new research from north carolina state university and unc-chapel hill reveals that energy is transferred more
1 inside of complex, three-dimensional organic solar cells when the
2 4 5 face-on, rather than edge-on, relative to the acceptor. this finding may aid in the design and manufacture of more efficient and economically
6 organic solar cell technology. organic solar cell efficiency depends upon the ease with which an
exciton（激子） -- the energy particle created when light is absorbed by the material -- can find the
7 between the donor and acceptor molecules within the cell. at the interface, the exciton is converted into charges that travel to the electrodes, creating power. while this sounds
8 enough, the reality is that molecules within the donor and acceptor layers can mix, cluster into
10, or both, leading to
11 in
9 purity and size which can affect the power
12 process. moreover, the donor and acceptor molecules have different shapes, and the way they are oriented relative to one another matters. this
13 makes it very difficult to measure the important characteristics of their structure.
nc state
14 harald ade, unc-chapel hill chemist wei you and collaborators from both institutions studied the
15 composition of solar cells in order to determine what aspects of the structures have the most impact on efficiency. in this project the team used advanced soft x-ray techniques to describe the
16 of molecules within the donor and acceptor materials. by manipulating this orientation in different solar cell polymers, they were able to show that a face-on
17 between donor and acceptor was much more efficient in generating power than an edge-on alignment.
"a face-on orientation is thought to allow favorable interactions for charge transfer and
18 recombination, or charge loss, in organic solar cells," ade says, "though
19 what happens on the molecular level is still unclear.
"donor and acceptor layers don't just lie flat against each other," ade explains. "there's a lot of mixing going on at the molecular level. picture a bowl of flat
pasta（面团）, like
fettucine（宽面）, as the donor polymer, and then add 'ground meat,' or a round acceptor
3, and stir it all together. that's your solar cell. what we want to measure, and what matters in terms of efficiency, is whether the flat part of the fettuccine hugs the round pieces of meat -- a face-on orientation -- or if the fettuccine is more
20 oriented, or worst case, only the narrow edges of stacked up pasta touch the meat in an edge-on orientation. it's a complicated problem.
"this research gives us a method for measuring this molecular orientation, and will allow us to find out what the effects of orientation are and how orientation can be fine-tuned or controlled."
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