Double-Sided Solar Cell Front Fingering Without Junction Damage
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Solution Overview
Problem
Conventional double-sided solar cells, particularly TOPCon cells, suffer from low open circuit voltage and low conversion efficiency due to the use of high-content glass powder in silver-containing pastes that damage the pn junction during the formation of front electrodes.
Innovation Solution
A method is introduced where an opening is provided through the front passivation and anti-reflection layers to allow direct contact of a non-fire-through paste with the P-type doped layer, reducing glass powder content and avoiding junction damage, thereby forming a non-fire-through front finger with reduced contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-content glass powder paste is used for screen printing front electrodes, then the paste can effectively form conductive paths, but the glass powder damages the pn junction during sintering, reducing open circuit voltage and conversion efficiency
Solution Approach 1:
The front electrode is segmented into two parts: a non-fire-through paste applied directly on the pn junction (without glass powder or with minimal glass powder ≤1.5%) and a fire-through paste applied on the passivation layer (with normal glass powder content). This segmentation allows the pn junction area to be protected from glass powder damage while maintaining effective electrical contact through the non-fire-through paste.
Solution Approach 2:
Different paste compositions are used for different regions: the non-fire-through paste with low or no glass powder is applied locally on the pn junction to avoid damage, while the fire-through paste with normal glass powder content is applied on the passivation layer for effective sintering and conductive path formation. This local quality differentiation resolves the contradiction between needing glass powder for conductivity and avoiding it for junction protection.
2Productivity
If conventional screen printing is used with printing path from back silver busbar to front silver-aluminum fine grid, then the manufacturing process is simple, but the contact resistance is high and conversion efficiency is low
Solution Approach 1:
The non-fire-through paste is applied preliminarily on the pn junction before the fire-through paste is applied on the passivation layer. This preliminary action ensures that the pn junction area is first covered with a paste that will not damage the junction during sintering, and then the fire-through paste is added to establish good electrical contact through the passivation layer.
3Productivity
If aluminum-silicon alloy is formed during sintering, then the paste adheres well to the substrate, but the contact barrier increases, reducing conversion efficiency
Solution Approach 1:
The electrode formation is segmented into two layers with different functions: the non-fire-through paste layer that prevents aluminum-silicon alloy formation and maintains low contact resistance, and the fire-through paste layer that provides adhesion and conductive paths. This segmentation allows avoiding the harmful aluminum-silicon alloy formation while maintaining good electrical contact.
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 enhances open circuit voltage and conversion efficiency by minimizing junction damage and contact resistance, resulting in improved performance of double-sided solar cells.
Implementation Method 1
coating a non-fire-through paste in contact with the P-type doped layer through the opening, sintering the paste, to form the front finger
Implementation Method 2
providing the opening corresponding to the front finger on the front surface of the semi-finished product using laser ablation
Data Source
AI summary
In one aspect, a preparation method for a double-sided solar cell includes: preparing a semi-finished product of the double-sided solar cell, the semi-finished product including a silicon wafer, and a P-type doped layer, a front passivation layer, and a front anti-reflection layer that are sequentially formed on a front surface of the silicon wafer; providing an opening corresponding to a front finger on a front surface of the semi-finished product, the opening extending through the front anti-reflection layer and the front passivation layer in sequence and exposing a surface of the P-type doped layer; and coating a non-fire-through paste in contact with the P-type doped layer through the opening, sintering the paste, to form the front finger. This preparation method can increase the open circuit voltage of the double-sided solar cell, and improve the conversion efficiency of double-sided solar cell.