Multilayer Window Structure for Solar Cell
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Solution Overview
Problem
Conventional multijunction solar cells face efficiency losses due to high light absorption in the window layer, which leads to increased minority carrier surface recombination velocity and reduced photocarrier collection, especially in the top subcell where the window layer absorbs a significant fraction of incident photons.
Innovation Solution
A multilayer window structure is introduced, where the bottom layer has intrinsic material lattice spacing matching the emitter, minimizing light absorption and surface recombination, while upper layers have progressively higher band gaps achieved through varying intrinsic material lattice spacings, reducing overall light absorption and enhancing current collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer window layer with lattice-matched emitter is used, then a high-quality emitter-window interface is achieved, but light absorption in the window layer increases leading to reduced photocarrier collection
Solution Approach 1:
The window layer is segmented into multiple sublayers with progressively varying band gaps and lattice constants. The bottom sublayer maintains lattice matching with the emitter for interface quality, while upper sublayers have increasing band gaps to reduce light absorption. This segmentation allows simultaneous optimization of both interface quality and light transmission.
Solution Approach 2:
Different sublayers of the window structure are assigned different local properties: the bottom sublayer has lattice-matched properties for optimal interface quality, while upper sublayers have progressively higher band gaps for reduced light absorption. Each sublayer is optimized for its specific function within the overall structure.
2Productivity
If the window layer band gap is increased to reduce light absorption, then light transmission improves, but the lattice mismatch with the emitter increases causing interface degradation
Solution Approach 1:
The window layer is divided into multiple sublayers with gradual band gap progression. The bottom sublayer maintains lattice matching with the emitter, while upper sublayers progressively increase band gap. This gradual transition prevents sudden lattice mismatch and maintains interface quality while achieving reduced light absorption.
Solution Approach 2:
The band gap and lattice constant parameters are systematically varied across the window layer thickness. By changing these parameters progressively from the bottom to top sublayers, the structure achieves both reduced light absorption (higher band gap) and maintained interface quality (lattice matching at the emitter interface).
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 multilayer window structure improves current collection and overall solar cell efficiency by minimizing light absorption in the window layer and maintaining a high-quality emitter-window interface, resulting in increased photocarrier collection and efficiency gains up to 0.4 mA/cm2 under the AM1.5D spectrum.
Implementation Method 1
A window layer is part of the active semiconductor structure but may also constitute part or all of an antireflection coating. The window layer on top of an emitter to passivate the emitter surface and reflect back minority carriers to inhibit surface recombination
Implementation Method 2
A window layer is part of the active semiconductor structure but may also constitute part or all of an antireflection coating. The window layer on top of an emitter to passivate the emitter surface and reflect back minority carriers to inhibit surface recombination that reduces efficiency
Implementation Method 3
One or more upper layers of the window structure has progressively higher band gaps than the bottom layer and has intrinsic material lattice spacing that is substantially different than the emitter intrinsic material lattice spacing. Compared to a conventional window layer that is uniform in composition and has the same intrinsic material lattice spacing as the emitter, the multi-layer window structure decreases the light absorption in the window structure and improves the overall current collection of the subcell
Data Source
AI summary
A multilayer window structure for a solar cell comprises one or more layers where the bottom layer has an intrinsic material lattice spacing that is substantially the same as the emitter in the plane perpendicular to the direction of epitaxial growth. One or more upper layers of the window structure has progressively higher band gaps than the bottom layer and has intrinsic material lattice spacing is substantially different than the emitter intrinsic material lattice spacing.