Ammonium Sulfide Passivation for Chalcogenide Solar Cells
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Solution Overview
Problem
Existing methods for cleaning and passivating chalcogenide semiconductor layers, such as CIGS and CZTS, often use toxic chemicals like potassium cyanide or require heating, which are not suitable for industrial processing and can lead to reduced photovoltaic conversion efficiencies due to the presence of secondary phases and defects.
Innovation Solution
A method involving exposure to an ammonium sulfide-containing ambient at ambient temperature to chemically remove secondary phases and passivate the chalcogenide layers, using a less toxic and safer chemical process that simultaneously cleans and passivates the surfaces without heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If potassium cyanide (KCN) solution is used to remove copper selenide impurities, then the cleaning effectiveness is improved, but the safety and environmental friendliness deteriorate due to high toxicity
Solution Approach 1:
The patent changes the chemical composition parameter from toxic KCN to less toxic ammonium sulfide ((NH4)2S), maintaining cleaning effectiveness while improving safety. The chemical formulation is modified to achieve the same etching function without the harmful cyanide component.
Solution Approach 2:
The patent uses ammonium sulfide as a safer, more environmentally friendly alternative to KCN. While both chemicals serve the same function, ammonium sulfide is less persistent in the environment and safer to handle, effectively replacing a hazardous material with a more benign one.
2Manufacturing precision
If thermal treatment is applied to remove secondary phases, then the cleaning effectiveness is improved, but the structural integrity deteriorates due to stress and cracks from thermal expansion differences
Solution Approach 1:
The patent replaces thermal treatment (thermal energy) with chemical treatment (chemical reaction). Instead of using heat to remove secondary phases, which causes thermal stress and cracking, the patent uses ammonium sulfide solution to chemically etch and remove impurities at ambient temperature, preserving the structural integrity of the chalcogenide layer.
Solution Approach 2:
The patent changes the treatment parameter from thermal energy to chemical energy. The process temperature is reduced from elevated thermal treatment temperatures to ambient temperature, eliminating thermal stress while maintaining cleaning effectiveness through chemical etching.
3Stability of the object's composition
If copper-rich layer composition is used to enhance grain growth, then the material quality is improved, but the electrical performance deteriorates due to increased shunt conductance from Cu x Se phase formation
Solution Approach 1:
The patent applies preliminary chemical treatment with ammonium sulfide solution before device fabrication or operation. This pre-treatment removes copper selenide secondary phases that would otherwise form during copper-rich processing, preventing future shunt conductance problems while allowing the copper-rich composition to be used for enhanced grain growth.
Solution Approach 2:
The patent selectively removes the harmful Cu x Se secondary phase from the copper-rich chalcogenide layer. By extracting this specific impurity phase while preserving the main chalcogenide material, the patent enables the benefits of copper-rich composition (enhanced grain growth) without the detrimental effects (shunt conductance).
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 method effectively removes secondary phases and enhances minority carrier lifetimes, leading to improved photovoltaic cell efficiencies and current-voltage characteristics, while using a safer and more environmentally friendly chemical process.
Implementation Method 1
contacting the chalcogenide layer with an ammonium sulfide ((NH 4 ) 2 S) containing liquid, thereby removing impurities and/or secondary phases from the chalcogenide layer
Implementation Method 2
chemically passivating chalcogenide layers... Passivation of these defects may lead to longer minority carrier lifetimes
Data Source
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AI summary
A method is disclosed for chemically cleaning and passivating a chalcogenide layer, wherein the method comprises contacting the chalcogenide layer with an ammonium sulfide containing ambient. Further, a method is disclosed for fabricating a photovoltaic cell, wherein the method comprises: providing a chalcogenide semiconductor layer (12) on a substrate (10); contacting the chalcogenide semiconductor layer (12) with an ammonium sulfide ((NH4)2S) containing ambient, thereby removing impurities from and passivating the chalcogenide semiconductor layer; and afterwards providing a buffer layer (13) on the chalcogenide semiconductor layer (12).