Researchers at University of Tsukuba and National Institute for Materials Science use charge formation efficiency to screen materials for future devices
Organic photovoltaic cells -- a type of solar cell that uses polymeric materials to capture sunlight -- show tremendous promise as energy conversion devices, thanks to key attributes such as flexibility and low-cost production.
Yutaka Moritomo/University of Tsukuba
Researchers develop method to screen organic materials for organic photovoltaic cells by charge formation efficiency.
But one giant hurdle holding back organic photovoltaic technologies have been the complexity of their power conversion processes, which involve separate charge formation and transport processes.
To maneuver around this problem, a team of researchers in Japan has developed a method to determine the absolute value of the charge formation efficiency. The secret of their method, as they report in Applied Physics Letters, is the combination of two types of spectroscopy.
The two types the team uses are photo-induced spectroscopy to determine the change in absorption after femtosecond photo-pulse excitation, and electrochemical spectroscopy to examine the absorption change due to charge injection.
"By qualitative analysis of the spectral change, we can deduce how many charges are produced by one photon -- its charge formation efficiency," said Professor Yutaka Moritomo, Institute of Materials Science at the University of Tsukuba.
Just how significant is this? It's a huge step forward, said Moritomo, and the team also discovered that the charge formation efficiency remains high (0.55) even at low temperatures (80 K).
"This was extremely surprising," Moritomo said, since the positive and negative charges are strongly bound in an organic photovoltaic device as an exciton -- a bound state of an electron and hole, which are attracted to each other by the electrostatic Coulomb force.
"Its charge formation was believed to be too difficult without a thermal activation process," explained Moritomo. "But our work shows that the charge formation process of an organic photovoltaic device is purely quantum mechanical, and any theoretical model should explain the high charge formation efficiency at low temperatures."
The team's work will enable the high-throughput screening of organic materials for new organic photovoltaic devices. "Organic materials have several requirements -- including high charge formation efficiency and high charge transport efficiency -- so our method can be used to quickly screen the materials by charge formation efficiency," Moritomo said.
Next for the team? "Now that we have a method to determine the key physical parameter, charge formation efficiency, we're exploring the interrelation between it and the nanoscale structure of the organic photovoltaic device to clarify the mechanism of the charge formation," noted Moritomo.
The article, "Effect of temperature on carrier formation efficiency in organic photovoltaic cells," is authored by Yutaka Moritomo, Kouhei Yonezawa and Takeshi Yasuda. It will appear in the journal Applied Physics Letters on August 19, 2014. After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/105/7/10.1063/1.4892611
ABOUT THE JOURNAL
Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See: http://apl.aip.org
Jason Socrates Bardi | newswise
Glass's off-kilter harmonies
18.01.2017 | University of Texas at Austin, Texas Advanced Computing Center
Explaining how 2-D materials break at the atomic level
18.01.2017 | Institute for Basic Science
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
19.01.2017 | Earth Sciences
19.01.2017 | Life Sciences
19.01.2017 | Physics and Astronomy