CdTe Solar Cell Copper Migration Control via Segmented Processing
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Solution Overview
Problem
Existing CdTe solar cell production methods face challenges in achieving high efficiency due to copper migration, which degrades cell characteristics over time, and require precise control of copper concentration and position to establish a good ohmic contact.
Innovation Solution
A method involving specific processing steps and parameters, including closed space sublimation for CdS and CdTe layers, controlled temperature treatments, copper ion introduction after applying the back contact, and artificial aging with precise illumination, along with cleaning steps using diammonium hydrogen citrate and dimethylformamide solutions, to optimize layer thickness and copper distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is introduced into the CdTe layer to establish good ohmic contact, then electrical contact quality improves, but copper migration increases causing degradation over time
Solution Approach 1:
The process is divided into distinct stages: first applying copper to the CdTe layer, then applying the back contact, and finally performing a controlled thermal treatment. This segmentation allows copper to be positioned precisely at the interface without direct contact with the back contact metal, preventing migration while maintaining electrical contact quality.
Solution Approach 2:
Copper is applied to the CdTe layer before the back contact is applied. This preliminary positioning of copper allows it to diffuse into the CdTe layer during subsequent thermal treatment, establishing good ohmic contact without requiring copper to be in direct contact with the back contact metal, thereby preventing migration.
2Stability of the object's composition
If precise control of copper concentration and position is implemented, then copper migration is reduced, but process complexity increases
Solution Approach 1:
Copper is applied to the CdTe layer before the back contact is applied. This preliminary positioning of copper allows it to diffuse into the CdTe layer during subsequent thermal treatment, establishing good ohmic contact without requiring copper to be in direct contact with the back contact metal, thereby preventing migration.
Solution Approach 2:
The process utilizes controlled thermal treatment at specific temperature ranges (150-250°C) for specific durations (10-60 minutes) to control copper diffusion. By optimizing these parameters, copper is driven into the CdTe layer to the desired depth without excessive migration, achieving precise control through parameter optimization rather than complex equipment.
3Productivity
If multiple processing steps with precise parameters are used, then solar cell efficiency improves, but manufacturing time increases
Solution Approach 1:
The copper introduction and back contact application steps are merged into a single process sequence where copper is applied first, then the back contact is applied over it. This combination eliminates the need for separate copper deposition and back contact deposition processes, reducing manufacturing time while maintaining the precision of copper positioning.
Solution Approach 2:
Copper is applied to the CdTe layer before the back contact is applied. This preliminary positioning of copper allows it to diffuse into the CdTe layer during subsequent thermal treatment, establishing good ohmic contact without requiring copper to be in direct contact with the back contact metal, thereby preventing migration.
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
Results in CdTe solar cells with efficiencies exceeding 17% and improved electrical characteristics such as open circuit voltage, fill factor, and short-circuit current, surpassing previous methods by ensuring controlled copper migration and better ohmic contact.
Implementation Method 1
Applying a CdS layer on the transparent conducting layer using closed space sublimation (CSS) technique
Implementation Method 2
Applying a CdTe layer on the CdS layer using CSS technique
Implementation Method 3
The copper may be provided to the CdTe layer as an elemental layer comprising only copper or as a dopant contained in another material or as an ion
Implementation Method 4
a temperature treatment step
Implementation Method 5
The copper may be provided to the CdTe layer as an elemental layer comprising only copper or as a dopant contained in another material or as an ion
Implementation Method 6
an artificial aging step including illumination or electric biasing after applying all layers of the solar cell
Data Source
AI summary
The present invention describes a method for producing CdTe thin-film solar cells, in which special parameters of different processing steps and a special sequence of processing steps result in improved characteristics of the produced CdTe solar cells.