Engineered Substrate with Embedded Mirror for Solar Cells
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Solution Overview
Problem
Conventional substrates for multijunction solar cells suffer from high photon absorption due to doping, leading to reduced efficiency in light detection and conversion, particularly in concentrator photovoltaic applications.
Innovation Solution
An engineered substrate with a seed layer and a support substrate made of non-lattice matched semiconductor materials, where the bonding layers act as both a mirror and a conductive interface, minimizing photon absorption and series resistance, and featuring a metallic bonding interface with high reflection coefficients to enhance photon collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doping is applied to substrates to ensure low contact resistance, then electrical conductivity is improved, but photon absorption increases
Solution Approach 1:
The substrate system is segmented into multiple functional layers: a lightly-doped or undoped semiconductor substrate layer, a metallic bonding layer for electrical contact, and a seed layer for solar cell growth. This segmentation allows the substrate to provide mechanical support and electrical conductivity through the metallic layer without requiring heavy doping of the semiconductor substrate, thereby reducing photon absorption in the substrate region.
Solution Approach 2:
A metallic bonding layer is introduced as an intermediary between the substrate and the solar cell structure. This metallic layer serves as the primary source of electrical conductivity and low contact resistance, eliminating the need to heavily dope the semiconductor substrate. The intermediary metallic layer provides the required electrical properties without the harmful side effect of increased photon absorption that would result from substrate doping.
2Ease of manufacture
If conventional substrates are used, then manufacturing simplicity is maintained, but device efficiency decreases due to high photon absorption
Solution Approach 1:
The substrate system employs a composite structure combining a semiconductor substrate layer with a metallic bonding layer. This composite material approach allows the system to benefit from the mechanical properties of the semiconductor substrate while the metallic layer provides superior electrical conductivity and controlled photon interaction. The composite structure achieves both ease of manufacture (using conventional semiconductor substrates) and high efficiency (through the metallic layer's optical and electrical properties).
Solution Approach 2:
The invention changes the doping parameter of the substrate from heavily doped to lightly-doped or undoped, and introduces a metallic bonding layer with specific thickness and material composition parameters. By optimizing these parameters (substrate doping concentration, metallic layer thickness and material), the system achieves low photon absorption while maintaining electrical conductivity and manufacturability.
3Reliability
If substrate doping is increased to reduce series resistance, then electrical conductivity is improved, but photon absorption increases
Solution Approach 1:
The electrical conduction function is segmented from the substrate to the metallic bonding layer. The substrate is kept lightly-doped or undoped to minimize photon absorption, while the metallic bonding layer carries the electrical current and provides low series resistance. This functional segmentation resolves the contradiction by placing the electrical conduction responsibility in the metallic layer rather than relying on substrate doping.
Solution Approach 2:
The metallic bonding layer acts as an intermediary that provides the electrical conduction pathway, replacing the need for high substrate doping. This intermediary layer delivers the required low series resistance performance without introducing the harmful photon absorption that would result from doping the semiconductor substrate.
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 engineered substrate achieves less than 20% photon absorption and a series resistance of less than 10 mOhm·cm², significantly improving the efficiency of solar cells by recycling unabsorbed photons and maintaining low electrical resistivity.
Implementation Method 1
The bonding interface between the first and second bonding layers thereby has the function of a mirror layer of metallic material in order to better reflect photons. The incoming photons that have not been absorbed by the active device grown on top of the seed layer during their first path can then be reflected at the mirror layer and be reinjected in the active device for absorption.
Data Source
AI summary
An engineered substrate comprising: a seed layer made of a first semiconductor material for growth of a solar cell; a first bonding layer on the seed layer; a support substrate made of a second semiconductor material; a second bonding layer on a first side of the support substrate; a bonding interface between the first and second bonding layers; the first and second bonding layers each made of metallic material; wherein doping concentration and thickness of the engineered substrate, in particular, of the seed layer, the support substrate, and both the first and second bonding layers, are selected such that the absorption of the seed layer is less than 20%, preferably less than 10%, as well as total area-normalized series resistance of the engineered substrate is less than 10 mOhm·cm2, preferably less than 5 mOhm·cm2.