Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications1,2,3,4,5. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice6. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π–π stacking distance) greatly influences electron orbital overlap and therefore mobility7. Using our method to incrementally introduce lattice strain, we alter the π–π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33 Å to 3.08 Å. We believe that 3.08 Å is the shortest π–π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π–π distance of 3.04 Å has been achieved through intramolecular bonding8,9,10). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from 0.8 cm2 V−1 s−1 for unstrained films to a high mobility of 4.6 cm2 V−1 s−1 for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.
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We thank A. Salleo, J. E. Anthony, H. Li, A. Sokolov and J. Rivnay for discussions. We thank J. E. Anthony and M. M. Nelson of 3M Corp. for providing high-purity TIPS-pentacene. This publication was partially supported by the National Science Foundation DMR-Solid State Chemistry (DMR-0705687-002), the Samsung Advanced Institute of Technology, the Global Climate and Energy Project at Stanford University (SPO 25591130-45282-A) and the Air Force Office of Scientific Research (award number FA9550-09--0256). E.V. thanks the Eastman Kodak Corporation Kodak Fellows Program for support. Z.B. acknowledges support from the David Filo and Jerry Yang Faculty Fellowship from Stanford University. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of Stanford University, the Sponsors of the Global Climate and Energy Project, or others involved with the Global Climate and Energy Project.
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High-resolution patterning of solution-processable materials via externally engineered pinning of capillary bridges
Nature Communications (2018)