CdTe Absorber Layer Grading for Reduced Reflection Loss
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Solution Overview
Problem
CdTe based thin film solar cells face efficiency limitations due to high refractive index differences at the interface between the glass substrate and the CdTe absorber layer, leading to light reflection and sub-bandgap defects from doping elements, which degrade photovoltaic performance.
Innovation Solution
A method for manufacturing CdTe based thin film solar cells with a graded refractive index profile within the absorber layer, using a doped CdTe layer stack with vanadium as the first doping element and a second doping element to create a smooth transition in refractive index, reducing sub-bandgap defects and improving light coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a sudden transition from a first material to a second material is used in the absorber layer, then material deposition is simplified, but light scattering is insufficient and device efficiency is limited
Solution Approach 1:
The patent applies local quality by creating a graded refractive index profile where the refractive index changes gradually from one value to another across the absorber layer thickness. This is achieved by varying the composition ratio of first and second materials at different positions (depths) within the absorber layer, with each local region having optimized material composition to provide appropriate light scattering while maintaining manufacturing simplicity through sequential deposition.
2Loss of energy
If a graded refractive index profile is implemented, then light scattering and device efficiency are improved, but material deposition complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the absorber layer into multiple sub-layers or segments, where each segment contains a specific ratio of first and second materials. This segmentation approach allows the graded refractive index profile to be constructed through sequential deposition of layers with progressively changing composition ratios, making the complex graded structure achievable through repeated application of simpler deposition processes rather than requiring complex in-situ composition control.
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 graded refractive index profile enhances light coupling and reduces sub-bandgap defects, resulting in higher open circuit voltage and improved photovoltaic efficiency.
Implementation Method 1
the absorber layer has a graded refractive index profile from the first interface to the second interface, thereby improving light scattering
Implementation Method 2
A photovoltaic (PV) device comprises a substrate, a buffer layer, a meso-super-network structure, a transparent conductive oxide layer, and a metal electrode
Data Source
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AI summary
A method for manufacturing a CdTe based thin film solar cell device with a graded refractive index profile within the CdTe-based absorber layer. The method comprises the following steps: a) providing a transparent substrate comprising a front electrode, b) forming a doped CdTe based absorber layer on the substrate, c) performing an activation treatment after step b). The doped CdTe based absorber layer in step b) is formed as a doped CdTe based absorber layer stack comprising a first and a second layer. The first layer is formed as a first doping element containing layer comprising vanadium as the first doping element by depositing a first doping element-rich layer and subsequently depositing a CdSe layer or a CdSeTe layer, or by depositing a CdSe layer or a CdSeTe layer each doped with the first doping element. The second layer is formed by depositing a CdTe layer. A CdTe based thin film solar cell device with a graded refractive index profile.