Graded Silicon Solar Cell Layers for Lower Recombination Loss
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Solution Overview
Problem
Solar cells face reduced efficiency due to charge carrier recombination at surface defects and interface states, which are exacerbated by the presence of intrinsic layers that also increase resistivity and band bending.
Innovation Solution
A layered structure comprising a first layer with a higher percentage of crystalline material within an amorphous matrix, interposed between a second layer with a lower percentage of crystalline material and the substrate, reduces resistivity and enhances light absorption, thereby improving charge carrier transport and photovoltaic conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intrinsic layer is formed between the substrate and doped layers to passivate surface defects, then charge carrier recombination at the substrate surface is reduced, but the intrinsic layer creates additional interfaces that accumulate impurities and increase charge carrier recombination
Solution Approach 1:
The patent changes the structural parameter of the intrinsic layer by introducing a graded crystalline material composition. The crystalline content increases from the substrate interface toward the doped layer interface, creating a gradient structure that reduces abrupt interface transitions. This parameter change minimizes interface state density while maintaining passivation effectiveness, resolving the contradiction between surface passivation and interface recombination.
Solution Approach 2:
The patent employs a composite structure within the intrinsic layer by combining amorphous and crystalline silicon materials in a graded ratio. The layer transitions from predominantly amorphous near the substrate to increasingly crystalline toward the doped layer interface. This composite approach allows the layer to simultaneously provide passivation (amorphous component) and reduce interface states (crystalline component), resolving the harmful effects of traditional homogeneous intrinsic layers.
2Reliability
If the intrinsic layer is made thicker to improve passivation, then surface defect effects are reduced, but the resistivity of the solar cell increases due to inhibited charge carrier transportation
Solution Approach 1:
The patent changes the compositional parameter of the intrinsic layer by implementing a crystalline gradient. The increasing crystalline content from substrate toward the doped layer progressively improves charge carrier mobility throughout the layer thickness. This allows the layer to maintain adequate passivation (sufficient thickness) while the crystalline regions facilitate charge carrier transport, reducing resistive losses compared to a homogeneous amorphous layer of the same thickness.
Solution Approach 2:
The patent applies local quality variation within the intrinsic layer by creating different material compositions at different positions. The region near the substrate remains more amorphous for effective passivation, while the region near the doped layer interface becomes more crystalline to facilitate charge carrier extraction. This spatial variation in material quality allows simultaneous optimization of both passivation and charge carrier transport functions.
3Ease of manufacture
If a traditional homogeneous intrinsic layer is used, then the structure is simple to manufacture, but the abrupt interface creates band bending and high density of interface states leading to charge carrier recombination
Solution Approach 1:
The patent implements a continuous parameter change in the intrinsic layer by gradually varying the crystalline material ratio from the substrate interface to the doped layer interface. This graded transition eliminates abrupt discontinuities in material properties, reducing band bending and interface state formation. The continuous gradient can be achieved through controlled deposition processes, maintaining manufacturing feasibility while dramatically improving interface quality.
Solution Approach 2:
The patent introduces dynamic composition variation within the intrinsic layer rather than a static homogeneous structure. The crystalline content dynamically increases through the layer thickness, creating a progressive transition zone. This dynamic compositional change allows the interface to adapt gradually between the amorphous substrate region and the doped layer region, minimizing abrupt transitions and associated interface defects.
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 layered structure increases the fill factor and short circuit current of solar cells by reducing contact resistivity and enhancing light absorption, while maintaining effective passivation of the substrate surface with a thinner passivation layer.
Implementation Method 1
The inclusion of a higher concentration of crystalline material in the first layer reduces the resistivity of the layered structure away from the substrate. As such, the contact resistivity between the layered structure and an electrode of the solar cell may be reduced which thereby increases the fill factor of the solar cell.
Implementation Method 2
Conversely, the higher concentration of amorphous material in the second layer leads to increased light absorption towards the surface of the substrate, thereby increasing the short circuit current (lsc) and hence the performance of the solar cell.
Implementation Method 3
The recombination of the charge carriers is one of the main reasons for decreased photovoltaic conversion efficiency of a solar cell. The inclusion of a higher concentration of crystalline material in the first layer reduces the resistivity of the layered structure away from the substrate, thereby increasing the fill factor of the solar cell.
Data Source
AI summary
A solar cell comprising a silicon substrate and a layered structure arranged on a surface of the silicon substrate, the layered structure comprising; a first layer comprising a percentage of crystalline material arranged within an amorphous matrix, the first layer being arranged on the surface of the silicon substrate; a second layer comprising a percentage of crystalline material arranged within an amorphous matrix, the second layer being interposed between the first layer and the surface of the silicon substrate; wherein the percentage of crystalline material in the first layer is greater than the percentage of crystalline material in the second layer.