Photovoltaic cells offer high visible light transparency

MIT researchers have developed a photovoltaic cell based on organic molecules that harnesses the energy of infrared light while allowing visible light to pass through.

Fitting such cells to a building’s windows could potentially enable the entire surface area of the windows to generate electricity.

Today, from half to two thirds of the cost of a traditional, thin-film solar-power system comes from installation costs and up to half of the cost of the panels themselves is for the glass and structural parts.

But the transparent photovoltaic system, developed by Vladimir Bulović, professor of electrical engineering in MIT’s Department of Electrical Engineering and Computer Science with Richard Lunt, a postdoctoral researcher, could eliminate many of those costs.

Previous attempts to create transparent solar cells have either had extremely low efficiency (less than one per cent of incoming solar radiation is converted to electricity), or have blocked too much light to be practical for use in windows.

But the MIT researchers were able to find a specific chemical formulation for their cells that, when combined with partially infrared-reflective coatings, gives both high visible light transparency and much better efficiency than earlier versions — comparable to that of non-transparent organic photovoltaic cells.

In a new building, or one where windows are being replaced, adding the transparent solar-cell material to the glass would be a relatively small incremental cost, since the cost of the glass, frames and installation would all be the same with or without the solar component, although it is too early to be able to estimate actual costs.

With double-pane windows, the photovoltaic material could be coated on one of the inner surfaces, where it would be completely protected from the weather or window washing. Only wiring connections to the window and a controller would be needed to complete the system in a home.

The work is still at a very early stage, Bulović said. So far, the researchers have achieved an efficiency of 1.7 per cent in the prototype solar cells, but they expect that with further development they should be able to reach 12 per cent, making their efficiency comparable to existing commercial solar panels.

The researchers expect that the technology could become a practical commercial product within a decade.