Polysilicon Layer Segmentation for Photovoltaic Cell Parasitic Absorption
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Solution Overview
Problem
State-of-the-art bifacial photovoltaic cells with thick doped polysilicon layers suffer from parasitic absorption of photons, leading to decreased short-circuit current due to the thickness required to dispense with expensive transparent conductive oxide layers, and etching processes are not reproducible or homogeneous.
Innovation Solution
A method involving a crystalline silicon substrate with a tunnel oxide film, a polysilicon layer, and a first antireflection layer to create free areas between electrical contacts, followed by thermal oxidation to form a second antireflection layer, reducing polysilicon thickness and parasitic absorption while maintaining passivation and reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a thick doped polysilicon layer is used to dispense with expensive transparent conductive oxide layers, then manufacturing cost is reduced, but parasitic absorption of photons increases leading to decreased short-circuit current
Solution Approach 1:
The polysilicon layer is segmented into two distinct parts with different thicknesses: a first part under the electrical contacts with greater thickness for conductivity, and a second part between the contacts with reduced thickness to minimize parasitic absorption. This segmentation allows each region to be optimized for its specific function.
Solution Approach 2:
Different regions of the polysilicon layer are given different local properties: the region under contacts has high thickness for electrical conductivity, while the region between contacts has reduced thickness to minimize optical absorption. This local differentiation resolves the contradiction between conductivity requirements and optical performance.
2Ease of manufacture
If a thick doped polysilicon layer is used, then the need for transparent conductive oxide layers is eliminated, but open circuit voltage increases are limited due to parasitic absorption
Solution Approach 1:
The polysilicon layer is divided into functional segments: a thick first part for electrical contact and a thin second part for minimal optical interference. This segmentation enables the structure to achieve both manufacturing simplicity and high open circuit voltage by eliminating parasitic absorption in the light-path region.
Solution Approach 2:
The local thickness of the polysilicon layer is optimized for different functions: thick where electrical conductivity is needed, thin where optical transparency is critical. This local quality differentiation allows the structure to achieve high open circuit voltage while maintaining manufacturing simplicity.
3Object-generated harmful factors
If etching processes are used to reduce polysilicon layer thickness, then parasitic absorption is reduced, but process reproducibility and homogeneity deteriorate
Solution Approach 1:
The mechanical/chemical etching process is replaced with a deposition-based approach. Instead of removing material through etching, the solution deposits a first antireflection layer that selectively protects certain regions, then uses thermal oxidation to uniformly reduce thickness. This substitution eliminates the reproducibility issues associated with etching while achieving the same parasitic absorption reduction.
Solution Approach 2:
A first antireflection layer is introduced as an intermediary protective layer during the thermal oxidation process. This intermediary layer selectively protects the polysilicon under contacts while allowing oxidation in the regions between contacts, enabling precise thickness control without direct etching and thereby ensuring process reproducibility.
4Object-generated harmful factors
If the polysilicon layer thickness is reduced to minimize parasitic absorption, then short-circuit current increases, but passivation quality may deteriorate
Solution Approach 1:
The polysilicon layer is segmented into a first part that maintains sufficient thickness for passivation under the contacts, and a second part with reduced thickness for minimal parasitic absorption between contacts. This segmentation allows the structure to simultaneously achieve high short-circuit current and maintain passivation quality where needed.
Solution Approach 2:
The polysilicon layer exhibits local quality differentiation: sufficient thickness under contacts for effective passivation, and reduced thickness between contacts to minimize parasitic absorption. This local optimization allows the structure to achieve both high short-circuit current and maintained passivation quality in critical regions.
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 reduces parasitic absorption, enhances passivation, and increases open circuit voltage while maintaining industrial feasibility and avoiding damage to the structure.
Implementation Method 1
the first antireflection layer being adapted to provide a barrier to thermal oxidation of said part of the polysilicon layer
Implementation Method 2
thermally oxidizing the free areas of the polysilicon layer so as to form a second antireflection layer on said free areas
Data Source
Figure 1~4
AI summary
This process comprises the steps: a) providing a crystalline silicon substrate (1), comprising: - a first surface (10); - a second surface (11), opposite the first surface (10), and covered with at least one tunnel oxide film (2); b) forming a polysilicon layer on the tunnel oxide film (2); c) forming a first antireflection layer (4) on a portion (3a) of the polysilicon layer so that the polysilicon layer has free zones, the first antireflection layer (4) being suitable for providing a barrier to the thermal oxidation of said portion (3a) of the polysilicon layer (3); d) thermally oxidizing the free zones of the polysilicon layer so as to form a second antireflection layer (5) on said free zones.