Itaru Osaka

Regioregular poly(3-alkylthiophene)s (rrP3ATs) are an important class of pi-conjugated polymers that can be used in plastic electronic devices such as solar cells and field-effect transistors. rrP3ATs can be ordered in three dimensions: conformational ordering along the backbone, pi-stacking of flat polymer chains, and lamellar stacking between chains. All of these features lead to the excellent electrical properties of these materials. Creative molecular design and advanced synthesis are critic

We report the synthesis and characterization of a novel donor-acceptor semiconducting polymer bearing naphthobisthiadiazole (NTz), a doubly benzothiadiazole (BTz)-fused ring, and its applications to organic field-effect transistors and bulk heterojunction solar cells. With NTz's highly π-extended structure and strong electron affinity, the NTz-based polymer (PNTz4T) affords a smaller bandgap and a deeper HOMO level than the BTz-based polymer (PBTz4T). PNTz4T exhibits not only high field-effect m

We show that rational functionalization of the naphthodithiophene core in copolymers based on naphthodithiophene and naphthobisthiadiazole improves the solubility without an alteration of the electronic structure. Surprisingly, the introduction of linear alkyl chains brings about a drastic change in polymer orientation into the face-on motif, which is beneficial for the charge transport in solar cells. As a result, the present polymers exhibit high power conversion efficiencies of up to ~8.2% in

A semiconducting polymer bearing the thiazolothiazole moiety in the polythiophene backbone (see figure) is synthesized. The polymer is found to have small bandgap and large ionization potential. Despite the low molecular weight, the polymer exhibited a high field-effect mobility after annealing. A high on/off ratio suggests the polymer possesses high stability against oxygen doping. The polymer device also showed good environmental stability.

The backbone orientation in the thiophene-thiazolothiazole (TzTz) copolymer system can be altered by tuning of the alky side chain composition. We highlight that the orientation significantly impact their solar cell efficiency in particular when using thicker active layers.

Owing to their superior transport properties, poly(alkylthiophenes) and their derivatives emerged as one of the most widely studied semiconducting polymers with potential applications in organic electronics. It is now generally acknowledged that one of the particularly effective ways to increase the carrier mobility in these materials is by increasing the length of the conjugated backbones. Some recent reports suggest also that carrier mobilities can be further enhanced by highly crystalline arr

Four isomeric naphthodithiophenes (NDTs) with linear and angular shapes were introduced into the polythiophene semiconductor backbones, and their field-effect transistor performances were characterized. The polymers bearing naphtho[1,2-b:5,6-b']dithiophene (NDT3), an angular-shaped NDT, exhibited the highest mobilities of ∼0.8 cm(2) V(-1) s(-1) among the four NDT-based polymers, which is among the highest reported so far for semiconducting polymers. Interestingly, the trend of the mobility in th

We have designed and synthesized novel semiconducting polymers by introducing naphtho[1,2-b:5,6-b']dithiophene (NDT) into the polythiophene backbone. These polymers, which have a highly pi-extended heteroarene unit, achieved mobilities (>0.5 cm(2) V(-1) s(-1)) that are among the highest recorded to date for semiconducting polymers and most probably result from the highly ordered thin-film structures with crystalline close pi stacking. It is noteworthy that the choice of isomeric heteroarenes in

We report the synthesis, characterization, and OFET and OPV properties of a series of novel naphthodithiophene (NDT3)-based donor-acceptor semiconducting polymers. A striking feature of the present polymers is the very close π-π stacking of 3.5 Å, most likely as a result of the large π system and the D-A system in the polymer backbone. PNDT3NTz-DT, in particular, is found to be one of the few examples of versatile polymers that exhibit both the field-effect mobility of ∼0.5 cm²/(V s)

New thiazolothiazole-thiophene copolymers show high mobilities of ∼0.1 cm2/(V s) despite the fact that the polymer chains are disordered. The polymers demonstrated excellent stability, as they maintained the initial OFET performance after 50 days in ambient air (30−50% humidity).

This review covers the progress in small-bandgap quinoid-based π-conjugated polymers, focusing on a variety of electron-deficient quinoid building units.

π-Conjugated polymers are an important class of materials for organic electronics. In the past decade, numerous polymers with donor-acceptor molecular structures have been developed and used as the active materials for organic devices, such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). The choice of the building unit is the primary step for designing the polymers. Benzochalcogenadiazoles (BXzs) are one of the most familiar acceptor building units studied in this a

In this Feature Article, we report a family of organic semiconductors based on isomeric naphthodithiophenes (NDTs). The small-molecule- and polymer-based organic semiconductors exhibit field-effect mobilities as high as 1.5 cm2 V−1 s−1 and 0.77 cm2 V−1 s−1, respectively, revealing that NDTs are useful building units for organic semiconductors. We also highlight their structure–property relationships in depth by focusing on the HOMO geometry as well as the packing structure, which provide a clear

A novel electron-deficient building unit, dithienylthienothiophenebisimide, and its polymers (PTBIs) are reported. Organic photovoltaic (OPV) cells based on PTBIs as p-type material exhibit 8.0% efficiencies with open-circuit voltages higher than 1 V. Interestingly, PTBIs also function as n-type material in OPVs depending on the molecular structure. These polymers also exhibit p-channel, n-channel, and ambipolar behaviors in field-effect transistors.

New semiconducting copolymers based on benzobisthiazole show excellent environmental stability in high-humidity air, which is an unusual performance for semiconducting polymers, along with OFET mobilities of as high as 0.26 cm2/Vs, even with disordered thin-film structures. With these unique features, these new copolymers are fascinating materials with high processability, mobility, and stability as active layers for printable electronics.