According to Science Daily, organic semiconductors have won awards for light emitting diodes (LEDs), field effect transistors (FETs), and photovoltaic cells. Because they can be printed by solution, they provide highly scalable, cost-effective, silicon-based devices. alternative plan. However, the uneven performance of organic semiconductors has always been a problem. Scientists know that the performance problem stems from the interface inside the organic semiconductor film, but it has been unclear why, and this puzzle was not solved until recently.
Mixed randomly arranged nanocrystallites, which are sieged by dynamics during solution casting
Scientists at the US Department of Energy (DOE) Lawrence Berkeley National Laboratory and Naomi Ginsberg of the University of California, Berkeley, led a team of scientists who studied the name of a unique form of microscopy. TIPS-pentacene is a special high-performance organic semiconductor interface. She and her team discovered a mix of randomly arranged nanocrystallites that are sieged by dynamics when the solution is cast. Like wrecks on the highway, these nanocrystallites impede the flow of charge carriers.
"If the interfaces are clean and tidy, they won't have a huge impact on performance, but the presence of nanocrystallites reduces the mobility of charge carriers," said Ginsberg. "Our nanocrystallite model built on this interface - which is consistent with observations - provides crucial information that can be used to relate the method of treating the solvent to the optimal equipment performance."
Kingsberg, of the Law Department of Physical and Biological Sciences and Materials Science at the Lawrence Berkeley National Laboratory and the University of California, Berkeley, is the author of the article published in the journal Nature Communications. Other authors of the article include Cathy Wong, Benjamin Cotts, and Hao Wu.
Organic semiconductors are based on the ability of carbon to form larger molecules, such as benzene rings and pentacene, which have electrical conductivity between the insulator and the metal. Through solution processing, organic materials can be molded into crystalline films without the need for expensive high-temperature heat treatment—these are the processes that silicon and other non-organic semiconductors must go through. However, even though it is well known that the crystal interface in a semiconductor organic film is critical to the performance of the device, the morphological information about these interfaces prior to this study is still unknown.
“Semiconductor thin-film interfaces are smaller than the diffraction limit. Surface detection techniques, such as atomic force microscopy, cannot detect it. In addition, the use of X-ray methods generally cannot solve its nano-heterogeneity,†explains Ginsberg. "In addition, the crystal TIPS-pentacene we studied was almost zero, which means that it cannot be studied with photoluminescence microscopy."
Ginsberg and her team overcome this problem by using transient absorption spectroscopy (TA) microscopy, which uses femtosecond laser pulses to activate transient energy states so that the detector can measure absorption spectra. change. The team conducted transient absorption spectroscopy on their own optical microscope, which allowed them to produce a thousand times smaller focal volume than traditional TA microscopy. They also deployed different polarizations of light so that they could isolate the interface signals that could not be observed in the vicinity.
"Instruments and equipment, including very good detectors, combined with tireless data collection ensure a good signal-to-noise ratio, and our method of changing experiments and analysis is crucial to the success we have achieved," Ginsberg explained. "Our spatial resolution and light polarization sensitivity are also very important for clearly observing interface signals." The method proposed by Ginsberg and her team to uncover the structural patterns in the hidden interface of organic semiconductor thin films will become scalable and Bear the new predictors of these materials. This predictive power will help reduce discontinuities and maximize charge carrier mobility. Currently, researchers use a trial and error method to test the performance of the resulting equipment by testing different solution casting environments.
"Our method provides important media in the device's optimized feedback loop, primarily by defining the microscopic details of the membrane that enters the device, and at the same time inferring what structure the solution casting will produce at the interface." Kingsberg This is indicated. "The result is that we know how to change the delicate balance between solution casting parameters to produce a more functional film."
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