EET

Efficiency Boost for Solar Cells

Photovoltaic solar cells may be getting more efficient thanks to a couple of recent developments in cell fabrication. First, DuPont and Applied Materials, Inc. have developed multiple printing technology that is expected to increase the absolute efficiency of crystalline silicon (c-Si) photovoltaic (PV) solar cells. Photovoltaic metallization pastes are screen printed onto the surface of solar cells in a pattern of grid lines which serve to collect electricity produced by the cell and transport it out. To maximize efficiency in the solar cell, the multiple printing technology will reduce the shadowing effect of wide grid lines on solar cells and improve electrical conductivity.

DuPont Solamet photovoltaic metallization pastes are designed for use on devices that incorporate a Transparent Conductive Oxide. They promote the precise printing of narrower and taller grid lines in two or more layers. In addition to demanding precise alignment of the patterning system, multiple printing requires the paste be finely tuned to perform consistently during all printing passes.

The pastes are being used in Applied's Baccini Esatto Technology, a high precision, multi-step screen printing technique for Applied's Baccini back-end solar cell processing systems. The Esatto Technology is designed to increase the efficiency of crystalline silicon (c-Si) solar cells by double-printing metal line deposition and has been shown to raise absolute cell efficiency by as much as 0.5%. The result of several proprietary hardware and software innovations including high resolution imaging, screen alignment, and advanced process control, the Esatto Technology allows multiple layers of different materials to be overlaid with better than ±15 µm repeatability.

On another front, Honeywell has devised a transparent coating material called SolarC that improves the light transmittance through the glass that covers PV panels, thus increasing the PV module efficiency and power output. This coating also significantly reduces glare from the glass, allowing the PV panels to better blend with surroundings.

Most commercially available PV panels today lose approximately 4% of their potential power output from light reflecting off the front surface of the cover glass. The SolarC coating is said to reduce reflection significantly, so more light reaches the solar cell. While use of such anti-reflective coating is relatively low in the PV industry today, it is expected to become the industry norm over the next few years, according to major PV manufacturers.

Honeywell's liquid-based coating can be used by all common types of PV modules. It's also compatible with many coating processes, including spray, roller, curtain, slot-die and spin-on coating. It boosts transmission by 4% at 550 nm and has demonstrated a good response from 350 through 1,100 nm.

The coating has been further optimized to prevent dust accumulation. The reason: Solar panels lose on average 7% of their power output from particulate contamination, according to the California Energy Commission.

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