Sacrificial Layer Mitigates Sulfur Fluxing in CdTe Photovoltaic Devices
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Solution Overview
Problem
The CdCl2 activation treatment in photovoltaic devices can cause excessive sulfur fluxing from the window layer into the absorber layer, leading to degradation or loss of the p-n junction, especially in devices with thin window layers designed for enhanced efficiency.
Innovation Solution
A sacrificial sulfur-containing layer is introduced between the window and absorber layers to control and minimize sulfur fluxing during the CdCl2 activation treatment, allowing for more aggressive treatment conditions without compromising the p-n junction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a thin window layer is used to increase light transmission, then photo-conversion efficiency is improved, but the window layer becomes more susceptible to degradation or loss during CdCl2 activation treatment
Solution Approach 1:
A sacrificial sulfur-containing layer is introduced as an intermediary between the window layer and absorber layer. This sacrificial layer absorbs the harmful sulfur fluxing effects during CdCl2 activation treatment, protecting the thin window layer from degradation while allowing aggressive treatment conditions that improve photo-conversion efficiency.
2Productivity
If aggressive CdCl2 activation treatment is applied to reduce grain boundaries and defects, then photo-conversion efficiency is improved, but excessive sulfur fluxing from the window layer occurs causing degradation or loss of the p-n junction
Solution Approach 1:
The sacrificial sulfur-containing layer acts as a mediator that captures and contains sulfur fluxing during aggressive CdCl2 activation treatment. This allows the treatment to proceed at high temperatures and for extended periods to maximize grain growth and defect reduction without the harmful sulfur fluxing that would otherwise degrade the window layer.
Solution Approach 2:
The sacrificial layer is designed to be consumed or degraded during the activation treatment process. It serves its protective function temporarily and is then removed or integrated into the absorber layer, allowing aggressive treatment conditions without permanent damage to the device structure.
3Use of energy by moving object
If the window layer is made thinner to allow more light passage, then device efficiency is improved, but the p-n junction becomes more vulnerable to degradation during activation treatment
Solution Approach 1:
The sacrificial sulfur-containing layer serves as a protective intermediary that shields the thin window layer from sulfur fluxing damage during CdCl2 activation treatment. This enables the window layer to be kept thin for optimal light transmission while preventing the harmful effects that would otherwise occur during activation treatment.
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
This approach maintains a sufficient p-n junction, enables more aggressive CdCl2 activation conditions, reducing grain boundaries and defects, and enhances photo-conversion efficiency by controlling sulfur fluxing and promoting grain growth and defect repair.
Implementation Method 1
The anneal temperature is generally high enough and the anneal time long enough to promote recrystallization of the CdTe crystallites
Implementation Method 2
annealing the absorber layer at a particular anneal temperature, for example about 400° C. to about 420° C., for a particular anneal time
Implementation Method 3
The CdCl2 and the heat from the CdCl2 activation treatment, while being beneficial in reducing the number of defective grain boundaries in the absorber layer may also promote chemical fluxing. Fluxing occurs when a chemical element from one layer of a photovoltaic device under fabrication, where it is in high concentration, flows into another layer where there is a low concentration
Implementation Method 4
Photovoltaic (PV) devices are PV cells or PV modules containing a plurality of PV cells or any device that converts photo-radiation or light into electricity
Data Source
AI summary
A completed photovoltaic device and method forming it are described in which fluxing of a window layer into an absorber layer is mitigated by the presence of a sacrificial fluxing layer.