Compositionally-Graded Amorphous Semiconductor Layer for Solar Cells
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Solution Overview
Problem
Existing photovoltaic devices face challenges in minimizing charge-carrier recombination at interface regions due to structural imperfections and impurity accumulation, leading to decreased photoelectric conversion efficiency, and current fabrication methods introduce additional defects and contamination risks.
Innovation Solution
A compositionally-graded amorphous semiconductor layer is formed over a semiconductor substrate, gradually changing from intrinsic to conductive through its depth, eliminating the need for discrete intrinsic and conductive layers and reducing interface states, thereby minimizing recombination and contamination risks during fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete intrinsic and conductive layers are used to passivate the substrate surface, then charge carrier recombination is reduced, but additional interface regions are created that can trap impurities and cause further recombination
Solution Approach 1:
The patent combines the intrinsic and conductive layers into a single compositionally-graded layer that transitions continuously from intrinsic at the substrate interface to conductive at the outer surface. This merging eliminates the additional interface between discrete intrinsic and conductive layers, reducing impurity trapping sites while maintaining the passivation function and charge carrier collection efficiency.
Solution Approach 2:
The compositionally-graded layer exhibits local quality variation through its depth, being substantially intrinsic at the interface with the substrate and substantially conductive at the opposite side. This spatial variation in electrical properties allows the single layer to perform both passivation (intrinsic region) and charge carrier collection (conductive region) functions without creating additional harmful interfaces.
2Reliability
If multiple deposition steps are used to create discrete layers, then specific electrical properties are achieved, but opportunities for contamination and defect introduction increase
Solution Approach 1:
The compositionally-graded layer is formed by continuous deposition of semiconductor material and dopant without interruption between intrinsic and conductive layer formation. This continuous deposition process eliminates the deposition step interruptions that would otherwise allow impurities and contaminants to enter the structure, while still achieving the desired electrical property gradient through controlled dopant concentration variation.
Solution Approach 2:
The patent achieves different electrical properties within a single continuous layer by changing the dopant concentration parameter during deposition. The dopant concentration is varied continuously from zero (intrinsic) at the substrate interface to a higher value (conductive) at the outer surface, allowing the layer to perform multiple electrical functions without requiring multiple discrete deposition steps.
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 enhances photoelectric conversion efficiency by reducing recombination and interface defects, while simplifying the fabrication process and minimizing contamination, resulting in improved electrical properties and efficient energy conversion.
Implementation Method 1
Photovoltaic devices convert radiation, such as solar, incandescent, or fluorescent radiation, into electrical energy. The conversion to electrical energy is achieved by the well-known photovoltaic effect.
Implementation Method 2
The presence of this intrinsic layer decreases the recombination of charge carriers at the substrate surface, and thereby improves the performance of the photovoltaic device.
Data Source
AI summary
A semiconductor structure is described, including a semiconductor substrate of one conductivity type; and an amorphous semiconductor layer disposed on at least one of its surfaces. The amorphous semiconductor layer is compositionally graded through its depth, from substantially intrinsic at the interface with the substrate, to substantially conductive at the opposite side. Photovoltaic devices which include such a structure are also disclosed, as are solar modules made from one or more of the devices. Related methods are also described.