Major breakthrough for plastic solar panels could help improve cost efficiency

Scientists at the University of Montreal and their international collaborators successfully figured out how light beams excite the chemicals in plastic solar panels–enabling them to produce charge.

Why is this important?

Well, they claim this is the ‘holy grail’ to understanding the fundamental mechanistic workings (in molecular detail) of the process by which solar cells convert sunlight into energy.

The research has been published in the journal Nature Communications titled “Direct observation of ultrafast long-range charge separation at polymer–fullerene heterojunctions“.

But what are ‘plastic’ solar cells, and why do we care?

Plastic solar cells are flexible thin film solar cells made of polymer materials. Polymers, can be described as large molecules with repeating structural carbon based chains (units)–they are also known as organic solar cells.

Among the various photovoltaic technologies, polymer (plastic) solar cells offer unique attractions and opportunities. These solar cells contain Earth-abundant and environmentally benign materials, can be made flexible and lightweight, and can be fabricated using roll-to-roll technologies similar to how newspapers are printed. But the challenge has been improving the cells’ power-conversion efficiency.

This breakthrough is a big deal as understanding how ‘plastic’ solar panels work, helps open up more opportunities to study their cost efficiency which could lead to a wider use of the technology.

Applications of these solar panels would be a lot cheaper and abundant than silicon based solar cells. They could be ‘printed’ in a flexible material and easily applied to most surfaces such as walls or windows.

“Our study is a big breakthrough as we are the first to observe how the cloud of electrons on the semiconductor polymer moves while the electric charges are generated,” the study’s first author, Françoise Provencher of the University of Montreal told a Vice reporter.

“The classic scenario happens in 4 steps:
(1) the donor molecule is first excited by the light,
(2) then it transfers an electron to a nearby acceptor molecule to form an electron-hole pair (a hole is a positive charge that is created by the absence of the electron on the polymer),
(3) then the electron-hole pair separates into free charges and
(4) they create electricity as they move away,” she said.

“The big surprise is that our experiment shows that it happens all at once in the system that we studied.”

Which is all a little wonky—but the takeaway is that solar researchers used to worry that if that electron-hole pair didn’t separate right, it would put a hard limit on the efficiency of plastic solar. But it does. Which means the sky’s the limit for plastic solar. Okay, not quite the sky—the efficiency is still expected to be less than the silicon based panels, but perhaps not by enough to matter, when costs and ease of use come into play.

Current estimations for the thermodynamic limit of the efficiency of organic solar cells are around 22 to 27 percent. For comparison, silicon solar cells have a thermodynamic efficiency limit of 33 percent, which is not that much higher. The goal of the community is to reach 20 percent, but a major breakthrough in understanding is required to come up with the right materials design rules, and this research is an important step towards this.