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Charging Up the Future by Organic Solar Cells
Published in Toshio Naito, Functional Materials, 2019
For example, pentacene is one of the most widely investigated organic semiconductors. In many cases, a thin film of pentacene is fabricated by vacuum deposition. Solution-processed OFETs of parent pentacene have been reported based on thermal and photochemical conversion, as shown in Fig. 8.25. The OFETs were fabricated by spin-coating of 17 and 18, followed by annealing. These devices exhibited good mobilities μh of 0.1–0.4 cm2/Vs [49, 50] The photoconversion of precursor 19 into pentacene was reported by Ono, Uno, Yamada, and coworkers at Ehime University [51, 52]. The device was fabricated as a top-contact OFET. The μh of the film is 0.34 cm2/Vs and Ion/Ioff is 2 × 106 [53]. Yamada and coworkers optimized the fabrication method by solution process and achieved a high performance, with μh of 0.86 cm2/Vs and Ion/Ioff is 4.3 × 106 [54]. This value is comparable to the vacuum-deposited OFETs of pentacene.
Humidity Sensors Based on Thin-Film and Field-Effect Transistors
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2019
However, organic TFT-based humidity sensors all have disadvantages peculiar to devices based on semiconducting polymers: bad temporal and thermal stability (Yamashita 2009), and low selectivity to water vapors. Sensors have high sensitivity to vapors of organic solvents (Torsi et al. 2003a, 2003b). For example, the major problem with pentacene, which shows the highest hole mobility of 3 cm2 V/s in thin-film TFTs, as well as many other organic conductors, is its rapid oxidation in air to form pentacene-quinone (Hasegawa and Takeya 2009). In addition, pentacene has low solubility in solvents. Good solubility is crucial for device fabrication using such solution methods as inkjet printing. Li et al. (2005) studied TFT with different p-channel OSCs and various device structures, and established that all of the p-channel OSCs investigated showed a degraded transistor performance with increased humidity. Torsi et al. (2002) found that, above 70°C, the grains in alkyl-substituted α-thiophene oligomers films begin to coalesce, and a more regular, terraced morphology with a low surface roughness is observed. This type of morphology reduced the ability of gases to adsorb, decreasing the sensor response. Slow response and recovery also must be attributed to the shortcomings of such sensors (see Figure 16.2). In addition, in many cases, the TFT parameters such as composition, doping, thickness of insulator and sensing layers, grain size, interelectrode distance, etc., are not optimized; therefore, operating characteristics of these devices are far from desired.
Fused Polycyclic Aromatic Compounds: [njAcenes, [njHelicenes, and Their Heterocyclic Analogues
Published in Atsushi Nagai, Koji Takagi, Conjugated Objects, 2017
Benzene, naphthalene, and anthracene can be extracted from coal. On the other hand, higher [n]acenes can be obtained through multistep synthesis. For examples, pentacene can be synthesized via aldol condensation between two equivalents of o-phthalaldehyde and one equivalent of 1,4-cyclohexanedione and the subsequent reduction of the obtained pentacene-6,13-dione 6 (Scheme 2.2).7 Other synthetic strategies for [n]acenes are summarized in some excellent review articles.6c
Surface-enhanced Raman spectroscopy of hexabenzobenzene, C24H12, an analogue of a graphene nanostructure
Published in Molecular Physics, 2018
Interestingly, there are a number of molecules having the one-dimensional structure of graphene that have already been chemically synthesised in large quantities and thus may have the same potential for applications. Pentacene, C22H14, which is a flat ribbon of benzene rings approximately 1.2 nm in length is one example. Thin films of pentacene have been used as the active layer in organic transistors serving as the p channel [9,10]. Another example is hexa-peri hexabenzocoronene, C42H18, (HBC) which is a flat carbon structure having a diameter of approximately 1 nm. Field-effect transistors based on derivatives of HBC have been demonstrated [11]. Hexabenzobenzene,HBZB (C24H12) is another example of such a structure.
Exploring the effect of oligothiophene and acene cores on the optoelectronic properties and enhancing p- and n-type ability of semiconductor materials
Published in Journal of Sulfur Chemistry, 2021
Ahmad Irfan, Muhammad Imran, Renjith Thomas, Muhammad Asim Raza Basra, Sami Ullah, Abdullah G. Al-Sehemi, Mohammed A. Assiri
The extremely important parameter λ is the quantity that is used for the assessment of substance ability to carry out charge [44,52]. The estimated λ value at B3LYP/6-31G** level for electron λ(e)/hole λ(h) displayed within Table 4. All studied newly designed products showed substantial effect towards lowering of λ(h) and λ(e) as compared with DTP. The Comp1-6 λ(h) as well as λ(e), were associated with well-known referenced compounds that explain the charge transport behavior of newly designed products. The theoretical values of λ(h) are 0.202, 0.045, 0.045, 0.046, 0.041, 0.030 and 0.024 eV for DTP and Comp1-6, respectively, although the λ(e) were measured as 0.228, 0.094, 0.100, 0.106, 0.109 0.081 and 0.045 eV, respectively. The computed λ(h) is smaller as compare to λ(e) within studied systems disclosing that these compounds may act as best hole transport candidates. The λ(h) of Comp1-6 are smaller than the anthra[2,3-b:7,8-b0]dithiophene and anthra[2,3-b:8,7-b0]dithiophene reference molecules, i.e. 51, 51, 50, 55, 66 and 72 meV and 40, 40, 39, 44, 55 and 61 meV, respectively [47]. The calculated results showed that pentacene is proficient hole transport substance. Gruhn et al. exhibited that λ is the crucial constituent that allows pentacene to vindicate the particularly higher hole mobility [53]. The value of λ(h) of pentacene is computed 0.098 eV [54]. The values of λ(h) of anthracene, naphthalene, along with tetracene at B3LYP/6-31G** level are 0.138, 0.186, and 0.114, respectively [36]. The results of Table 4, showed that the λ(h) of newly designed products Comp1-6 are 53, 53, 52, 57, 68 and 74 meV smaller than the pentacene, respectively enlightening that all the new designed DTP by-products could be excellent/comparable hole transport substance compared to pentacene. In the newly designed molecules, λ(h) is lower when compared to anthracene, naphthalene, tetracene and pentacene. The results demonstrated that the newly designed compounds might act as excellent hole transfer substances. It could be excellent/comparable for pentacene molecule that is frequently employed for hole transfer substance. Furthermore, the computational λ(e) of prominent used electron transport material mer-Alq3, value is 0.276 eV [55]. The results showed that values for λ(e) of Comp1-6 are 182, 176, 170, 167, 195 and 231 meV lower than the mer-Alq3 demonstrating that for these derivatives electron mobility values may be enhanced/comparable with that displayed by mer-Alq3. Thus, it is anticipated that Comp1-6 would be efficient materials to be used as p- and n-type in semiconductor devices.