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Exciton diffusion in near-infrared absorbing solution-processed organic thin films
Shin, H.-Y.,Woo, J. H.,Gwon, M. J.,Barthelemy, M.,Vomir, M.,Muto, T.,Takaishi, K.,Uchiyama, M.,Hashizume, D.,Aoyama, T.,Kim, D.-W.,Yoon, S.,Bigot, J.-Y.,Wu, J. W.,Ribierre, J. C. The Royal Society of Chemistry 2013 Physical chemistry chemical physics Vol.15 No.8
<P>We report on singlet–singlet annihilation and exciton diffusion in as-prepared p-type and annealed n-type thin films of the low-bandgap quinoidal quaterthiophene [QQT(CN)4] using ultrafast transient absorption measurements. The decay dynamics of exciton populations are well described by a one-dimensional diffusion-limited bimolecular recombination, indicating that the singlet excitons migrate preferentially along the stacking direction. Our results show that the exciton diffusion constants in QQT(CN)4 films do not vary significantly upon thermal annealing. Exciton diffusion lengths are measured to be as high as 4 and 5 nm in as-prepared and annealed QQT(CN)4 films, respectively. We also observe an influence of the excitation densities on the singlet exciton diffusion, which is attributed to phonon scattering. Because of the possibility of patterning p–n regions in QQT(CN)4 films by thermal nanolithography techniques, this study provides important insight not only into the photophysical properties of quinoidal oligothiophene derivatives but also for their future integration into high-performance p–n nanostructured near infrared light-sensing devices.</P> <P>Graphic Abstract</P><P>Exciton–exciton annihilation and exciton diffusion processes are investigated by femtosecond transient absorption in as-prepared p-type and annealed n-type thin films of the quinoidal quaterthiophene [QQT(CN)4]. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cp43705h'> </P>
Velusamy, D.B.,Kim, R.H.,Takaishi, K.,Muto, T.,Hashizume, D.,Lee, S.,Uchiyama, M.,Aoyama, T.,Ribierre, J.C.,Park, C. Elsevier Science 2014 Organic electronics Vol.15 No.11
Polymer ferroelectric-gate field effect transistors (Fe-FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next-generation non-volatile memory. For minimizing gate leakage current of a device which arises from electrically defective ferroelectric polymer layer in particular at low operation voltage, the materials design of interlayers between the ferroelectric insulator and gate electrode is essential. Here, we introduce a new solution-processed interlayer of conductive reduced graphene oxides (rGOs) modified with a conjugated block copolymer, poly(styrene-block-paraphenylene) (PS-b-PPP). A FeFET with a solution-processed p-type oligomeric semiconducting channel and ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) insulator exhibited characteristic source-drain current hysteresis arising from ferroelectric polarization switching of a PVDF-TrFE insulator. Our PS-b-PPP modified rGOs (PMrGOs) with conductive moieties embedded in insulating polymer matrix not only significantly reduced the gate leakage current but also efficiently lowered operation voltage of the device. In consequence, the device showed large memory gate voltage window and high ON/OFF source-drain current ratio with excellent data retention and read/write cycle endurance. Furthermore, our PMrGOs interlayers were successfully employed to FeFETs fabricated on mechanically flexible substrates with promising non-volatile memory performance under repetitive bending deformation.