We report the synthesis and polymerization of a novel thieno[3,2-b]thiophene-diketopyrrolopyrrole-based monomer. Copolymerization with thiophene afforded a polymer with a maximum hole mobility of 1.95 cm(2) V(-1) s(-1), which is the highest mobility from a polymer-based OFET reported to date. Bulk-heterojunction solar cells comprising this polymer and PC(71)BM gave a power conversion efficiency of 5.4%. 相似文献
In the nonparametric regression models, a homoscedastic structure is usually assumed. However, the homoscedasticity cannot be guaranteed a priori. Hence, testing the heteroscedasticity is needed. In this paper we propose a consistent nonparametric test for heteroscedasticity, based on wavelets. The empirical wavelet coefficients of the conditional variance in a regression model are defined first. Then they are shown to be asymptotically normal, based on which a test statistic for the heteroscedasticity is constructed by using Fan's wavelet thresholding idea. Simulations show that our test is superior to the traditional nonparametric test. 相似文献
We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt % 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C61 (PCBM). Three polymers are observed to give amorphous films, attributed to a nonplanar geometry of their backbone while the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (approximately 100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt % PCBM resulted in 70-90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissociated polymer+ and PCBM- polarons, assayed by the appearance of a long-lived, power-law decay phase assigned to bimolecular recombination of these polarons, was observed to vary by over 2 orders of magnitude depending upon the polymer employed. In addition to this power-law decay phase, the blend films exhibited short-lived decays assigned, for the amorphous polymers, to neutral triplet states generated by geminate recombination of bound radical pairs and, for the more crystalline polymers, to the direct observation of the geminate recombination of these bound radical pairs to ground. These observations are discussed in terms of a two-step kinetic model for charge generation in polythiophene/PCBM blend films analogous to that reported to explain the observation of exciplex-like emission in poly(p-phenylenevinylene)-based blend films. Remarkably, we find an excellent correlation between the free energy difference for charge separation (deltaG(CS)rel) and yield of the long-lived charge generation, with efficient charge generation requiring a much larger deltaG(CS)rel than that required to achieve efficient PL quenching. We suggest that this observation is consistent with a model where the excess thermal energy of the initially formed polaron pairs is necessary to overcome their Coulombic binding energy. This observation has important implications for synthetic strategies to optimize organic solar cell performance, as it implies that, at least devices based on polythiophene/PCBM blend films, a large deltaG(CS)rel (or LUMO level offset) is required to achieve efficient charge dissociation. 相似文献
By comparing the changes in pi-pi* absorption with the transconductance in PEO-LiClO4 electrolyte-gated FETs, we have demonstrated that the high channel currents obtained at low gate voltages result from reversible electrochemical doping of the semiconducting polymer film. At low temperatures, the conductivity of the electrochemically doped poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT-C14, is nonlinear with a crossover from dsigma(T)/dT > 0 to dsigma(T)/dT approximately 0 as a function of the source-drain voltage. High current densities, up to 10(6) A/cm2 at 4.2 K, can be sustained in the electrochemically doped PBTTT-C14 films. 相似文献
We study the appearance and energy of the charge transfer (CT) state using measurements of electroluminescence (EL) and photoluminescence (PL) in blend films of high-performance polymers with fullerene acceptors. EL spectroscopy provides a direct probe of the energy of the interfacial states without the need to rely on the LUMO and HOMO energies as estimated in pristine materials. For each polymer, we use different fullerenes with varying LUMO levels as electron acceptors, in order to vary the energy of the CT state relative to the blend with [6,6]-phenyl C61-butyric acid methyl ester (PCBM). As the energy of the CT state emission approaches the absorption onset of the blend component with the smaller optical bandgap, E(opt,min) ≡ min{E(opt,donor); E(opt,acceptor)}, we observe a transition in the EL spectrum from CT emission to singlet emission from the component with the smaller bandgap. The appearance of component singlet emission coincides with reduced photocurrent and fill factor. We conclude that the open circuit voltage V(OC) is limited by the smaller bandgap of the two blend components. From the losses of the studied materials, we derive an empirical limit for the open circuit voltage: V(OC) ? E(opt,min)/e - (0.66 ± 0.08)eV. 相似文献
We establish a setting-atoms in optical superlattices with period 2-in which one can experimentally probe signatures of the process of local relaxation and apparent thermalization in nonequilibrium dynamics without the need of addressing single sites. This opens up a way to explore the convergence of subsystems to maximum entropy states in quenched quantum many-body systems with present technology. Remarkably, the emergence of thermal states does not follow from a coupling to an environment but is a result of the complex nonequilibrium dynamics in closed systems. We explore ways of measuring the relevant signatures of thermalization in this analogue quantum simulation of a relaxation process, exploiting the possibilities offered by optical superlattices. 相似文献
A series of selenophene oligomers incorporating conjugated fluorinated phenylene units have been synthesised as potential semiconductor materials for organic field‐effect transistors (OFETs). X‐ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, making them ideal candidates for OFET applications.
Alkali metal–oxygen batteries are of great interests for energy storage because of their unparalleled theoretical energy densities. Particularly attractive is the emerging Na–O2 battery because of the formation of superoxide as the discharge product. Dimethyl sulfoxide (DMSO) is a promising solvent for this battery but its instability towards Na makes it impractical in the Na–O2 battery. Herein we report the enhanced stability of Na in DMSO solutions containing concentrated sodium trifluoromethanesulfonimide (NaTFSI) salts (>3 mol kg?1). Raman spectra of NaTFSI/DMSO electrolytes and ab initio molecular dynamics simulation reveal the Na+ solvation number in DMSO and the formation of Na(DMSO)3(TFSI)‐like solvation structure. The majority of DMSO molecules solvating Na+ in concentrated solutions reduces the available free DMSO molecules that can react with Na and renders the TFSI anion decomposition, which protects Na from reacting with the electrolyte. Using these concentrated electrolytes, Na–O2 batteries can be cycled forming sodium superoxide (NaO2) as the sole discharge product with improved long cycle life, highlighting the beneficial role of concentrated electrolytes for Na‐based batteries. 相似文献