Selenium-Graded Photovoltaic Absorber Without CdS Window Layer
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Solution Overview
Problem
Thin film solar cells, such as those with cadmium telluride/cadmium sulfide (CdTe/CdS) heterojunctions, face limitations in conversion efficiency due to light absorption by the window layer and lattice mismatch at the interface, leading to defects and reduced performance, necessitating improved configurations and manufacturing methods.
Innovation Solution
A photovoltaic device configuration that eliminates the cadmium sulfide layer by using a selenium absorber layer with varying atomic concentration across its thickness, forming a p-n junction within the absorber layer to enhance efficiency and reduce optical losses, while maintaining or improving open circuit voltage and fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a window layer is used to form heterojunction with absorber layer, then electrical performance is improved, but optical losses increase due to light absorption by the window layer
Solution Approach 1:
The patent removes the separate window layer (CdS) from the device structure and instead creates window layer functionality through a selenium gradient within the absorber layer itself. The selenium concentration varies from high at the front interface to low at the back, effectively creating an in-situ window region that eliminates the need for a distinct window layer and reduces optical losses.
Solution Approach 2:
The patent combines the window layer function and absorber layer function into a single integrated absorber layer with compositional grading. The selenium gradient creates a functional gradient within the layer, where the high-selenium region performs window layer duties while the low-selenium region performs absorption, merging two separate layers into one.
2Loss of energy
If window layer thickness is reduced to reduce optical losses, then conversion efficiency improves, but open circuit voltage and fill factor decrease
Solution Approach 1:
The patent applies local quality by creating a selenium concentration gradient within the absorber layer. The high-selenium region at the front interface provides the necessary electrical properties for high open circuit voltage and fill factor, while the low-selenium region at the back maintains light absorption capability. This spatial variation in composition allows simultaneous optimization of electrical and optical properties.
Solution Approach 2:
The patent changes the compositional parameter (selenium concentration) across the thickness of the absorber layer to achieve different functional regions. By varying the selenium concentration from high to low across the layer thickness, the patent optimizes both electrical performance (through high selenium at interface) and optical performance (through low selenium at absorption region) within a single layer.
3Reliability
If CdS/CdTe heterojunction is used, then p-n junction is formed, but lattice mismatch leads to high defect density at interface
Solution Approach 1:
The patent changes the compositional parameter continuously across the interface by incorporating a selenium gradient. This gradual compositional transition reduces the abrupt lattice mismatch that occurs in conventional CdS/CdTe heterojunctions, thereby reducing defect density at the interface while maintaining p-n junction functionality.
Solution Approach 2:
The patent creates a composite absorber layer with varying selenium content, effectively creating a composite material structure within a single layer. This composite approach allows optimization of lattice matching and defect reduction while maintaining the necessary heterojunction properties for charge separation.
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 selenium-based configuration improves conversion efficiency, reduces optical losses, and potentially lowers production costs by eliminating or reducing the need for cadmium sulfide, while enhancing passivation of grain boundaries and interface recombination.
Implementation Method 1
The window layer allows the penetration of solar radiation to the absorber layer, where the optical energy is converted to usable electrical energy
Implementation Method 2
enhancing passivation of grain boundaries and interface recombination
Data Source
AI summary
A photovoltaic device is presented. The photovoltaic device includes a layer stack; and an absorber layer is disposed on the layer stack. The absorber layer comprises selenium, wherein an atomic concentration of selenium varies across a thickness of the absorber layer. The photovoltaic device is substantially free of a cadmium sulfide layer.