Nanorods made of fullerenes improve performance of polymer solar cells

September 16, 2011

The biggest obstacle to making use of solar energy has been the excessively high price of solar cells made of inorganic semiconductors. In contrast, solar cells based on semiconducting polymers are affordable, light, thin, and flexible -- but their performance has been lacking. A team led by Chain-Shu Hsu at the National Chaio Tung University and Yuh-Lin Wang at Academia Sinica in Taiwan has now developed a new approach that uses fullerene nanorods to significantly increase the effectiveness of polymer-based solar cells. They introduce their work in the journal Angewandte Chemie.

In the photoactive layer of a solar cell, sets free. This leaves behind positively charged gaps or "holes". Electrons and holes must be separated quickly and efficiently, or they recombine and reduce the power of the solar cell. The efficiency of a solar cell thus depends on how well the resulting charge is directed away and transported to the electrodes.

In polymer , it is possible to attain more efficient charge separation through the addition of acceptors, such as , which take up electrons. One highly promising concept is to embed the acceptor molecules in a disordered matrix made of photoactive . The boundary surface between the two components is thus spread over the entire layer. This construct is known as a “bulk-hetero contact”. After charge separation, the electrons and holes are located in different molecular systems, which transport them selectively to opposite electrodes.

The problem is that the two materials are not evenly distributed. The travel pathways for the charges are thus disordered, allowing holes and electrons to encounter each other easily. In addition, charge-separated islands can occur. The solution would be an “ordered bulk-hetero contact”, a periodic structure of vertically directed, interpenetrating regions of both materials. Electrons and holes would then have straight pathways that do not cross. However, it has previously not been possible to produce any effective photolayer using this principle, because the components are not molecularly intermixed, making the electron pathways too long to produce effective charge separation.

The Taiwanese researchers decided to combine the two structural principles. By using a nano-casting process, they produced a layer of vertically oriented nanorods from a cross-linking polymeric fullerene material. The spaces between the rods were filled with a mixture made from a photoactive polymer and a fullerene. This layer ensures effective , and the interpenetration of the fullerene nanorods ensures ordered – and thus effective—charge transport. Solar cells made with this novel combined photolayer are stable and achieve amazingly high performance.

Explore further: A Polymer Solar Cell with Near-Perfect Internal Efficiency

More information: Chain-Shu Hsu, Enhanced Performance and Stability of a Polymer Solar Cell by Incorporation of Vertically Aligned, Cross-Linked Fullerene Nanorods, Angewandte Chemie International Edition, Permalink to the article:

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5 / 5 (1) Sep 16, 2011
"amazingly high" = how high exactly?
not rated yet Sep 16, 2011
"amazingly high" = how high exactly?

Yeah, c'mon physorg, how about some facts?

In spite of the lack of details, I think this fabrication technique is going to find a lot of applications, not just in solar. Using nanotubes as a medium for controlling interactions between materials is going to be big. They'll be used as conduits, filters, switches, reaction chambers, etc.

1 / 5 (1) Sep 16, 2011
sounds interesting, but the article provides no actual numbers, so who can tell?
Physorg, your service should be to provide information to us more easily than we can get it ourselves. You do this by having a journalist read the paper and talk to the researched, this information is then distilled into an article and presented to us. The efficiency is gained in that the journalist only needs to do this once, whereas each of us would need to do it independently. Also many of us simply dont have the time or expertise to be able to wade through the papers and research, thats your job.
You are failing to provide the actual information, you are just copy/pasting a press release, this is not your job.
not rated yet Sep 17, 2011
7.3% conversion efficiency according to the paper... Not exactly what I'd call amazingly high but good for polymer PV I suppose.
not rated yet Sep 17, 2011
7.3% is double the efficiency of the solar cells you see on top of those accent lights that adorn gardens, and slightly higher than the photosynthetic efficiency of photosynthesis.

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