Yoshimasa Sakai

Solution-processible organic semiconductor for transistor applications: Tetrabenzoporphyrin

We report an organic semiconductor, tetrabenzoporphyrin, that can be used for transistor applications. It can be derived from a soluble precursor compound with bicyclo structure. The precursor film is amorphous and shows good film morphology. Then it is converted into an insoluble crystalline semiconductor film quantitatively at elevated temperature of 150–200 °C. Field-effect transistors were fabricated by this method. Observed mobility of the devices exceeded 10−2 cm2/V s with appropriate process and device structure.

Organic Field-Effect Transistor Devices Based on Latent Pigments of Unsubstituted Diketopyrrolopyrrole or Quinacridone

Organic field-effect transistors (FETs) based on unsubstituted diketopyrrolopyrrole (DPP) or quinacridone (QA) have been fabricated using their solvent-soluble precursors called latent pigments (t-BOC DPP and t-BOC QA) which can also be regenerated into their parent pigments by heating at about 200 °C. The use of latent pigments enables us to fabricate FETs by spin coating, offering a low-cost fabrication process rather than an expensive vacuum technology. The objective of the present investigation is to evaluate the performance of DPP- and QA-based FETs prepared using latent pigments. As a result, field effect mobilities of about 7.19×10-6 and 8.23×10-6 cm2 V-1 s-1 are obtained for FETs based on t-BOC DPP and QA, respectively. These values are almost equivalent to those of FETs prepared by the vacuum deposition of DPP and QA, namely 1.43×10-5 and 1.08×10-5 cm2 V-1 s-1, respectively. The present result leads us to conclude that latent pigment technology is an excellent low-cost process fabricating organic FETs.

2,8- and 2,9-Diboryltetracenes as Useful Building Blocks for Extended π-Conjugated Tetracenes

Ir-catalyzed direct diborylation of tetracene gave a 1:1 mixture of 2,8- and 2,9-bis[(pinacolato)boryl]tetracenes, which were separated by recrystallization. These diboryltetracenes are useful building blocks for the regiospecific synthesis of extended pi-conjugated tetracenes directed to semiconductors for organic field-effect transistors (OFETs). Syntheses of thiophene-tetracene-thiophene, thiophene-tetracene-bithiophene-tetracene-thiophene, and thiophene-tetracene-anthracene-tetracene-thiophene pi-systems have been achieved on the basis of the 2,8- and 2,9-diboryltetracenes.

Bis(methylthio)tetracenes: Synthesis, Crystal-Packing Structures, and OFET Properties

5,12-Bis(methylthio)tetracene (2) and 5,11-bis(methylthio)tetracene (3) were synthesized. DFT calculations indicate that the HOMO and LUMO energy levels of 2 and 3 are lowered by 0.13-0.24 eV and their HOMO-LUMO energy gaps are reduced by 0.1 eV relative to those of tetracene. X-ray crystallographic data revealed that 2 is arranged as a result of a 1-D slipped-cofacial π-stacking with S-S and S-π interactions, similar to the packing arrangement of 6,13-bis(methylthio)pentacene (1), whereas 3 exhibits a herringbone packing arrangement without S-S interactions. The OFET devices fabricated using spin-coated films of soluble 1 and 2, with a bottom-contact device configuration, exhibited hole mobilities as high as 1.3 × 10(-2) and 4.0 × 10(-2) cm(2) V(-1) s(-1) with current on/off ratios of over 10(5) and 10(4), respectively.

Tetrabenzoporphyrin semiconductor for transistor applications

An organic field effect transistor (FET) device based on a solution-processible tetrabenzoporphyrin (BP) has been developed. BP is derived from its precursor that is soluble in some organic solvents and gives an amorphous film of high quality by spin coating. A polycrystalline film of BP is obtained by thermal conversion of the precursor at about 200 degree C. The FET characteristics are found to largely depend on the purity, device structure, and fabrication process. The device performance was: mobility of 1.7 X 10-2 cm2/Vs and on/off ratio of 105. We have also analyzed the crystal structure of BP and characterized its electronic and morphological properties.

Direct patterning of poly(3-hexylthiophene) and its application to organic field-effect transistor

A direct photolithographic patterning method of regioregular poly(3-hexylthiophene) (rr-P3HT) as a semiconductive layer of organic field-effect transistors (OFETs) has been developed. The performance (0.092 cm2/Vs) of a bottom-contact type OFET using the patterned rr-P3HT as a semiconductive layer was almost the same as that (0.10 cm2/Vs) using the pristine rr-P3HT.

Crystal structure of parallel-stacked peryleneimides and their application to organic field-effect transistor devices

Organic field-effect transistors (FETs) have recently attracted attention mainly because of the low fabrication cost. Parallel-stacked structure is considered favorable for realizing a high mobility along the stacked direction in organic FETs. Among our dipyridyl-peryleneimides synthesized previously for H2 sensors (OPP, MPP, and PPP for o-, m-, and p-position of the N atom in the pyridyl ring, respectively), OPP and PPP are found to crystallize in this structure and are expected to show better FET characteristics than MPP. Therefore, the FET characteristics have been studied in the present investigation from the standpoint of the crystal structure. The FET devices based on OPP and PPP exhibit n-type characteristics, showing a mobility of about 10−5cm2∕(Vs) and “on/off” ratios of about 102, whereas only poor performance was observed for the MPP-based FET.

(1RS,4SR,8SR,11RS,15SR,18RS,22RS,25SR)-1,4 : 8,11 : 15,18 : 22,25-tetraethano-29H,31H-tetrabenzo[b,g,l,q]porphine chloroform disolvate

In the title compound, C44H38N4·2CHCl3, the porphine (CP) is a soluble precursor of metal-free porphyrin which exhibits an excellent field-effect transistor characteristic. The CP skeleton is entirely flat and characterized by crystallographic Ci symmetry. In the present geometrical isomer, the C—C single-bond linkages of the four peripheries are arranged in an above–above–below–below manner with respect to the CP skeleton.