Understanding and tuning organic semiconductor packing during solution processing
- Circuits based on organic semiconductors (OSCs) are being currently explored for flexible, transparent and low-cost electronic applications. However, to realize such applications, the charge transport performance of OSCs in thin film transistors (TFTs) must be improved. Using a solution processing method called solution shearing, we were able to create metastable polymorphs of various OSCs and improve the electronic performance. This is the first time industrially friendly coating processes have been utilized to change the molecular packing of OSCs. Changing the molecular packing to form metastable polymorphs through solution processing allows researchers to complement traditional synthetic methods to generate high performance OSCs. The first part of my research work details the use of solution shearing to increase the mobility of small molecular OSCs. The model OSC 6,13-bis(triisopropylsilylethynyl) pentacene (TPn) is used as the model compound for our study, and various metastable polymorph are created through solution processing. The highest mobility obtained for the metastable TFTs (4.6 cm2 V-1 s-1 ) is three times higher than the previous highest mobility found in literature. The lattice strain method to modify OSC charge transport was shown to be general to certain classes of small molecule and polymeric OSCs as well. In order to study crystallization of OSCs during solution shearing, my research extended to constructing a miniaturized solution shearing machine to be used in-situ at synchrotron facilities. We obtained high speed (100 frames/s), in-situ images of metastable crystal growth using a microbeam (20 [micrometer]) grazing incidence X-ray diffraction (GIXD) method. Using knowledge from these experiments, we were able to obtain design rules for creating lattice strain and polymorphism using other solution processing techniques. Finally, our research has brought the use of lattice strain closer industrial use through the use of selective deposition of OSCs. Industrial applications of lattice strained OFETs requires that the OFETS are patterned. We have developed a surface functionalization procedure that utilizes hydrophobic/hydrophilic interactions to isolate lattice strained OSCs. We show that charge carrier mobilities over 2 cm2/Vs are possible in the patterned OFETs of TIPS-pentacene, and that strained OFETs can exist at patterning sizes of 100 microns and lower. We show that the pattern size can have an effect on the lattice strain possible in the OSCs, and investigate methods that enable sub 10 micron scale patterning using solution shearing. In summary, we have shown that high performance, metastable polymorphs of various organic semiconductors can be fabricated through solution processing methods, and the underlying reasons for polymorphism is explained through the use of in-situ X-ray diffraction techniques.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Chemical Engineering.
|Fuller, Gerald G
|Fuller, Gerald G
|Statement of responsibility
|Submitted to the Department of Chemical Engineering.
|Thesis (Ph.D.)--Stanford University, 2013.
- © 2013 by Gaurav Giri
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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