We report highly bright and efficient inverted structure quantum dot (QD) based light-emitting diodes (QLEDs) by using solution-processed ZnO nanoparticles as the electron injection/transport layer and by optimizing energy levels with the organic hole transport layer. We have successfully demonstrated highly bright red, green, and blue QLEDs showing maximum luminances up to 23,040, 218,800, and 2250 cd/m(2), and external quantum efficiencies of 7.3, 5.8, and 1.7%, respectively. It is also noticeable that they showed turn-on voltages as low as the bandgap energy of each QD and long operational lifetime, mainly attributed to the direct exciton recombination within QDs through the inverted device structure. These results signify a remarkable progress in QLEDs and offer a practicable platform for the realization of QD-based full-color displays and lightings.

In this article, the design paradigm involving molecular weight, alkyl substituents, and donor-acceptor interaction for the poly[2,6-(4,4-bis-alkyl-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (cyclopentadithiophene-benzothiadiazole) donor-acceptor copolymer (CDT-BTZ) toward field-effect transistors (FETs) with ultrahigh mobilities is presented and discussed. It is shown that the molecular weight plays a key role in improving hole mobilities, reaching an exceptionally high value of up to 3.3 cm(2) V(-1) s(-1). Possible explanations for this observation is highlighted in conjunction with thin film morphology and crystallinity. Hereby, it is found that the former does not change, whereas, at the same time, crystallinity improved with ever growing molecular weight. Furthermore, other important structural design factors such as alkyl chain substituents and donor-acceptor interaction between the polymer backbones potentially govern intermolecular stacking distances crucial for charge transport and hence for device performance. In this aspect, for the first time we attempt to shed light onto donor-acceptor interactions between neighboring polymer chains with the help of solid state nuclear magnetic resonance (NMR). On the basis of our results, polymer design principles are inferred that might be of relevance for prospective semiconductors exhibiting hole mobilities even exceeding 3 cm(2) V(-1) s(-1).

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We present here an optimized united atom model that is able to reproduce properties of melts of n-alkane chains of varying molecular weights. This model differs from previous models in that the Lennard-Jones well depth for the terminal methyl group (0.2264 kcal/mol) differs from that of the methylene units (0.093 kcal/mol). The position of the minimum is at 4.5 Å for both units. Properties of n-C44H90 melts from this model are compared with experiments and those from an explicit atom model. Good agreement with experiment is obtained for static properties of the melt, specifically P–V–T behavior, chain conformations, and x-ray scattering profiles. The large-scale dynamics, as measured by self-diffusion, are found to agree reasonably well with experimental results, being about 30% faster with our best united atom force field. Analysis of the end-to-end vector orientation autocorrelation function in terms of the Rouse model yields a monomer friction coefficient somewhat greater than that determined from the rate of self-diffusion, reflecting the fact that the n-C44H90 chains are not sufficiently long to behave as Gaussian coils. Detailed local chain dynamics for n-C44H90 melts, as measured by the P1(t) and P2(t) orientation autocorrelation functions for C–H vectors, are found to agree reasonably well with results from simulations using an explicit atom model, and yield spin-lattice relaxation times T1 and nuclear Overhauser enhancement values in reasonable agreement with experimental 13C NMR measurements. As with large scale dynamics, local dynamics are faster in general (about 20%) than experimental results.

A comprehensive structural and electrical characterization of solution-processed blend films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) semiconductor and poly(alpha-methylstyrene) (PalphaMS) insulator was performed to understand and optimize the blend semiconductor films, which are very attractive as the active layer in solution-processed organic thin-film transistors (OTFTs). Our study, based on careful measurements of specular neutron reflectivity and grazing-incidence X-ray diffraction, showed that the blends with a low molecular-mass PalphaMS exhibited a strong segregation of TIPS-pentacene only at the air interface, but surprisingly the blends with a high molecular-mass PalphaMS showed a strong segregation of TIPS-pentacene at both air and bottom substrate interfaces with high crystallinity and desired orientation. This finding led to the preparation of a TIPS-pentacene/PalphaMS blend active layer with superior performance characteristics (field-effect mobility, on/off ratio, and threshold voltage) over those of neat TIPS-pentacene, as well as the solution-processability of technologically attractive bottom-gate/bottom-contact OTFT devices.