Black Silicon Solar Cell Efficiency Doubled

While conventional solar cells can absorb a good portion of the Sun’s light, they completely miss the boat on getting anything from the infrared spectrum. But black silicon solar cells are actually designed exactly for this. A group of researchers from the Fraunhofer-Gesellschaft institute in Germany have recently succeeded in doubling solar cell efficiency of black silicon solar cells!

Infrared radiation makes up about 25% of the solar spectrum. Black silicon can absorb almost all of this, and then turn it into electricity. So, there’s quite a bit of potential to improve the efficiency of solar panels by using black silicon.

What the heck is black silicon, you ask? “Black silicon is obtained by irradiating conventional silicon under sulfur atmosphere with a femtosecond laser,” explains Dr. Stefan Kontermann, group manager of the Fraunhofer Project Group Fiber optic sensor systems at the Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut.”The surface is roughened, installed individual sulfur atoms in the silicon lattice and the material is black.” (Translations from German courtesy of Google Translate.)

So, how did the researchers boost black silicon solar cell efficiency? (Warning: science speak coming.) “We achieved this by having changed the shape of the laser pulse, with which we irradiate the silicon,” says Kontermann.

Here’s more from the Fraunhofer-Gesellschaft press release: “This allowed the scientists to solve a problem of the black silicon: While the infrared light hitting normal silicon does not have enough energy to raise the electrons in the ‘conduction band’ and thus bring in the current cycle, ie convert it into electricity, the sulfur added to the black silicon creates a sort  of intermediate step here.”

However, this intermediate step also allows electrons to jump the wrong way, resulting in lost electricity. But the researchers’ modification of the laser pulse solves this problem a bit by guiding more electrons in the right direction.

Where to go next?

The researchers’ next step is to evaluate how different shapes of laser pulses affect energy levels of the sulphur. And, eventually, the goal to create a system of algorithms that will be able to automatically identify how the laser pulse should be modified in order to achieve maximum efficiency.

The end goal is, of course, to merge the black silicon solar cells the researchers develop with existing commercial technology in order to bring a leading solar power product to market. According to the researchers, their intention is to add black silicon solar cells to conventional solar cells, creating a tendem solar cell, and thus boosting overall solar cell efficiency by about 1%.

“Furthermore, the scientists are planning a spin-off: In this company they want to market the laser system for manufacturers to expand their existing solar cell lines. They would then be able to produce the black silicon itself and build it into the cells.”

Yeah, this is all a bit over my head, but sounds interesting, and useful. Let’s hope so!

And, apparently, the research is rather highly esteemed, as this project has won an award from the “365 Places in the Land of Ideas” competition. An award ceremony is being held tomorrow (or later today for some of you), October 11, in Goslar.