Nanostructured Solar Cell Antireflection Coating
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Solution Overview
Problem
Conventional solar cells have efficiency limitations due to non-planar junctions, which increase solar cell saturation current and reduce light capture efficiency, particularly in silicon-based photovoltaic cells.
Innovation Solution
The formation of a nanostructured surface on silicon solar wafers using a wavelike silicon nitride nanomask created by nitrogen ion beam irradiation and subsequent etching, resulting in a quasi-periodic array of elongated ridge elements with a wave-ordered structure, which reduces reflection and allows for a planar p-n junction, potentially increasing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a pyramidal textured surface is used to improve light capture, then light absorption is improved, but the junction surface area increases by 1.7 times which increases saturation current and reduces efficiency
Solution Approach 1:
The patent segments the antireflection coating into multiple layers with different refractive indices (e.g., silicon nitride layer with n=2.0 and silicon oxide layer with n=1.46). This multi-layer segmentation allows progressive impedance matching between air and silicon, reducing reflection without requiring a highly textured surface, thus maintaining a planar junction and low saturation current while achieving excellent light absorption.
Solution Approach 2:
The patent changes the optical parameters by using multiple layers with specifically controlled thicknesses and refractive indices. The first layer has thickness d1 and refractive index n1, the second layer has thickness d2 and refractive index n2, where these parameters are optimized to achieve minimum reflection across the solar spectrum. This parameter optimization reduces the need for surface texturing, allowing a planar junction to be maintained.
2Loss of energy
If a planar junction is used to reduce saturation current, then efficiency is improved, but light capture is reduced compared to textured surfaces
Solution Approach 1:
The patent uses a composite antireflection structure consisting of multiple layers with different optical properties (silicon nitride, silicon oxide, and potentially other materials). This composite structure creates a gradient refractive index profile that progressively matches the impedance between air and silicon, enabling a planar junction to achieve the same light absorption as textured surfaces without the penalty of increased junction area and saturation current.
Solution Approach 2:
Instead of solving the light capture problem in the spatial dimension through surface texturing, the patent transitions to solving it in the optical dimension through multi-layer interference effects. By controlling the thickness and refractive index of each layer, the structure achieves constructive interference for light absorption while maintaining a planar geometric profile, thus avoiding increased junction area.
3Ease of manufacture
If conventional single-layer antireflection coating is used, then manufacturing is simple, but reflection is not sufficiently reduced across the solar spectrum
Solution Approach 1:
The patent divides the antireflection function into multiple sequential layers, each with a specific refractive index and thickness. The first layer (e.g., silicon nitride) provides initial impedance matching, while the second layer (e.g., silicon oxide) provides further matching. This segmentation allows each layer to be optimized for its specific function, achieving broad-spectrum antireflection performance that a single layer cannot achieve alone.
Solution Approach 2:
The patent optimizes multiple parameters including the refractive index, thickness, and material composition of each layer. By independently controlling parameters d1, n1, d2, n2 for each layer, the structure achieves minimum reflection across the entire solar spectrum. This multi-parameter optimization provides superior optical performance compared to single-layer coatings while remaining manufacturable through standard deposition techniques.
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 solar cell efficiency by reducing saturation current and light reflection, potentially increasing conversion efficiency by up to 10% or more, and eliminates the need for antireflection coatings.
Implementation Method 1
a wavelike silicon nitride nanomask created by nitrogen ion beam irradiation
Implementation Method 2
to reduce the reflection of light from their surface
Data Source
AI summary
A solar cell includes a base and a nanostructured layer formed on the base. The nanostructured layer has a nanostructured surface opposite the base. The nanostructured surface has a quasi-periodic, anisotropic array of elongated ridge elements having a wave-ordered structure pattern, each ridge element having a wavelike cross-section and oriented substantially in a first direction.