Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Organic Solar Cells More Efficient With Molecules Face-to-Face

07.04.2014

New research from North Carolina State University and UNC-Chapel Hill reveals that energy is transferred more efficiently inside of complex, three-dimensional organic solar cells when the donor molecules align face-on, rather than edge-on, relative to the acceptor. This finding may aid in the design and manufacture of more efficient and economically viable organic solar cell technology.

Organic solar cell efficiency depends upon the ease with which an exciton – the energy particle created when light is absorbed by the material – can find the interface 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.


Molecules in face-on orientation inside organic solar cell. Artist: Peter Allen

While this sounds straightforward enough, the reality is that molecules within the donor and acceptor layers can mix, cluster into domains, or both, leading to variances in domain purity and size which can affect the power conversion process. Moreover, the donor and acceptor molecules have different shapes, and the way they are oriented relative to one another matters. This complexity makes it very difficult to measure the important characteristics of their structure.

NC State physicist Harald Ade, UNC-Chapel Hill chemist Wei You and collaborators from both institutions studied the molecular 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 orientation 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 alignment 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 inhibit recombination, or charge loss, in organic solar cells,” Ade says, “though precisely 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, like fettucine, as the donor polymer, and then add ‘ground meat,’ or a round acceptor molecule, 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 randomly 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.”

The paper appears online April 6 in Nature Photonics. Fellow NC State collaborators were John Tumbleston, Brian Collins, Eliot Gann, and Wei Ma. Liqiang Yang and Andrew Stuart from UNC-Chapel Hill also contributed to the work. The work was funded by the U.S. Department of Energy, Office of Science, Basic Energy Science, the Office of Naval Research, and the National Science Foundation.

-peake-

 Note to editors: Abstract of the paper follows.

“The influence of molecular orientation on organic bulk heterojunction solar cells”

Authors: John R. Tumbleston, Brian A. Collins, Eliot Gann, Wei Ma and Harald Ade, North Carolina State University; Liqiang Yang, Andrew C. Stuart and Wei You, University of North Carolina at Chapel Hill

Published: April 6, 2014, in Nature Photonics

Abstract:

In bulk heterojunction organic photovoltaics, electron-donating and electron-accepting materials form a distributed network of heterointerfaces in the photoactive layer, where critical photo-physical processes occur. However, little is known about the structural properties of these interfaces due to their complex three-dimensional arrangement and the lack of techniques to measure local order. Here, we report that molecular orientation relative to donor/acceptor heterojunctions is an important parameter in realizing high-performance fullerene-based, bulk heterojunction solar cells. Using resonant soft X-ray scattering, we characterize the degree of molecular orientation, an order parameter that describes face-on (+1) or edge-on (-1) orientations relative to these heterointerfaces. By manipulating the degree of molecular orientation through the choice of molecular chemistry and the characteristics of the processing solvent, we are able to show the importance of this structural parameter on the performance of bulk heterojunction organic photovoltaic devices featuring the electron-donating polymers PNDT–DTBT, PBnDT–DTBT or PBnDT–TAZ.

Tracey Peake | EurekAlert!
Further information:
http://news.ncsu.edu/releases/tp-adephotonics/

Further reports about: Cells Collins Efficient Energy Molecules Organic Photonics Picture X-ray complexity processing

More articles from Power and Electrical Engineering:

nachricht IHP presents the fastest silicon-based transistor in the world
05.12.2016 | IHP - Leibniz-Institut für innovative Mikroelektronik

nachricht High-precision magnetic field sensing
05.12.2016 | ETH Zurich

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

IHP presents the fastest silicon-based transistor in the world

05.12.2016 | Power and Electrical Engineering

InLight study: insights into chemical processes using light

05.12.2016 | Materials Sciences

High-precision magnetic field sensing

05.12.2016 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>