Kazuhiro Nakabayashi

Donor-Acceptor Block Copolymers: Synthesis and Solar Cell Applications

Fullerene derivatives have been widely used for conventional acceptor materials in organic photovoltaics (OPVs) because of their high electron mobility. However, there are also considerable drawbacks for use in OPVs, such as negligible light absorption in the visible-near-IR regions, less compatibility with donor polymeric materials and high cost for synthesis and purification. Therefore, the investigation of non-fullerene acceptor materials that can potentially replace fullerene derivatives in OPVs is increasingly necessary, which gives rise to the possibility of fabricating all-polymer (polymer/polymer) solar cells that can deliver higher performance and that are potentially cheaper than fullerene-based OPVs. Recently, considerable attention has been paid to donor-acceptor (D-A) block copolymers, because of their promising applications as fullerene alternative materials in all-polymer solar cells. However, the synthesis of D-A block copolymers is still a challenge, and therefore, the establishment of an efficient synthetic method is now essential. This review highlights the recent advances in D-A block copolymers synthesis and their applications in all-polymer solar cells.

Novel Complex Polymers with Carbazole Functionality by Controlled Radical Polymerization

This review summarizes recent advances in the design and synthesis of novel complex polymers with carbazole moieties using controlled radical polymerization techniques. We focus on the polymeric architectures of block copolymers, star polymers, including star block copolymers and miktoarm star copolymers, comb-shaped copolymers, and hybrids. Controlled radical polymerization of N-vinylcarbazole (NVC) and styrene and (meth)acrylate derivatives having carbazole moieties is well advanced, leading to the well-controlled synthesis of complex macromolecules. Characteristic optoelectronic properties, assembled structures, and three-dimensional architectures are briefly introduced.

Synthesis and characterization of poly(phenylene thioether)s containing pyrimidine units exhibiting high transparency, high refractive indices, and low birefringence

Novel poly(phenylene thioether)s containing pyrimidine rings and fluorene units in the main chain have been developed as promising candidates for thermoplastic lenses which are used for compensating chromatic aberration. The obtained polymers showed a good thermal stability (i.e., 5% weight-loss temperature over 320 °C) and relatively high glass transition temperatures in the range of 132–201 °C. The cutoff wavelengths of the polymer thin films are shorter than 320 nm, and a transmittance higher than 90% was observed over 380 nm. The polymer containing a fluorene unit with the highest sulfur content exhibited the highest refractive index of 1.678 and the low birefringence of 0.004 at 633 nm.

All-Polymer solar cells based on fully conjugated donor-acceptor block copolymers with poly(naphthalene bisimide) acceptor blocks: device performance and thin film morphology

All-polymer solar cells are fabricated by using poly (3-hexylthiophene) (P3HT) and fully conjugated donor-acceptor (D-A) block copolymer (P3HT-PNBI-P3HT) as donor and acceptor materials, respectively. Atomic force microscopy (AFM) and grazing incidence wide angle X-ray scattering (GIWAXS) analyses reveal that device performance strongly depends on the P3HT: P3HTPNBI- P3HT thin film morphology. Indeed, the Π-Π stacking nanomorphology rich in the edge-on orientation is formed in the P3HT:P3HT-PNBI-P3HT thin film by optimizing the fabrication conditions, for example, thermal annealing temperature and cast solvent. Consequently, the power conversion efficiency (PCE) of 1.60% is achieved with an open-circuit voltage (Voc) of 0.59 V, short-current (Jsc) of 4.43 mA/cm2, and fill factor (FF) of 0.61. These results suggest that P3HT-PNBI-P3HT has the huge potential for the usage as a nonfullerene acceptor material.

Direct arylation polycondensation as conjugated polymer synthesis methodology

AbstractDirect arylation polymerization (DArP), which is a cross-coupling polymerization between a dihaloarene monomer and a non-substituted arene monomer, has attracted widespread attention for conjugated polymer synthesis. In DArP, no prior preparation of arene monomers with organometallic functionalities is necessary, in contrast to typical cross-coupling polymerizations such as the Suzuki and Stille reactions. Furthermore, the low toxicity of the byproducts of DArP contributes to green chemistry. In terms of efficiency and environmental friendliness, these advantages make DArP an attractive next-generation polymer synthetic method. To date, numerous conjugated polymers have been synthesized by DArP. However, many problems remain to be overcome, including better understanding of the correlation between polymer structure and DArP factors, the design of a more efficient DArP system, and so on. Addressing these problems could lead to the establishment of DArP as a viable alternative for conjugated polymer synthesis. We revealed that a variety of conjugated polymers such as donor–acceptor alternating copolymers (arylene diimide-based donor–acceptor alternating copolymers and thienoisoindigo-based donor-acceptor alternating copolymers) and regioregular poly(3-alkylselenophene)s were successfully synthesized by the DArP strategy based on appropriate molecular design and adjustment of the catalytic system. This focus review will describe our recent studies developing the synthesis of novel conjugated polymers via DArP.Our recent studies on the development of conjugated polymer synthesis via direct arylation polycondensdation (DArP) are summarized. Based on an appropriate molecular design and adjustment of the catalytic system for DArP, a variety of conjugated polymers, such as low-band-gap polymers with the strong acceptor moieties and regioregular poly(3-hexylselenophene) are successfully synthesized. These results demonstrate potential and utility of DArP as an alternative conjugated polymer synthesis methodology.