High Performance Solar Pastes & Adhesives
Improve efficiency, fill-factor, and conductivity with ACI’s cavitated materials.
Our Conductive Materials for Solar Applications
Front side gridlines with better contact resistance, fill factors, and efficiency. Materials are customized to specific customer needs and process conditions.
Electrically Conductive Adhesives
Improve reliability by connecting cells with flexible adhesives to reduce thermomechanical fatigue. Customized formulations available.
Solar Cell Anatomy
Gridline Conductive Trace
Cavitation evenly disperses the constituent materials of the solar ink/pastes, including conductive silver and glass frit, into an organic vehicle. The material is then screen printed onto the surface of the solar cell and fired. This even distribution of silver and glass enables better rheology and reduced slump, leading to less shadowing of the active surface. It also creates even distribution of the glass frit so that penetration into the emitter layer is of more uniform depth and spacing, which decreases the contact resistance. Lastly, the superior dispersion improves the bulk conductivity of the gridline, which decreases the series resistance and improves performance. Specific formulations are tailored to customer requirements.
Flexible Conductive Adhesive
Individual solar cells are linked together to create a panel and generate current.. These electrical connections can be subject to mechanical fatigue over many heating cycles, and soldered/rigidly bonded wire connections can be reliability problems. ACI offers flexible conductive adhesives as an alternative connection strategy that limits the buildup of stresses due to thermal expansion and can lower fatigue-related reliability issues.
*Note that this is not shown in the figure.
Putting it All Together
Sunlight penetrates into the cell with the assistance of an anti-reflective coating. The absorption of incident photons from the sunlight will generate electron-hole pairs in the body of the cell. These charge carriers are separated and collected by the front side gridline and the back contact, creating a current. Note that the sun cannot pass through the silver conductive gridlines so minimizing the real estate covered by the gridlines by maximizing the bulk conductivity and aspect ratio (make them taller and less wide) will greatly affect the ultimate performance.
The carriers are separated by the action of the electric field existing at the p-n junction with the electrons being excited to a higher energy state in the emitter layer where they are collected by the silver gridlines (front contact). The holes move toward the rear contact where a back surface field creates a highly doped region to minimize the impact of rear surface recombination.
The current is generated by connecting the front and rear contacts.
The cell performance is largely determined by the quality of the cell emitter but it is also greatly impacted by the conductive gridline characteristics. As mentioned earlier, the primary constituents are silver powders/flakes and fine glass powder dispersed in a screen-printing organic medium. With the glass powder being typically around only 2 weight % of the entire composition, it is extremely important to have it well dispersed being a minor but critical component.
The glass performs many functions that determine the cell performance: (1) the glass must etch through the anti-reflective coating (ARC) and penetrate into the emitter layer at a uniform depth. If it does not penetrate the ARC then there is no path to collect the current. If it penetrates too far and etches through the thin (70nm) emitter layer, then the cell is shunted. Therefore, a uniform dispersion at the ARC interface and narrow particle size distribution to create uniform melting of the glass will result in ideal penetration depth during a specified firing profile. Our cavitation process provides this necessary type dispersion to achieve ideal penetration.
Furthermore, the glass will carry the silver into the emitter region where it will form conductive spikes or contacts to collect the current and create the lowest possible contact resistance. With respect to the silver gridlines, the higher the bulk conductivity for a given cross section, the series resistance will be minimized and the resultant cell performance will be maximized with respect to efficiency and other cell figures of merit.