Dielectric Back Reflective Coating for Solar Cells
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Solution Overview
Problem
The challenge is to economically produce a solar cell with a dielectric reflective coating on the back that reduces charge carrier recombination rates while preventing the firing-through of pastes containing glass components, which is costly and affects the adhesion of metallic contacts.
Innovation Solution
A method involving a layer stack of dielectric layers, specifically silicon oxide and silicon nitride, is applied to the solar cell substrate and heated to at least 700°C for densification, enhancing resistivity to glass-containing pastes, and local openings are formed for metallic contact formation, allowing for efficient dielectric passivation and reduced recombination rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dielectric layers are applied to the back of the solar cell substrate, then charge carrier recombination rates are reduced, but the pastes containing glass components fire through the dielectric layers during the firing process
Solution Approach 1:
The dielectric layers are subjected to a preliminary densification treatment by heating to a temperature of at least 700°C for at least 5 minutes before the metallic paste is applied. This preliminary action increases the resistivity of the dielectric layers, preventing the paste from firing through during subsequent processing while maintaining the low recombination rate benefit
Solution Approach 2:
The physical and chemical parameters of the dielectric layers are changed through thermal densification. By heating to high temperature (≥700°C) for extended duration (≥5 minutes), the density and resistivity of the dielectric layers are increased, transforming them from a state that allows paste penetration to one that resists it
2Object-generated harmful factors
If the dielectric layers are made thicker to prevent firing-through, then paste penetration is reduced, but production costs increase substantially
Solution Approach 1:
Instead of increasing the thickness parameter of the dielectric layers, the invention changes the density and resistivity parameters through thermal treatment. This allows maintaining thin layer thickness (cost-effective) while achieving high resistivity (paste protection) through parameter transformation rather than dimensional increase
3Ease of manufacture
If standard printing processes are used to apply metallic paste, then production cost is reduced, but the paste fires through the dielectric layers and adhesion is compromised
Solution Approach 1:
The dielectric layers undergo preliminary densification heating before paste application. This prepares the dielectric layers in advance to resist paste penetration during standard printing and firing processes, enabling the use of cost-effective standard processes without compromising adhesion
Solution Approach 2:
The densified dielectric layers act as an intermediary barrier between the metallic paste and the solar cell substrate. This intermediate layer prevents harmful paste penetration while allowing controlled contact through local openings, enabling standard printing processes to work effectively
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 results in low charge carrier recombination rates and prevents the firing-through of glass-containing pastes, making the production process more economical and improving the efficiency of solar cells by enhancing the adhesion and conductivity of metallic contacts.
Implementation Method 1
These are designed in such a way that light quanta striking the dielectric layers are reflected by the total-reflection effect
Implementation Method 2
the layer stack is heated and held at temperatures of at least 700° C. for a period of at least 5 minutes
Data Source
AI summary
In a method for producing a solar cell, a layer stack of dielectric layers is applied to a back of a solar cell substrate and the layer stack is heated and is held at temperatures of at least 700° C. during a time period of at least 5 minutes. The novel solar cell has a layer stack of dielectric layers on its back. At least one of the dielectric layers of the layer stack is densified so that its resistivity to firing-through of pastes with glass components is enhanced.