1、 Profile design and surface treatment of clamping surface

Stacked tile solar cells adopt a structure in which multiple cells are tightly arranged and the edges overlap with each other, and their force surface is not flat but has specific curved features. Therefore, the clamping surface of the fixture must be precisely designed to match the contact area of the battery cell edge. Research has shown that when the adhesion between the clamping surface and the edge of the battery cell reaches over 95%, the variability of test data can be reduced by 40%. At the same time, surface treatment of the clamping surface is also extremely important. It is recommended to use fine-grained diamond spraying technology to form a uniform surface with a roughness of about 5-8 microns, which can provide sufficient friction to prevent slipping and will not cause scratches to the battery cells. The comparative data from a certain photovoltaic laboratory shows that the optimized copying fixture can improve the test repeatability from ± 3.2% to ± 1.1%.

2、 Accurate control and distribution of clamping force

Stacked tile solar cells are extremely sensitive to clamping force. Excessive clamping force may cause hidden cracks or electrode detachment inside the cell, while insufficient clamping force can cause sample slip during testing. The ideal clamping force should be controlled within a linear range of 0.8-1.2N/mm and precisely adjusted through hydraulic or servo motors. More importantly, the distribution design of clamping force, using a multi-point distributed clamping structure (usually 6-8 contact points), can more evenly distribute pressure than traditional two-point clamping. Experimental data shows that distributed clamping can reduce the stress concentration factor at the edge of battery cells from 1.8 to below 1.2, significantly reducing unexpected damage during testing. In addition, the response time of the clamping force feedback system should be less than 50ms to ensure real-time adjustment capability during dynamic testing.

3、 Thermal expansion compensation and positioning reference design

The tensile testing of stacked tile solar cells is often conducted in an environmental chamber, and temperature changes can cause thermal expansion differences between the fixture and the sample. Excellent fixture design should include a thermal expansion compensation mechanism, usually using Invar alloy (expansion coefficient less than 1 × 10 ⁻⁶/℃) as the key component material, or pre setting a thermal expansion gap of 0.05-0.1mm/mm in the structure. The design of positioning reference cannot be ignored, and at least three precision positioning pins (with tolerance controlled at H7/g6 level) should be set on the fixture to ensure the repeatability of the battery cell position within ± 0.02mm during each clamping. At the same time, the connection between the fixture and the testing machine should adopt a floating joint design to eliminate the influence of the coaxiality error of the equipment itself on the test results.

These three details may seem independent, but they are actually interrelated and together determine the reliability of the tensile testing of stacked solar cells. Only by organically integrating the three elements of copying clamping, force control distribution, and thermal compensation positioning can we obtain test data that truly reflects product performance, providing scientific basis for quality control and reliability evaluation of photovoltaic modules. With the continuous development of tile stacking technology, fixture design also needs to be continuously optimized to meet the testing needs of thinner silicon wafers and higher power components.