Solar Cell Back Electrode Paste Composition Suppressing Substrate Warpage
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Solution Overview
Problem
The reduction in thickness of silicon substrates for solar cells leads to deformation issues like warpage during the formation of aluminum electrodes due to thermal expansion coefficient differences, affecting the production cost and appearance of solar cells.
Innovation Solution
A paste composition containing aluminum powder, glass powder, and a composite powder of titanium oxide coated with an organic or inorganic silicon compound is used to form a film-shaped aluminum electrode, with the composite powder ratio between 0.45% to 1% by mass, which suppresses warpage and foreign object formation while maintaining high solar cell characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If the thickness of silicon substrate is reduced to lower production cost and module size, then manufacturing cost is reduced, but warpage and deformation occur during firing due to thermal expansion coefficient difference
Solution Approach 1:
A paste composition is introduced as an intermediary layer between the aluminum electrode and the silicon substrate. This paste contains glass powder and organic/inorganic compounds that act as buffering agents during firing, absorbing thermal stress and preventing direct transmission of thermal expansion forces to the thin substrate, thereby suppressing warpage while enabling reduced substrate thickness
Solution Approach 2:
The chemical composition parameters of the paste are specifically optimized: glass powder content is set at 5-50 mass% and organic/inorganic compound content at 1-20 mass%. These parameter changes create a paste formulation that provides adequate thermal stress buffering without compromising the electrical functionality of the aluminum electrode
2Reliability
If aluminum electrode is formed on thin substrate by conventional paste, then electrical conductivity is achieved, but foreign objects and blisters form on electrode surface
Solution Approach 1:
The paste composition acts as an intermediary barrier layer that prevents direct contact and reaction between the aluminum electrode and silicon substrate during firing. The glass powder and organic/inorganic compounds in the paste suppress formation of aluminum silicate and other foreign objects, while still allowing aluminum to diffuse into the substrate to create the necessary p+ layer for electrical conductivity
Solution Approach 2:
By controlling the glass powder content at 5-50 mass% and organic/inorganic compound content at 1-20 mass%, the paste formulation achieves optimal balance: sufficient buffering to prevent foreign object formation and blisters, while maintaining adequate aluminum diffusion for forming the conductive p+ layer at the Al-Si interface
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 effectively reduces substrate warpage and prevents foreign object occurrence, maintaining excellent solar cell characteristics and appearance, with the short-circuit current exceeding 8.0 A and warpage reduction by 10-20% compared to conventional methods.
Implementation Method 1
deformation such as warpage or bend in the silicon substrate (wafer) itself during firing for forming the aluminum electrode 20 by a difference in thermal expansion coefficient between the substrate 11 itself and the aluminum electrode 20
Implementation Method 2
aluminum is diffused into the p-type silicon substrate (p-Si layer) 11 and a p+ layer 24 is formed
Data Source
AI summary
A paste composition for forming a back surface electrode of a solar cell 10 provided by the present invention contains, as solid matter, an aluminum powder, a glass powder, and a composite powder composed of a granular composite material of titanium oxide and an organic or inorganic compound containing silicon. When the total amount of the composite powder, the aluminum powder, and the glass powder is 100% by mass, the composite powder is contained in a ratio of 0.45% by mass or more and 1% by mass or less.