Polymers are the material of choice for making thin-film transistors and solar cells. They are also potentially suitable for manufacture using economical, high-throughput techniques, such as roll-to-roll and inkjet printing processes. However, transistors and solar cells have traditionally used different kinds of polymers, and this can severely complicate the fabrication process. Zhi-Kuan Chen at the A*STAR Institute of Materials Research and Engineering and co-workers have now developed a versatile polymer that is suitable for both kinds of devices.
Polymers with high-charge mobilities are ideal to use in the manufacture of transistors. However, these materials are susceptible to having large energy bandgaps, which prevent them from absorbing portions of the solar spectrum. Such materials could severely hamper the energy conversion efficiency if made into solar cells.
The researchers focused on a class of polymers called polythiophenes, derivatives of which have been measured to have high hole (or positive charge) mobilities. However, polythiophenes also have a large energy bandgap, which prevents them from absorbing light with red-orange wavelengths longer than 650 nm, thus reducing solar cell performance.
Previous work by other researchers has shown that this bandgap can be lowered by making modifications to the backbone of the polythiophene chain with groups of atoms that are able to accept charge. Even so, the power conversion efficiency of the resulting solar cells was below 2.3%, less than half of the best-performing polymer cells.
Chen and co-workers followed in the steps of their predecessors by modifying a polythiophene polymer. The result was a novel polymer called POD2T-DTBT that was measured to have a relatively low bandgap which resulted in an optical absorption range that extended to red-orange wavelengths of 780 nm, thus taking in more of the solar spectrum. At the same time, the hole mobility of the polymer was measured to be 0.20 cm2 per volt per second, comparable to unmodified polythiophene. This allowed for fabrication of high-performance transistors and solar cells. In particular, by combining POD2T-DTBT with the ester PC71BM, the research team constructed a solar cell with a power conversion efficiency of 6.26%, comparable to the efficiency of the best polymer cells to date.
This strong performance was drawn in part from the morphology of the thin films that resulted from the POD2T-DTBT / PC71BM mixture. Electron microscopy of the films showed that the two components were intimately mixed together: the long white fibers, which are 20–25 nm in width, correspond to the polymer, and the darker domains correspond to the ester (see image). The high-charge mobility of the POD2T-DTBT polymer itself also boosted performance.
Ong, K.-H. et al. A versatile low bandgap polymer for air-stable, high-mobility field-effect transistors and efficient polymer solar cells. Advanced Materials 23, 1409–1413 (2011).
Physics, photosynthesis and solar cells
01.12.2016 | University of California - Riverside
New process produces hydrogen at much lower temperature
01.12.2016 | Waseda University
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...
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...
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,...
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...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy