Implementation Method 2
a second layer of said tunnel diode of a second complementary p/n type semiconductor material to said first layer of said tunnel diode and said delta-dope layer, said second layer grown epitaxially on said delta-doped layer
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A highly doped layer for interconnecting tunnel junctions in multijunction solar cells is presented. The highly doped layer is a delta doped layer in one or both layers of a tunnel diode junction used to connect two or more p-on-n or n-on-p solar cells in a multijunction solar cell. A delta doped layer is made by interrupting the epitaxial growth of one of the layers of the tunnel diode, depositing a delta dopant at a concentration substantially greater than the concentration used in growing the layer of the tunnel diode, and then continuing to epitaxially grow the remaining tunnel diode.