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Bae W.K.,Korea Institute of Science and Technology | Lim J.,Seoul National University | Lee D.,Seoul National University | Park M.,Seoul National University | And 5 more authors.
Advanced Materials | Year: 2014

Nanocrystal quantum dots (QDs) have been considered as the most promising active materials in light-emitting applications due to their advantageous optical properties, for instance, easy color tunability-ranging from near ultraviolet to visible to near infrared-narrow spectral bandwidth, and high photoluminescence quantum yield (PL QY).[1]Ever since the fi rst electrically driven quantum dot-based light-emitting devices (QLEDs) were demonstrated, [2]persistent multilateral efforts in materials synthesis [3]and a profound understanding of device physics have prompted rapid progress in the device performance (i.e., brightness, effi ciency, and stability). [4]As a result, QLEDs with improved performance down to practicable applications have been demonstrated based on structurally engineered QDs with superior optical performance and chemical stabilities along with the optimized device structure with enhanced charge carrier balance within QD active layers.[5]. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lim J.,National Creative Research Initiative Center for Intelligent Hybrids | Lee D.,Korea University | Park M.,Korea University | Song J.,Korea University | And 4 more authors.
Journal of Physical Chemistry C | Year: 2014

We demonstrate the modular fabrication of nanocrystal/polymer hybrid bulk heterojunction solar cells based on breakwater-like CdSe tetrapod (TP) nanocrystal networks infused with poly(3-hexylthiophene) (P3HT). This fabrication method consists of sequential steps for forming the hybrid active layers: the assembly of a breakwater-like CdSe TP network followed by nanocrystal surface modification and the infusion of semiconducting polymers. Such a modular approach enables the independent control of the nanoscopic morphology and surface chemistry of the nanocrystals, which are generally known to exhibit complex correlations, in a reproducible manner. Using these devices, the influence of the passivation ligands on solar cell characteristics could be clarified from temperature-dependent solar cell experiments. We found that a 2-fold increase in the short-circuit current with 1-hexylamine ligands, compared with the value based on pyridine ligands, originates from the reduced depth of trap states, minimizing the trap-assisted bimolecular recombination process. Overall, the work presented herein provides a versatile approach to fabricating nanocrystal/polymer hybrid solar cells and systematically analyzing the complex nature of these devices. © 2014 American Chemical Society.

Dirlam P.T.,University of Arizona | Simmonds A.G.,University of Arizona | Shallcross R.C.,University of Arizona | Arrington K.J.,University of Arizona | And 7 more authors.
ACS Macro Letters | Year: 2015

The synthesis of polymeric materials using elemental sulfur (S8) as the chemical feedstock has recently been developed using a process termed inverse vulcanization. The preparation of chemically stable sulfur copolymers was previously prepared by the inverse vulcanization of S8 and 1,3-diisopropenylbenzene (DIB); however, the development of synthetic methods to introduce new chemical functionality into this novel class of polymers remains an important challenge. In this report the introduction of polythiophene segments into poly(sulfur-random-1,3-diisopropenylbenzene) is achieved by the inverse vulcanization of S8 with a styrenic functional 3,4-propylenedioxythiophene (ProDOT-Sty) and DIB, followed by electropolymerization of ProDOT side chains. This methodology demonstrates for the first time a facile approach to introduce new functionality into sulfur and high sulfur content polymers, while specifically enhancing the charge conductivity of these intrinsically highly resistive materials. (Chemical Equation Presented). © 2015 American Chemical Society.

Yoon H.,National Creative Research Initiative Center for Intelligent Hybrids | Lee S.H.,Seoul National University | Sung S.H.,National Creative Research Initiative Center for Intelligent Hybrids | Suh K.Y.,Seoul National University | Char K.,National Creative Research Initiative Center for Intelligent Hybrids
Langmuir | Year: 2011

We present the mold design rules for assuring residual layer-free patterning in thermal imprint processes. Using simple relations for mass balance, structural stability, and work of adhesion, we derive the conditions with respect to the given single or multigeometrical feature of the mold, which are compared with simple thermal imprint experiments using soft imprint molds. Our analysis could serve as a guideline for designing the optimum mold geometry and selecting mold material in residual layer-free thermal imprint processes. © 2011 American Chemical Society.

Dirlam P.T.,University of Arizona | Simmonds A.G.,University of Arizona | Kleine T.S.,University of Arizona | Kleine T.S.,California Polytechnic State University, San Luis Obispo | And 11 more authors.
RSC Advances | Year: 2015

High sulfur content copolymers were prepared via inverse vulcanization of sulfur with 1,4-diphenylbutadiyne (DiPhDY) for use as the active cathode material in lithium-sulfur batteries. These sulfur-rich polymers exhibited excellent capacity retention (800 mA h g-1 at 300 cycles) and extended battery lifetimes of over 850 cycles at C/5 rate. © The Royal Society of Chemistry 2015.

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