Skip to comments.Organic Crystal Allows Excitons to Travel Further, Produces More Efficient Plastic Solar Cells
Posted on 10/12/2010 10:33:05 AM PDT by Ernest_at_the_Beach
Rubrene crystal raises hope for the use of organic semiconductors and cheaper, more efficient solar cells
Rutgers University physicists have found new properties within a material that could lead to the production of less expensive and more efficient plastic solar cells.
Vitaly Podzorov, co-author of the study and assistant professor of physics at Rutgers University, along with his research team have discovered that organic semiconductors allow energy-carrying particles -- which are created by "packets" of light -- to journey a thousand times farther than researchers previously thought.
"Organic semiconductors are promising for solar cells and other uses, such as video displays, because they can be fabricated in large plastic sheets," said Podzorov. "But their limited photovoltaic conversion efficiency has held them back. We expect our discovery to stimulate further development and progress.
Podzorov and his team came to these conclusions by observing excitons, which are particles that consist of an electron and an electron hole where a positive charge is attributed to the absence of an electron. Excitons form when semiconducting materials absorb photons, which are light particles.
The problem with organic semiconductors up until this point was that they were observed to travel less than 20 nanometers. This is an issue because electrons and the holes move to the two opposite sides when they "hit" a semiconductor junction or boundary. If these excitons only diffuse "tens of nanometers," the only ones that generate photo-voltage are those closest to the boundaries or junctions.
"Now we lose 99 percent of sunlight," said Podzorov.
But now, Podzorov and his team have observed that excitons can journey a thousand times farther than previously thought in rubrene, which is an extremely pure crystal organic semiconductor.
"This is the first time we observed excitons migrating a few microns," said Podzorov. "Once the exciton diffusion distance becomes comparable to the light absorption length, you can collect most of the sunlight for energy conversion."
Excitons within the rubrene crystal acted like excitons in inorganic crystals, which means better opto-electronic properties, increased efficiency and lower costs. Podzorov and his team hope, with further development, that solar cells based on this technology can replace silicon solar cells.
In the midst of this research Podzorov also discovered a new way of measuring excitons based on optical spectroscopy. Excitons are hard to measure because they are not charged, so the Rutgers University research team created a new method called polarization resolved photocurrent spectroscopy, which "dissociates" excitons at the surface of the crystal and exposes large photocurrent.
This study will be in an upcoming issue of Nature Materials, where Podzorov has submitted other relevant and recent research on organic semiconductors.
but will they power a warp engine?
bump for later
Rubrene (5,6,11,12-tetraphenylnaphthacene) is a red colored polycyclic aromatic hydrocarbon. Rubrene is used as a sensitiser in chemoluminescence and as a yellow light source in lightsticks.
As an organic semiconductor, the major application of rubrene is in organic light-emitting diodes (OLEDs) and organic field-effect transistors, which are the core elements of flexible displays.
And a picture:
Packing of rubrene molecules (Carbon atoms in the tertacene backbone are coloured yellow for clarity).
Are these the same as Dilithiam Crystals?
It would be great if we could reach the point where each home produces its own power, especially as a defense against potential terrorist attacks on the electrical grid, but so far the economics just aren't there. All of the larger solar power projects across the country that are being touted by liberals are just for show. None of them make sense economically.
Interesting article. I have never had organic chemistry, but have had more than my share of advanced mineralogy, which is basically the chemistry of silicates. This article brings back a lot of memories of the complexity of the subject.
So if there is more conductivity with the oxygen defect does it’s presence lessen the initial capturing of photons by a more pure form of the rubrene?
Now whatcha gonna do?
Forgive the format of my post and any spelling or grammatical errors, first post I have done via my cell phone