A research team from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University has developed a way that would improve the efficiency of solar cells and make them more affordable.

A scanning electron microscope image of the rigid pillar-like bristles of the rake, which is used to apply light-harvesting polymers to a solar cell. Image credit: Zhenan BaoThe technique has the potential to double the electricity output of inexpensive solar cells by using a microscopic rake when applying light-harvesting polymers.

The researchers say that when commercialized, this advance could help make polymer solar cells more economically appealing than those made with silicon-crystal wafers.

During experimentation, the researchers found that solar cells made with the tiny rake doubled the efficiency of cells made without it and were 18% better than cells made using a microscopic straightedge blade.

“The fundamental scientific insights that come out of this work will give manufacturers a rational approach to improving their processes, rather than relying simply on trial and error,” says Zhenan Bao, a chemical engineering professor at Stanford.

In the current market, polymer-based photovoltaic cells are less expensive because they are made of materials that can be printed in place or painted, and that are flexible and require little energy to manufacture.

In this research, the polymers are painted onto a conducting surface and then forced through a slightly angled rake containing several rows of stiff microscopic pillars.

The rake is scraped along the surface at 25-100 micrometers per second. The large polymer molecules untangle and mix with each other as they bounce off and flow past the pillars, ultimately drying into tiny nanometer-sized crystals of uniform size with enhanced electrical properties, the researchers say.

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