Research carried out by scientists from the School of Chemistry and Biochemistry, with the Centre for Organic Photonics and Electronics at the Georgia Institute of Technology, is leading to a theoretical framework that can improve dramatically the performance of devices based on what is known as "Plastic Electronics", among which are found as leading to OLED displays and certain types of organic solar cells. The paper talks about a method used to eliminate "energy traps" which falls a percentage of electrons, while the current flows within these polymer semiconductors. Find out all the details of the find in this article.
During his tenure in semiconductors, while giving rise to the phenomenon we know as "current flow", there is a proportion of electrons that are "stuck" in certain load traps are no longer useful, lowering the efficiency of OLED devices , for example. "This process reduces electron capture the circulating current (appears as a resistor) and generally, this type of energy traps are moved toward the center of the device, where the electrons are converted into photons or vice versa, for the For solar cells, "the team from the University of Groningen and the Georgia Institute of Technology. Although several mechanisms, or simulation models have been proposed to explain the workings and nature of such traps, until now, no one knew for sure how it occurred, its nature, nor how it could build an antagonistic mechanism, capable of neutralizing its negative effect in normal operation of a traditional semiconductor element.
"We set out to solve this puzzle by comparing the properties they acquired these traps in nine different types of polymers. The comparison showed that the traps in all materials, had a similar energy level," said Herman Nicolai , author of a paper on the subject in Nature Materials ("Unification of trap-limited electron transport in semiconducting polymers"). As part of development work, the Georgia Tech group, led by Jean-Luc Bredas, used as models to study the electronic structures in a wide range of possible pitfalls. "What we found out of the calculation is that the energy level of traps, measured experimentally, coincided with the effects that might induce a complex (or combination) of water and oxygen.
"Although the devices were fabricated Nicolai studied in an atmosphere of nitrogen "these" impurities "(water-oxygen), can easily be introduced during manufacture of semiconductor material, even if the process is done under controlled conditions. Nitrogen can not prevent the contamination with small amounts of oxygen and water. " According to these results, the traps that are now known to effectively thanks to these studies, have a similar energy level, therefore the flow of electrons in different plastic materials can be estimated more easily, and opens a possibility stronger to support the design and building materials free of traps.
"The energy of the trap is in the forbidden energy gap," said Nicolai. This interval is the gap (space) representing the energy difference of the outside of the circle in which electrons orbit the nucleus in its ground state, higher orbit and why they should move (or move) to become mobile charge carriers (those forming the electron current). For example, when a moving electron flows in the vicinity of the area inhabited by a "trick" that is mentioned in the energy space, fall into this trap because it has a lower energy level. "From this research, if the chemicals could (or could) design semiconducting polymers where the energy of the traps is greater than that of the superior orbital in which electrons move through the material, they would not fall into the traps reaching the effectiveness of a material far superior to those of today. "said Nicolai.
In both devices, LEDs, plastic and plastic solar cells, "The flow of electrons should not be hampered by power outages. From now on, with our discovery, the designs can be made with more efficient results." The experimental work was conducted at the Institute for Advanced Materials Zernike (ZIAM) in the Faculty of Mathematics and Natural Sciences, University of Groningen in the Netherlands.
