Germanium Solar Cell Junctions via Low-Temperature Alloying
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Solution Overview
Problem
Conventional high-temperature processes for forming electrical junctions in crystalline Ge solar cells are not compatible with low-cost handle substrates, leading to high fabrication costs and reduced efficiency due to low open-circuit voltage and insufficient surface passivation.
Innovation Solution
The use of low-temperature processes to form doped germanium-containing substrates with wider-bandgap contacts, including n-type and p-type materials with specific electron and hole affinities, and the incorporation of passivation layers to improve open-circuit voltage without compromising fill-factor, suitable for integration with low-cost flexible substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature processes are used to form electrical junctions in crystalline Ge solar cells, then the electrical junctions can be formed, but the process is not compatible with low-cost handle substrates and increases fabrication cost
Solution Approach 1:
The patent applies parameter changes by transitioning from high-temperature processes (above 425°C) to low-temperature processes (below 200°C) for forming electrical junctions. This is achieved by changing the material composition to include wider-bandgap materials such as silicon-germanium alloys and amorphous silicon, which enable junction formation at lower temperatures compatible with plastic and flexible substrates.
Solution Approach 2:
The patent employs composite materials by combining germanium with silicon to form silicon-germanium alloys, and by integrating amorphous silicon layers with crystalline germanium substrates. These composite structures enable low-temperature processing while maintaining the necessary electrical properties for solar cell operation.
2Reliability
If conventional crystalline Ge solar cell structures are used, then the device can operate, but the open-circuit voltage is low due to low bandgap and insufficient surface passivation
Solution Approach 1:
The patent uses composite materials including wider-bandgap materials such as silicon-germanium alloys and amorphous silicon layered structures. These materials have higher bandgaps than pure germanium, which directly increases the open-circuit voltage while still allowing the device to operate effectively.
Solution Approach 2:
The patent introduces amorphous silicon layers as intermediary elements between the crystalline germanium substrate and the metal contacts. These intermediary layers provide superior surface passivation, reducing recombination losses and increasing open-circuit voltage.
3Reliability
If high-temperature processes are used, then electrical junctions can be formed, but the bulk-lifetime of the absorption layer is compromised and Ge wafers may be degraded
Solution Approach 1:
The patent changes the temperature parameter from high (above 425°C) to low (below 200°C) for the junction formation process. This parameter change preserves the bulk-lifetime of the absorption layer and prevents degradation of Ge wafers while still achieving functional electrical junctions through the use of wider-bandgap materials.
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 enhances the open-circuit voltage of photovoltaic devices while reducing process temperatures, preserving the bulk-lifetime of the absorption layer and enabling the use of low-cost, flexible substrates, thereby lowering fabrication costs and improving solar cell efficiency.
Implementation Method 1
A photovoltaic device includes a doped germanium-containing substrate
Implementation Method 2
the at least one doped layer of the emitter contact or the back contact includes an n-type material having an electron affinity smaller than that of the substrate, or a p-type material having a hole affinity larger than that of the substrate
Implementation Method 3
The passivation layer 16 improves the solar cell efficiency by reducing the recombination of electron-hole pairs at the surface of the emitter layer
Data Source
AI summary
A photovoltaic device and method include a doped germanium-containing substrate, an emitter contact coupled to the substrate on a first side and a back contact coupled to the substrate on a side opposite the first side. The emitter includes at least one doped layer of an opposite conductivity type as that of the substrate and the back contact includes at least one doped layer of the same conductivity type as that of the substrate. The at least one doped layer of the emitter contact or the at least one doped layer of the back contact is in direct contact with the substrate, and the at least one doped layer of the emitter contact or the back contact includes an n-type material having an electron affinity smaller than that of the substrate, or a p-type material having a hole affinity larger than that of the substrate.