Local Back Electrode Aluminum Paste for PERC Solar Cells
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Solution Overview
Problem
Current methods for forming back electrodes in crystalline silicon solar cells, such as laser drilling and chemical etching, are costly and can damage the passivation film, leading to increased current leakage and reduced conversion efficiency, especially when using screen printing methods with silicon nitride films.
Innovation Solution
A high-efficiency back electrode local aluminum paste composed of 70-85% aluminum powder, 1-30% organic carrier, 0.1-10% inorganic binder, and 0.1-1% auxiliary conductive additive, with alloy powders like aluminum-zinc or silver-aluminum, applied using a 400 mesh screen printing process followed by sintering at 700-800°C to form a dense and homogeneous BSF film, minimizing passivation film damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If screen printing method is used to form back electrode on silicon nitride film, then manufacturing cost is reduced and ease of manufacture is improved, but aluminum paste cannot penetrate the silicon nitride film effectively, causing poor ohmic contact and increased current leakage
Solution Approach 1:
The patent modifies the chemical composition parameters of aluminum paste by adding specific elements (Ga, Ge, In, Sn, Pb, Bi, Se, Te) to change its reactivity and penetration capability through silicon nitride film, enabling effective ohmic contact while maintaining screen printing manufacturing method
Solution Approach 2:
The patent creates a composite aluminum paste material combining aluminum powder with multiple alloying elements and organic/inorganic binders, where the composite structure provides both penetration capability through the passivation film and reliable ohmic contact properties
2Reliability
If laser drilling method is used to prepare back contact, then ohmic contact quality is improved, but equipment complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent extracts the essential function of laser drilling (creating penetration paths through silicon nitride film) and replaces it with a chemically-active aluminum paste that can penetrate the film through its own reactivity, eliminating the need for complex laser drilling equipment
Solution Approach 2:
The patent replaces the mechanical/thermal laser drilling system with a chemical reaction-based penetration mechanism, where the aluminum paste chemically reacts with and penetrates the silicon nitride film, substituting a simple screen printing process for complex laser equipment
3Reliability
If chemical etching method is used to prepare back contact, then ohmic contact quality is improved, but environmental pollution increases
Solution Approach 1:
The patent converts the normally harmful chemical etching process into a beneficial self-contained reaction where the aluminum paste itself performs the etching function locally at the contact points, eliminating the need for separate chemical etching steps and their associated pollution
4Quantity of substance
If thinner silicon wafers are used to reduce material cost, then silicon raw material cost is reduced, but surface composite velocity increases and cell efficiency decreases
Solution Approach 1:
The patent applies local quality enhancement by creating highly-effective local back contact regions with improved ohmic contact properties, which compensates for the reduced bulk silicon thickness and maintains overall cell efficiency despite using thinner wafers
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
The solution achieves a conversion efficiency of over 20.7% with reduced current leakage and improved ohmic contact, enabling cost-effective mass production of PERC silicon solar cells with enhanced performance and durability.
Implementation Method 1
Chemical etching method, mainly using silicon paste on the composite passivated film to screen-print the silicon paste film with dot-contact pattern before etching by chemical liquid to remove the portions not covered by silicon paste film on the composite passivated film
Implementation Method 2
followed by sintering at 700-800°C to form a dense and homogeneous BSF film
Implementation Method 3
applied using a 400 mesh screen printing process
Data Source
AI summary
A high-efficiency back electrode local aluminum paste crystalline silicon solar cell is composed of the following components proportioned to weights: 70-85 of parts powder, 1-30 parts of organic carrier, 0.1-10 parts of inorganic binder, 0.1-1 parts of auxiliary conductive additives. The aluminum paste is mainly used to manufacture the passivated emitter and back electrode of silicon solar cell with dot or linear contact on rear surface. PERC aluminum paste printed on the passivated film of the silicon wafer with dot-opening or linear-opening is dried and sintered.