Heterocyclic Organic Compounds Arranged - Case Study Example

Poly (3-hexylthiophene) (P3HT) By Candi s (This page intentionally left blank) Thiophene, of which Poly (3-hexylthiophene) (P3HT) is aderivative, present heterocyclic organic compounds arranged in a ring structure with the inclusion of a sulphur atom (Lancaster, 2010, Section 2.6) and (Nalwa, 2001, Pp. 12 – 15). Tar, gas, and industrial benzene obtained from coal contain Thiophene, whose molecular structure is in the figure below and there are numerous derivatives of Thiophene that are of current interest. According to (Nalwa, 2001, Pp. 12 – 15), existing literature on polythiophenes is extensive, with new publications appearing every day, but Poly (3-hexylthiophene) (P3HT) conjugated polymers, of which P3HT is a kind, are one of the most promising candidates for the active layer of low-cost Organic-field-effect transistors (OFETs) and organic thin film transistors (TFTs) (Joshi, 2008, Chapter 1). Polythiophene is of interest because although manufacturing of high performance TFTs from vapour phase deposition is possible, conducting polymers, including P3HT, lend themselves to processing in solution that reduces the manufacturing cost of the OTFTs (Park, 2007, Chapter 2). Materials capable of processing in solution are attractive because it is possible to manufacture films exhibiting good characteristics simply by spin coating, casting or printing at low temperatures (Singh, 2008, Pp. 158 – 159). According to Lancaster (2010, Pp. 73 – 75), the most efficient configuration of P3HT for electrical conduction is the head to tail coupling of alkyl chains presented in Figure 2, below and this means that this configuration is of the greatest interest to those interested in the fabrication of TFTs. The previously mentioned author and Skotheim (2007, Chapter 1) goes further to state that the head to tail structure of P3HT encourages a low energy planer state for carbon backbone to reduce Ω bond overlaps and the minimisation of the static hindrance between hexyl side chains to present the highest charge mobility for P3HT. Table 1, below, presents the recorded highest field effect mobility values for OTFTs presented in published literature from 1986 to 2005. Figure 1: Structure of Polythiophene, from (Nalwa, 2001, Pp. 12) Figure 2: Molecular Structure for Regio Regular P3HT, from (Lancaster, 2010, Pp. 74) Table 1: Highest Field Effect Mobility Values reported in Published Literature from 1986 to 2005, for OTFTs, from (Singh, 2008, Pp. 157) Singh (2008, Pp. 158 – 159) states that the addition of alkyl side chains in Polythiophenes improves the solubility of polymer chains, even though the side chains are insulating, and their addition presents mobility comparable to regular P3HT. However, longer side chains decreases mobility. The ionization potential of P3HT presents ionisation potential of 4.9 – 5 eV, best suited to form ohmic contacts with many air-stable electrode materials for TFTs, including Au. Pure polythiophene without the side chains is neither soluble nor fusible and this means that this is not useful for making OTFTs (Joshi, 2008, Pp. 11). The previously mentioned author goes further to state that the regio regularity of P3HT, the processing methods and conditions, treatment of the gate dielectric / gate insulator and solvents used for processing of P3HT together with annealing, molecular weights affect the packaging structure of P3HT, and the type of OTFTs produced. In addition, P3HT is more readily made, and this material is, therefore, more available. However, P3HT still presents lower manufacturing process costs and retains a strong interest for fabrication of OTFTs, despite the fact that polymers with better performance in terms of charge carrier availability are now available (Fumagalli, 2008, Pp. 104 – 105). According to Skotheim (2007, Pp. 207), a need exists for carefully designing the process of film deposition for fabrication of the OTFT and P3HT) shows much higher hole mobilities than regio random polymers and values up to 0.10–0.30 cm2 V_1 s_1 have been claimed. Apart from the promise that P3HT shows for OTFT fabrication, this material is also suitable for fabrication of arrays of OTFTs on flexible substrates, such as for Organic Light Emitting Diode (OLED) displays (Skotheim, 2007, Chapter 4). However, the use of conjugated polymers in electronic devices, such as light emitting diodes and field effect transistors, is very much dependent on the mobility (Skotheim, 2007, Section 2.2). Relatively higher mobility of 0.2 cm2 / V s is possible for P3HT processed and characterised in inert atmosphere, but relatively poor mobilities of 0.045 cm2 / V s emerge when the processing of P3HT OTFTs occurs under ambient conditions. In addition, regio regular