Double Emitter Structure for Photovoltaic Cells
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Solution Overview
Problem
Existing emitter structures for photovoltaic cells face challenges such as poor short-wavelength response, increased recombination, and junction leakage due to heavy doping, and require additional processing steps like lithography, which are not industrially applicable for large-scale production.
Innovation Solution
A method for forming a double emitter structure with a thick, moderately doped first emitter region and a thin, highly doped second emitter region, where the second emitter region is grown on a textured surface, providing a textured interface that enhances short-wavelength response and reduces junction leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a highly doped emitter region is formed at the front surface to achieve good contact resistance, then contact resistance is improved, but short-wavelength response deteriorates due to heavy doping effects and increased recombination
Solution Approach 1:
The emitter structure is segmented into two distinct regions: a first emitter region with moderate doping concentration and a second emitter region with high doping concentration. The moderate doping first emitter region (10^15 to 10^19 cm^-3) provides good short-wavelength response by reducing heavy doping effects, while the highly doped second emitter region (10^19 to 10^21 cm^-3) ensures low contact resistance for the metal grid. This segmentation allows both regions to perform their respective functions optimally without compromising each other.
Solution Approach 2:
Different doping concentrations are applied to different spatial locations within the emitter structure. The first emitter region has moderate doping concentration optimized for optical response, while the second emitter region has high doping concentration optimized for electrical contact. This local differentiation of doping quality enables the structure to simultaneously achieve good short-wavelength response and low contact resistance.
2Ease of manufacture
If a selective emitter structure with highly doped region underneath metal grid and lightly doped region between contacts is used to improve short-wavelength response, then short-wavelength response is improved, but device complexity increases due to additional processing steps like lithography
Solution Approach 1:
The patent employs periodic alternation between epitaxial growth phases and doping phases to form the dual emitter structure. During epitaxial growth, semiconductor layers are deposited periodically, and during doping phases, dopants are introduced at specific intervals. This periodic process sequence enables the formation of the moderate doping first emitter region followed by the highly doped second emitter region without requiring complex lithographic patterning, thus reducing device complexity while achieving the desired selective doping profile.
3Ease of manufacture
If a CVD-grown emitter is formed on a non-textured surface to simplify processing, then processing is simplified, but reflection losses at the front surface increase
Solution Approach 1:
The patent applies surface texturing to the first emitter region before forming the second emitter region. This preliminary texturing action creates a textured interface that reduces reflection losses and enhances light trapping. By performing the texturing operation before the final emitter formation, the structure benefits from reduced reflection while maintaining processing simplicity, as the subsequent epitaxial growth of the second emitter region occurs on the pre-textured surface.
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 solution results in improved short-wavelength response, good contact resistance, and reduced sensitivity to metal penetration leakage, while avoiding the need for precise alignment of the metal grid, thus enhancing the performance and efficiency of photovoltaic cells.
Implementation Method 1
texturing a surface of the first layer may comprise plasma etching the first layer
Implementation Method 2
forming the second emitter region may comprise growing the second emitter region on the first textured surface. Growing the second emitter region may comprise epitaxially growing the second emitter region
Implementation Method 3
The emitter diffusion process is usually performed at the front surface of the photovoltaic cell
Data Source
AI summary
A method for forming an emitter structure on a substrate and emitter structures resulting therefrom is disclosed. In one aspect, a method includes forming, on the substrate, a first layer comprising semiconductor material. The method also includes texturing a surface of the first layer, thereby forming a first emitter region from the first layer, wherein the first emitter region has a first textured surface. The method also includes forming a second emitter region at the first textured surface, the second emitter region having a second textured surface.