Photovoltaic Cell Contact Resistivity Control via Controlled Cooling
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Solution Overview
Problem
The existing manufacturing processes for electrical contacts in photovoltaic cells, particularly those using transparent conductive oxide layers, face challenges due to high thermal annealing requirements and ambient air exposure, which lead to increased resistivity of the oxide layers.
Innovation Solution
A method involving a heat treatment under ambient air with controlled cooling to manage the temperature gradient, allowing for slow cooling of the photovoltaic cell before exposure to ambient air, thereby minimizing the increase in resistivity of the conductive transparent oxide layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heat treatment is applied under ambient air atmosphere, then the manufacturing process is simplified and does not require controlled atmosphere equipment, but the resistivity of the transparent conductive oxide layer increases considerably
Solution Approach 1:
The patent applies a preliminary slow cooling step (cooling at a rate of 1-100°C per minute) after heat treatment under ambient air before exposing the cell to ambient air. This preliminary action prevents the formation of oxygen vacancies that would otherwise occur during rapid cooling, thereby maintaining low resistivity while allowing the use of simple ambient air atmosphere during manufacturing
2Productivity
If the photovoltaic cell is quickly removed from the enclosure after heat treatment, then productivity is improved, but the resistivity of the transparent conductive oxide layer increases due to oxygen exposure
Solution Approach 1:
The patent introduces a preliminary controlled cooling phase within the enclosure before removing the cell to ambient air. This preliminary action of slow cooling (1-100°C per minute) prepares the transparent conductive oxide layer by preventing oxygen vacancy formation, allowing subsequent rapid removal without resistivity increase
Solution Approach 2:
The patent changes the temperature parameter control during the cooling phase, specifying a cooling rate of 1-100°C per minute. This parameter change in cooling rate prevents thermal shock and oxygen vacancy formation, resolving the contradiction between quick removal for productivity and slow cooling for conductivity maintenance
3Manufacturing precision
If high temperature thermal annealing (800-900°C) is applied to form electrical contacts, then the screen printing paste is properly cured, but the transparent conductive oxide layer becomes incompatible with electrical contact formation due to resistivity increase
Solution Approach 1:
The patent changes the cooling rate parameter to 1-100°C per minute after high temperature heat treatment. This parameter change in cooling rate maintains the benefits of high temperature curing for electrical contact formation while preventing the resistivity increase that would otherwise occur, thus resolving the incompatibility issue
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 effectively reduces the resistivity of the transparent conductive oxide layer, preventing the prohibitive increase associated with quick exposure to ambient air after heat treatment, while maintaining the process under uncontrolled atmospheric conditions.
Implementation Method 1
apply a heat treatment to the photovoltaic cell, at the curing temperature, in an enclosure surrounded by ambient air
Implementation Method 2
cool the enclosure for a period determined according to the curing temperature, so as to subject the photovoltaic cell to a temperature gradient less than or equal to 100°C per minute
Implementation Method 3
the screen printing paste has a curing temperature... apply a heat treatment to the photovoltaic cell, at the curing temperature
Data Source
Figure 1~2b
Figure 3~5
AI summary
This process comprises the following successive steps: a) providing a photovoltaic cell (1) comprising: - a layer (2) of conductive transparent oxide; - a screen printing paste (3), electrically conductive, and formed on the layer (2) of conductive transparent oxide, the screen printing paste (3) having a curing temperature; b) applying a heat treatment to the photovoltaic cell (1), at the curing temperature, in an enclosure (4) surrounded by ambient air, and under an atmosphere comprising ambient air; c) cooling the enclosure (4) for a time determined according to the curing temperature, so as to subject the photovoltaic cell (1) to a temperature gradient less than or equal to 100°C per minute; d) removing the photovoltaic cell (1) from the enclosure (4) so as to expose the photovoltaic cell (1) to ambient air.