P3HT is the most widely investigated PT for the fabrication of organic solar cells (Skotheim, 2007, Section 13.48). Thus, it is possible to say that P3HT is of importance in the fabrication of OTFTs and their derivatives that present many useful practical electronic applications. It is important to note that the performance of OTFTs depends on the gate insulator and active layer used (Kim, 2007, Pp. 1708 – 1712). Thus, according to the previously mentioned author, it is possible to alter the characteristic of a P3HT OTFT by properly selecting the gate insulator material. Organic insulators, including poly (vinyl phenol) (PVP), poly (vinyl alcohol) (PVA), poly (methyl metha-crylate) (PMMA), poly (9-vinyl-carbazole) (PVK), and polyimide (PI) may act as organic insulators in the P3HT based OFTFTs and this adds another dimension to the manufacturing techniques available for P3HT based OFTFTs. The tables below present differences apparent in P3HT OTFTs fabricated using various gate insulators presented by the previously mentioned author. Thus, data presented suggests that P3HT with a PVA gate insulator presented the best result for the OTFT device. Table 2: Spin Speeds and Soft Bake Conditions for each Gate Insulator, from (Kim, 2007, Pp. 1709) Table 3: Normalised C-V graphs of P3HT OTFTS using various Gate Insulators, from (Kim, 2007, Pp. 1710) Table 4: Electrical Parameters for P3HT OTFTS using various Gate Insulators, from (Kim, 2007, Pp. 1710) Table 5: Capacitance Frequency Characteristics for P3HT OTFTS using various Gate Insulators, from (Kim, 2007, Pp. 1710) Table 6: Detecting Probability for Capacitance Value Exceeding 1.0 nF / square centimetre for P3HT OTFTS using various Gate Insulators, from (Kim, 2007, Pp. 1711) It is clear that the discussion presented above that published literature suggests that P3HT is amongst the most promising of materials for the fabrication of OTFTs, OTFTs on flexible substrates and other OTFT devices. By using soluble P3HTit is possible to offers cheap fabrication costs. However, it is important to design the manufacturing process carefully to present the desired characteristics for OTFTs. (This page intentionally left blank) Bibliography/ References Fumagalli, L. Et al. (2008). Dependence on Mobility and Charge Carrier Density and Electric Field in Poly (3-hexylthiophene) (P3HT) – Based Thin Film Transistors: Effect of the Molecular Weight. Journal of Applied Physics, 104, 084513, 2008, Pp. 104 – 110. Retrieved: September 9, 2010, from: EBSCO. Janet, Lancaster. (2010). Organic MIS Devices Based on a High-k Dielectric. Bangor University. Joshi, Siddharth. (2008). Fundamental Studies of Structure and Crystallinity of Low and High Molecular Weight Poly (3-hexylthiophene) (P3HT) by Means of Synchrotron X-Ray Diffraction. Physik der Universität Siegen. Retrieved: September 9, 2010, from: http://dokumentix.ub.uni-siegen.de/opus/volltexte/2009/376/pdf/joshi.pdf Kim, Jung-Seok. Et al. (2007). Analysis of C-V Characteristics of MIS Structures using P3HT and Various Gate Insulators. Proceedings of Asia Display, Volume 2, Pp. 1708 – 1712. Retrieved: September 9, 2010, from: EBSCO. Klauk, Hagen. (2006). Organic Electronics: Materials, Manufacturing and Applications. John Wiley & Sons. Nalwa, Hari Singh, (Editor). (2001). Handbook of Advanced Electronic and Photonic Materials and Devices, Volume 8: Conducting Polymers. Academic Press. Park, Sung Kyu. (2007). High Mobility, Solution Processed Organic Thin Film Transistors. The Pennsylvania State University. Retrieved: September 9, 2010, from: http://www.scirus.com/srsapp/sciruslink?src=ndl&url=http%3A%2F%2Fetda.libraries.psu.edu%2Ftheses%2Fapproved%2FWorldWideIndex%2FETD-2145%2Findex.html Singh, Th. B. Et al. (2008). Chapter 4: Organic Field Effect Transistors: From Materials to Device Physics, in Handbook of Organic Electronics and Photonics Edited by Hari Singh Nalwa Volume 3: Pages (153-176). American Scientific Publishers. So, Frank (Editor). (2010). Organic Electronics: Materials, Processing, Devices and Applications. CRC Press. Sun, Sam-Shajing & Dalton, Larry R. (2008). Introduction to Organic Electronic and Optoelectronic Materials and Devices. CRC Press. Skotheim, Terje A. & Reynolds, John. (2007). Handbook of Conducting Polymers, Two Volume Se, Third Edition. CRC. Wiederrecht, Gary (Editor). (2010). Handbook of Nanoscale Electronics and Optics. Elsevier. William, Stephan Anak. (2006). Investigation into Memory Effect in Organic Semiconductor Devices. University of Wales, Bangor. Zong-Xiang, Xu. (2009). Organic Thin Film Transistors and Solar Cells Fabricated with π – Conjugated Polymers and Macrocyclic Materials. The University of Hong Kong, 2009. Retrieved: September 9, 2010, from: http://hub.hku.hk/handle/123456789/55567 Read More

