Aluminum Paste

Create a uniform high quality back surface field (BSF) with Targray's Al Paste

Giga Solar’s back side aluminum paste provides an excellent back surface field for mono and multi-crystalline silicon solar cells. The paste is designed for excellent efficiency, low bowing, high material compatibility, better adhesion strength and wide process window.

Product Benefits

• Excellent back surface field formation leading to high efficiency
• Low bowing (<1.5mm for 180um thickness wafer)
• Compatible with mono and multi-crystalline wafers and back side silver paste
• Excellent adhesion quality (>3N/cm)
• Co-fireable with back side and front side Ag pastes
• Wide process window with silver front side paste
• RoHS compliant
• Pb free

Typical Properties
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Rheology	Thixotropic, screen printable paste
Viscosity (1)	30±10 kcps
Fineness of grind	5 ~ 10 μm
Shelf Life (at 25 °C)	6 months
Sheet resistivity	<15 mΩ / sq. at 30 μm
Appearance	Silver gray
Wafer Types	Mono and multi-crystalline
Solids Content	70 ~ 80%
(1) Viscosity measured with Brookfield DV-II+CPC, #51 spindle, 38.4 sec-1, 10 rpm / 1 min, 25 °C.

Processing Summary
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Application	Standard screen print process
Screen Mesh / Emulsion Thickness	200, 250, 280 mesh / 15-25 μm
Printing	1.4±0.1 g for 6” poly crystalline
	0.9±0.1 g for 5” mono crystalline
Drying	2 min at 200-200-230 °C, 3 zone
Firing	Furnace	Infrared
	Belt Speed	220 IPM
	Set Points	Dryer 1 - 3: 300, 320, 340 °C
		Furnace 1 - 6: 550, 600, 650, 720, 865, 910 °C
	Peak Firing Temp.	750 - 800 °C or 780 - 850 °C

Typical Firing Profile

Storage Methods

• Keep the containers in a tightly sealed condition and store in a clean, dry, stable enviornment at room temperature <30 °C, relative humidity <70% RH
• Please store and use in a cleaning room after opening the container
• Shelf life of materials in unopened condition is six months from the date of shipment
• Mix thoroughly before using

Customized Al Paste solutions

Targray offers a variety of standard formulations or tailor-made Al paste solutions for optimal concordance with your needs. Consult one of our expert PV materials engineers for help identifying the best Al BSF paste for your application.

Characteristics and Benefits of High Performance Aluminum Paste

A typical aluminum paste contains metal powders, glasses and additives mixed in an organic medium. The Al Paste variables such as metal powder, glass chemistry and additives have an influence on electrical performance, wafer bowing and solar cell adhesion.

Increased electrical efficiency is typically not associated with Aluminum Paste, but many customers have seen up to 0.1% efficiency increase with our paste due to improved back-surface-field (BSF) strength.

Another important performance characteristic of Aluminum Paste is its impact on wafer bowing. As the industry pushed towards thinner wafers to reduce material costs, too much bowing will cause cell cracking and breakages. A cracked solar cell typically exhibits lower electrical efficiency and will results in more B-grade cells being produced in the cell manufacturing line. Broken cells create line stoppages, are resource intensive, and can noticeably affect cell production throughput. Our paste has excellent bowing performance on 200um, 180um and even 150um wafer thicknesses.

Finally, adhesion is heavily influenced by Aluminum Paste. Adhesion is a property that is important for module manufacturers as a solar cell must be able to withstand 1000 to 3000 hours of temperature and humidity cycling. If a solar cell’s adhesion to the backsheet is poor, it is more likely to move and put mechanical strain on the interconnect matrix in the solar module, thus reducing the module electricity output significantly. Typically, cell manufacturers evaluate adhesion after the solar cell has been fired with a tape test to qualitatively measure how much aluminum residue sticks to the tape. To evaluate adhesion in the module, a solar cell is put in a mini or full module with the backsheet and the encapsulant. A small strip of backsheet is cut in order to quantify how much force is necessary to peel off the backsheet from the backside of the solar cell covered with Aluminum Paste.