Bright prospects

The first modern photovoltaic cell was created in the year 1954 by the American company Bell Laboratories. The first solar cells were made of silicon and weren't much bigger than a razor blade. They could convert around six percent of the sunlight they received into energy.

Bell’s invention kicked off the buzz around photovoltaic technology, the process of transforming sunlight directly into energy via solar cells. Today, the technology is used in everything, from small devices such as pocket calculators right up to outer space, where solar energy powers satellites.

Surging growth

Photovoltaics only have a market share of two percent in Germany, but the industry is growing rapidly. According to the German Solar Industry Association, in 2011 Germany reached a new record by producing almost 70 percent more solar energy than in the previous year.

The trend is likely to continue. In May last year, the German government voted to phase out nuclear energy as soon as possible and accelerate the move towards renewables. The goal is to double the current share of installed renewables in Germany's energy mix to 35 percent by 2020. And to reach that target, solar and wind power will need to play a significant role.

Globally, the solar energy outlook is also growing ever brighter. According to a recent study by Swiss financial institution Bank Sarasin, photovoltaic technology could generate 620 gigawatts of electricity by the year 2020 – a figure that is equivalent to the capacity of 440 major nuclear power plants.

And that jump in solar capacity would be astonishing considering that by the end of 2010, solar cells could only achieve 42 gigawatts.

Organic photovoltaics – solar cells of the future?

Silicon has dominated the solar cell industry until this point. Some 90 percent of today’s solar cells are produced with the material, says the Fraunhofer Institute for Solar Energy Systems, or ISE.

But the race to find an alternative is heating up around the world, and for good reason: silicon carries significant disadvantages. The rare earth minerals used in solar technology are expensive and toxic and it's difficult to recycle them, making the product not particularly eco-friendly. So researchers are exploring other possibilities in the hopes of finding a cost-effective and efficient alternative.

"There have always been various parallel approaches in the photovoltaics industry," Karl Leo, director of the Institute for Applied Photophysics, or IAPP says. Leo and a team of researchers are exploring organic photovoltaics or OPVs.

Unlike typical solar cells composed of semiconductors like silicon, these cells utilize carbon-based polymers such as carbonate, hydrogen and oxygen. These are found in abundance all over the world which makes them affordable as well.

Karl Leo says that organic photovoltaics opens up a wide variety of possibilities and applications. "That includes power plants, roofs or cell phones," he says.

What’s more, Leo says the cells his team is exploring are have an edge on their silicon counterparts: they are flexible and can be pasted on to practically any surface, whether it's window panes, paper, plastic or fabric.

That means it might be possible to produce handbags that can charge cell phones, or facades and windows on homes that generate energy for the people living inside. Their research has gained wide popularity, earning them the German Future Prize last year, the most prestigious honor awarded for science and innovation in the country.

Tapping

the entire spectrum

Karl Leo pointed to another technology, concentrated photovoltaics (CPV) which is considered one of the newer players on the solar energy scene.

In CPV, an array of lenses is used to focus sunlight onto small solar cells. The concentrated light improves the efficiency of the cells and reduces the amount of expensive solar cell material needed to produce a given amount of electricity.

These systems have solar cells outfitted with not one but three layers of photovoltaic materials. Each layer reacts to a different color on the light spectrum: the top layer is sensitive to blue light, the middle to green and yellow, and the last layer to infrared light.

Since the cells respond to a wide variety of colors, they are able to generate more power, transforming nearly 40 percent of the sun’s light into energy.

Silicon cells, on the other hand, only offer 20 percent efficiency, and organic solar cells offer even less at 10 percent. There is one major disadvantage to CPV though: the minerals needed are even more expensive than silicon.

Solar cells just inverted LED’s?

"Organic photovoltaics will always be less efficient than silicon cells," Karl Leo says. "But our long-term goal is to make them half as expensive."

Organic solar cells are expected to be ready for mass production in 2013 at the latest. Leo says organic solar technology has huge potential. It's not just possible to generate electricity from light, he adds, but also the other way round - to harness light from electricity.

"Solar cells are essentially just inverted light-emitting diodes (LED’s)," Leo says. The materials used to produce them may be different, but the cell structures are similar.

In other words, it might be possible that transparent solar panels on windows could generate energy during the day and then serve as lamps in the evening.

Author: Michaela Führer/ss
Editor: Sonia Phalnikar