Pure polythiophene without the side chains is neither soluble nor fusible and this means that this is not useful for making OTFTs (Joshi, 2008, Pp. 11). The previously mentioned author goes further to state that the regio regularity of P3HT, the processing methods and conditions, treatment of the gate dielectric / gate insulator and solvents used for processing of P3HT together with annealing, molecular weights affect the packaging structure of P3HT, and the type of OTFTs produced. In addition, P3HT is more readily made, and this material is, therefore, more available.

However, P3HT still presents lower manufacturing process costs and retains a strong interest for fabrication of OTFTs, despite the fact that polymers with better performance in terms of charge carrier availability are now available (Fumagalli, 2008, Pp. 104 – 105). According to Skotheim (2007, Pp. 207), a need exists for carefully designing the process of film deposition for fabrication of the OTFT and P3HT) shows much higher hole mobilities than regio random polymers and values up to 0.10–0.

30 cm2 V_1 s_1 have been claimed. Apart from the promise that P3HT shows for OTFT fabrication, this material is also suitable for fabrication of arrays of OTFTs on flexible substrates, such as for Organic Light Emitting Diode (OLED) displays (Skotheim, 2007, Chapter 4). However, the use of conjugated polymers in electronic devices, such as light emitting diodes and field effect transistors, is very much dependent on the mobility (Skotheim, 2007, Section 2.2). Relatively higher mobility of 0.

2 cm2 / V s is possible for P3HT processed and characterised in inert atmosphere, but relatively poor mobilities of 0.045 cm2 / V s emerge when the processing of P3HT OTFTs occurs under ambient conditions. In addition, regio regular P3HT is the most widely investigated PT for the fabrication of organic solar cells (Skotheim, 2007, Section 13.48). Thus, it is possible to say that P3HT is of importance in the fabrication of OTFTs and their derivatives that present many useful practical electronic applications.

It is important to note that the performance of OTFTs depends on the gate insulator and active layer used (Kim, 2007, Pp. 1708 – 1712). Thus, according to the previously mentioned author, it is possible to alter the characteristic of a P3HT OTFT by properly selecting the gate insulator material. Organic insulators, including poly (vinyl phenol) (PVP), poly (vinyl alcohol) (PVA), poly (methyl metha-crylate) (PMMA), poly (9-vinyl-carbazole) (PVK), and polyimide (PI) may act as organic insulators in the P3HT based OFTFTs and this adds another dimension to the manufacturing techniques available for P3HT based OFTFTs.

The tables below present differences apparent in P3HT OTFTs fabricated using various gate insulators presented by the previously mentioned author. Thus, data presented suggests that P3HT with a PVA gate insulator presented the best result for the OTFT device. Table 2: Spin Speeds and Soft Bake Conditions for each Gate Insulator, from (Kim, 2007, Pp. 1709) Table 3: Normalised C-V graphs of P3HT OTFTS using various Gate Insulators, from (Kim, 2007, Pp. 1710) Table 4: Electrical Parameters for P3HT OTFTS using various Gate Insulators, from (Kim, 2007, Pp. 1710) Table 5: Capacitance Frequency Characteristics for P3HT OTFTS using various Gate Insulators, from (Kim, 2007, Pp. 1710) Table 6: Detecting Probability for Capacitance Value Exceeding 1.

0 nF / square centimetre for P3HT OTFTS using various Gate Insulators, from (Kim, 2007, Pp. 1711) It is clear that the discussion presented above that published literature suggests that P3HT is amongst the most promising of materials for the fabrication of OTFTs, OTFTs on flexible substrates and other OTFT devices. By using soluble P3HTit is possible to offers cheap fabrication costs. However, it is important to design the manufacturing process carefully to present the desired characteristics for OTFTs.

(This page intentionally left blank) Bibliography/ References Fumagalli, L. Et al. (2008).

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