Name: effect of bending on the electrical characteristics of flexible organic single crystal-based field-effect transistors
Uploaded: 2016-11-07T14:00:00
Description: Watch this Scientific Journal Video about Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors at JoVE.com

This work was supported by the Ministry of Science and Technology, Taiwan, Republic of China through Grant No. 101-2113-M-001-006-MY3.

1. Preparation of TCDAP12
<ol>
	<li>Synthesize TCDAP by following literature procedures13.</li>
	<li>Purify the TCDAP product by the temperature-gradient sublimation method, with the three temperature zones set at 340, 270, and 250 &#176;C, respectively, under a vacuum pressure of 10-6 Torr12,14.</li>
</ol>
2. Grow Single Crystals of TCDAP Using a Physical Vapor Transfer (PVT) System14
<ol>
	<li>Put the TCDAP sample at one end of a boat (5...

<ol>
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In this experiment, a number of parameters affect the successful measurement of the field-effect mobility. Firstly, the single crystal should be large enough to be fabricated into a field-effect device for property measurement. The physical vapor transfer (PVT) method is the one that allows larger crystals to be grown. By adjusting the temperature and the flow rate of the carrier gas, crystals of sizes up to half a centimeter can be obtained. Secondly, the choice of a single crystal is important. An apparent single cryst...

Soft electronic devices, such as sensors, displays, and wearable electronics, are currently being designed and researched more actively, and many have even been launched in the market in recent years1,2,3,4. Organic semiconducting materials play an important role in these electronic devices due to their inherent advantages, including low development cost, the ability to be prepared in solution or at low temperatures, and, in particular, their flexibility when compared to inorganic semiconductors5,6. One special consideration for these electronics is that they will be subjected to frequent bending. Bending introduces strain in the components and the materials within the device. A stable and consistent performance is required as such devices are bent. Transistors are a vital component in most of these electronics, and their performance under bending is of interest. A number of studies have addressed this performance issue by bending organic thin film transistors7,8. While the changes in conductance upon bending may be attributed to the changes in spacing between the grains in a polycrystalline thin film, a more fundamental question to ask is whether the conductance may change within a single crystal upon bending. It is well accepted that charge transport between organic molecules depends strongly on electronic coupling between molecules and the reorganization energy involved in the interconversion between the neutral and charged states9. Electronic coupling is highly sensitive to the distance between neighboring molecules and to the overlap of frontier molecular orbitals. The bending of a well-ordered crystal introduces strain and may change the relative position of molecules within the crystal. This can be tested with a single crystal-based field-effect transistor. One report used single crystals of rubrene on a flexible substrate to study the effect of crystal thickness upon bending10. Devices with copper phthalocyanine nanowire crystals prepared on a flat substrate were shown to have a higher mobility upon bending11. However, the properties for an FET device bent in different directions have not been explored.
The molecule 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) is an n-type semiconductor material12. The crystal of TCDAP has a monoclinic packing motif with shifted&#160;&#960;-&#960; stacking between neighboring molecules along the a axis of the unit cell at a cell length of 3.911 &#197;. The crystal grows along this packing direction to give long needles. The maximum n-type field-effect mobility measured along this direction reached 3.39 cm2/V&#183;sec. Unlike many organic crystals that are brittle and fragile, TCDAP crystal is found to be highly flexible. In this work, we used TCDAP as the conducting channel and prepared the single crystal field-effect transistor on a flexible substrate of polyethylene terephthalate (PET). Mobility was measured for the crystal on a flat substrate, with the device bent toward the flexible substrate (downward) or bent toward the gate/dielectric side (upward). I-V data were analyzed based on changes in the stacking/coupling distance among the neighboring molecules.

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effect of bending on the electrical characteristics of flexible organic single crystal-based field-effect transistors

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling immensely. However, in soft electronics, in which organic semiconductors play a critical role, the devices will be bent or folded repeatedly. The effect of bending on the crystal packing and thus the charge transport is crucial to the performance of the device. In this manuscript, we describe the protocol to bend a single crystal of 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) in the field-effect transistor configuration and to obtain reproducible I-V characteristics upon bending the crystal. The results show that bending a field-effect transistor prepared on a flexible substrate results in nearly reversible yet opposite trends in charge mobility, depending on the bending direction. The mobility increases when the device is bent toward the top gate/dielectric layer (upward, compressive state) and decreases when bent toward the crystal/substrate side (downward, tensile state). The effect of bending curvature was also observed, with greater mobility change resulting from higher bending curvature. It is suggested that the intermolecular &#960;-&#960; distance changes upon bending, thereby influencing the electronic coupling and the subsequent carrier transport ability.

The single crystal XRD analysis reveals that TCDAP is an extended &#960; system with molecules packing along the a axis. Fig. 2 shows the scan pattern by powder XRD for a TCDAP crystal. A series of sharp peaks are observed, corresponding only to the family of (0,k,&#8467;) planes, by comparing with the powder diffraction pattern of the crystal. This would imply that the crystal structure is oriented as shown in Fig. 3.
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Watch this Scientific Journal Video about Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors at JoVE.com

Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors

This manuscript describes the bending process of an organic single crystal-based field-effect transistor to maintain a functioning device for electronic property measurement. The results suggest that bending causes changes in the molecular spacing in the crystal and thus in the charge hopping rate, which is important in flexible electronics.

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling ...

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