A study, carried out by an international team of researchers led by Vitaly Podzorov at Rutgers University-New Brunswick, has revealed that the efficiency of semiconductors made of organic materials can be doubled by bending them slightly. The results of the research, published this November in the Journal Advanced Science, will influence the development of next-generation electronics like solar cells, sensors, and wearables.
Enhancing Organic Semiconductor Efficiency to Benefit the Future of Electronics
Improving the electrical flow of organic semiconductors has the potential to revolutionize the technology of tomorrow and, for this reason, it has become a major focus of a scientific investigation.
Organic electronics are seen as the future of technology; they have the potential to offer cheaper semiconductors and the prospect of developing more ecological devices that have enhanced properties, such as better energy recovery, flexible displays, and flexible lighting. They have also already been used to develop printed solar cells, giving them the potential to disrupt the renewable energy sector, helping to make renewables cheaper and more efficient.
A semiconductor is essentially a material that conducts electricity but is also tunable to different inputs. Organic semiconductors are defined by their construction out of organic molecules, which is usually a combination of carbon and hydrogen atoms.
The molecules are arranged in structures of light, flexible van der Waals molecular crystals that can harness light, making them vital to the development of optoelectronics. The alternative, traditional silicon and germanium semiconductors will likely eventually be replaced by organic semiconductors, due to their drawbacks of being expensive and inflexible, limiting their applications.
However, before organic semiconductors can take over space, more research needs to be conducted to allow scientists to harness their full potential. Currently, organic semiconductors are not efficient enough for the applications that they are planned to be used in.
Earlier this year a vital breakthrough was made in this area, leading to double doped primers, that could double the efficiency of organic electronics. The study from researchers at Chalmers University of Technology, Sweden, demonstrated the true untapped potential of organic semiconductors, inspiring other international teams to continue development.
The Rutgers team aimed to enhance the efficiency of organic semiconductors further. They noted that while organic semiconductors can now allow electricity to flow through at ten times the speed of inorganic silicon semiconductors, the potential to increase this flow has still not been fully realized. Strain engineering is the process of tuning semiconductors by bending them; a technique that had not, until this point, been investigated in studies that yielded conclusive results. This is what the Rutgers team set out to achieve.
The Research
Researchers planned to obtain evidence on the effect of bending on the efficiency of electricity conduction. The study was designed to explore the intrinsic effects of strain applied to the trap‐free charge carrier mobility. The method of applying uniaxial mechanical strain to the flexible single‐crystal transistors was decided to be the most convenient approach to observing these intrinsic effects.
The team noted that while there have been strain variable measurements in single‐crystal organic semiconductors, the effects of the Hall effect versus strain in organic semiconductors had not been investigated. They recognized that studying this would uncover the response of the intrinsic (trap-free) carrier mobility to strain. The team quantified the strain effect on mobility by a strain factor, developing an equation to efficiently measure the impact of strain on electrical flow.
To address potential ambiguity in results, the team coupled four‐probe FET measurements of ultrathin single‐crystal organic transistors subjected to a calibrated uniaxial strain along with their Hall effect studies.
The Results
The data from the Raman measurements demonstrated that under compressive (tensile) strain the low‐frequency molecular vibrations hardened, this effect was found to correspond with certain Raman modes that were consistent with the changes observed in the charge carrier mobility with strain. This is the first time that these results have been produced from an experimental study. The team was able to calculate that bending the organic transistor by just 1% could double the speed of the flow of electrons.
Future Developments
What the team achieved will be vitally important to the future of electronics. The knowledge attained will inform the development of organic semiconductors, which will shape the potential functions of future electronic devices, including those that will have a significant impact on human life, such as solar cells and wearables.
Sources and Further Reading
- Choi, H., Yi, H., Tsurumi, J., Kim, J., Briseno, A., Watanabe, S., Takeya, J., Cho, K. and Podzorov, V. (2019). A Large Anisotropic Enhancement of the Charge Carrier Mobility of Flexible Organic Transistors with Strain: A Hall Effect and Raman Study. Advanced Science, p.1901824. https://onlinelibrary.wiley.com/doi/full/10.1002/advs.201901824
- Kiefer, D., Kroon, R., Hofmann, A., Sun, H., Liu, X., Giovannitti, A., Stegerer, D., Cano, A., Hynynen, J., Yu, L., Zhang, Y., Nai, D., Harrelson, T., Sommer, M., Moulé, A., Kemerink, M., Marder, S., McCulloch, I., Fahlman, M., Fabiano, S. and Müller, C. (2019). Double doping of conjugated polymers with monomer molecular dopants. Nature Materials, 18(2), pp.149-155. https://www.nature.com/articles/s41563-018-0263-6
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