Dual-Paste Back Surface Field for Silicon Solar Cells
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Solution Overview
Problem
Existing aluminum pastes for crystalline silicon solar cells do not effectively enhance photovoltaic efficiency, as they fail to optimize the back surface field, leading to reduced hole-electron recombination rates and lower photovoltaic conversion efficiency.
Innovation Solution
A dual-paste system comprising Paste A and Paste B, where Paste A is a highly active back surface field paste with a lead- and bismuth-containing inorganic binder and Paste B has a zinc- and vanadium-containing inorganic binder, both with specific particle sizes and organic binder compositions, to improve adhesion and passivation, thereby increasing the thickness of the back surface field layer and reducing hole-electron recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional aluminum paste is used for back surface field, then manufacturing process is simple, but photovoltaic conversion efficiency is low
Solution Approach 1:
The aluminum paste is divided into two distinct types: high-activity paste containing lead and bismuth for rapid metallurgical reaction and back surface field formation, and low-activity paste containing zinc and vanadium for passivation and adhesion. This segmentation allows each paste to be optimized for its specific function, resolving the contradiction between achieving high photovoltaic efficiency and maintaining simple manufacturing.
Solution Approach 2:
Different regions of the back surface field require different material properties. The high-activity paste is applied first to create the reactive back surface field layer, then the low-activity paste is applied to provide passivation and adhesion. This local quality differentiation enables each layer to perform its specific function optimally, improving overall photovoltaic conversion efficiency without complicating the manufacturing process beyond necessary dual-layer application.
2Speed
If aluminum powder with high activity is used, then back surface field formation is rapid, but aluminum powder agglomeration increases
Solution Approach 1:
The invention changes the chemical composition parameters of the aluminum paste by introducing specific metal elements (lead, bismuth for high activity; zinc, vanadium for low activity) and optimizing their concentrations. This parameter modification enables control over both the reactivity and aggregation behavior of aluminum powder, allowing rapid back surface field formation while minimizing agglomeration through proper compositional design.
Solution Approach 2:
The aluminum paste is formulated as a composite material containing aluminum powder combined with specific amounts of lead, bismuth, zinc, and vanadium elements, along with organic and inorganic binders. This composite structure modifies the surface properties and reactivity of aluminum powder, enabling it to maintain high activity for rapid field formation while the composite matrix prevents excessive agglomeration during application and firing.
3Reliability
If inorganic binder with low softening point is used, then paste activity is high, but passivation effect is reduced
Solution Approach 1:
The inorganic binder system is segmented into two functional components: lead-bismuth-based binder with low softening point (250-400°C) providing high activity and rapid reaction, and zinc-vanadium-based binder with high softening point (450-650°C) providing superior passivation. This segmentation resolves the contradiction by assigning opposite properties to different binder components that work together in sequence.
Solution Approach 2:
The high-activity low softening point inorganic binder (lead-bismuth) is applied first to enable rapid metallurgical reaction and back surface field formation during the initial firing stage. Subsequently, the low-activity high softening point inorganic binder (zinc-vanadium) is applied to provide enhanced passivation protection. This preliminary action sequence ensures both high paste activity for field formation and subsequent passivation quality without mutual interference.
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 dual-paste system enhances photovoltaic conversion efficiency by over 20.5% by improving adhesion, reducing aluminum powder agglomeration, and increasing the passivation of the aluminum layer, resulting in a higher open circuit voltage and antireflection effect.
Implementation Method 1
the inorganic binder used is a lead- and bismuth-containing mixture with a low softening point of 250-400° C. and a high activity
Implementation Method 2
the inorganic binder used is a zinc- and vanadium-containing mixture with a high activity and a high softening point of about 450-650° C.
Implementation Method 3
both with specific particle sizes and organic binder compositions, to improve adhesion and passivation
Implementation Method 4
Paste B is a back surface field aluminum paste with a low activity and a good passivation effect
Data Source
AI summary
An efficient back surface field paste for used crystalline silicon solar cells and its preparation method include Paste A and Paste B. Paste A comprises by weight: 50-60% aluminum powder, 2-6% inorganic binder, 10-20% organic binder, 16-26% organic solvent and 2-8% additives, and the sum of weight percentages of each component is 100%. Paste B comprises by weight: 85-90% aluminum powder, 0.1-1% inorganic binder, 1-5% organic binder, 2-8% organic solvent and 1-3% additives, and the sum of weight percentages of each component is 100%.