Group-IV Heterostructure Solar Cells With Tuned Tunnel Junctions

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Solution Overview

Problem

Existing multijunction solar cells face limitations in efficiency due to high series resistance, current mismatch, and parasitic losses, particularly in subcells with low current densities and large base thicknesses, which impair overall performance.

Innovation Solution

Incorporation of group-IV subcells with heterostructures, utilizing materials like Ge, SiGe, and SiGeSn, and III-V subcells, with optimized doping and lattice-matched growth processes to form tunnel junctions and p-n junctions, reducing minority-carrier recombination and enhancing transparency, while managing dopant diffusion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If lattice-matched subcells are used in multijunction solar cells, then manufacturing reliability is improved, but efficiency is limited due to high series resistance and current mismatch

Engineering Contradiction:

Improvemanufacturing reliabilityVSAvoidpower generation efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent changes the material parameters by transitioning from traditional lattice-matched III-V subcells to group-IV subcells (Ge, SiGe, SiGeSn) with different lattice constants and bandgaps. This parameter change enables lower series resistance and improved current matching while maintaining manufacturing reliability through controlled epitaxial growth processes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material structures by combining different group-IV materials (Ge, SiGe, SiGeSn) with varying compositions and properties in a single multijunction cell. This composite approach allows optimization of each subcell's electrical and optical characteristics to reduce series resistance and improve overall efficiency.

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If subcells with large base thicknesses are used, then light absorption is improved, but parasitic losses increase and efficiency decreases

Engineering Contradiction:

Improvelight absorptionVSAvoidparasitic losses

Core Design Contradiction:

Use of energy by moving objectVSLoss of energy

Solution Approach 1:

The patent applies local quality by optimizing the base thickness of each group-IV subcell individually according to its specific bandgap and absorption characteristics. Rather than using uniform thick bases throughout, each subcell's base thickness is locally tailored to maximize light absorption while minimizing parasitic losses in that specific region.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the base thickness parameter for each subcell to optimize the balance between light absorption and parasitic losses. By adjusting this critical dimension parameter for Ge, SiGe, and SiGeSn subcells differently, the design achieves improved efficiency without sacrificing absorption capability.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If conventional tunnel junctions are used for interconnection, then series connection is achieved, but current mismatch and voltage output are limited

Engineering Contradiction:

Improveelectrical interconnectionVSAvoidvoltage output

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent changes the electrical parameters of the tunnel junctions by using group-IV materials with optimized doping concentrations and junction depths. This parameter optimization reduces current mismatch between subcells and enables higher voltage output while maintaining reliable series interconnection.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses identical group-IV materials for both the subcell bases and the tunnel junctions, creating a material copying strategy. This approach ensures compatible electrical properties and reduces interface resistance, improving both interconnection reliability and voltage output.

Inventive Principle:

Principle #26Copying

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

This approach significantly improves the efficiency and voltage output of multijunction solar cells, enabling higher current matching and reduced parasitic losses, leading to enhanced power generation capabilities.

Implementation Method 1

photovoltaic cells offer a valuable means for providing power generation by converting the abundant resource of the sun's energy to electrical power

Methodology Applied

Scientific EffectPhotovoltaic effect: Photovoltaic Effect

Implementation Method 2

managing dopant diffusion

Methodology Applied

Scientific EffectDopant diffusion: Diffusion

Data Source

PatentUS12610625B2Group-IV solar cell structure using group-IV heterostructures

Publication Date: 2026.04.21 THE BOEING CO

AI summary

Photovoltaic cells including a first group-IV subcell including an n-type emitter layer comprising a first group-IV material selected from a first group consisting of Ge, SiGe and SiGeSn, and a second layer comprising a second group-IV material, the second group-IV material being different from the first group-IV material, and the n-type emitter layer being the primary photoabsorber of the first group-IV subcell. A p-n junction of the first group-IV subcell is formed at a heterojunction of the n-type emitter layer and second layer. The photovoltaic cell also includes a tunnel junction, and a second group-IV subcell, the tunnel junction interconnecting the first group IV subcell to the second group-IV subcell, the first group IV subcell and the second group IV subcell being a lowest two subcells of the photovoltaic cell, the first group IV subcell being between the second group-IV subcell and a plurality of HI-V subcells.