Yoon Hee Jang

An Unconventional Route to High-Efficiency Dye-Sensitized Solar Cells via Embedding Graphitic Thin Films into TiO2 Nanoparticle Photoanode

Graphitic thin films embedded with highly dispersed titanium dioxide (TiO(2)) nanoparticles were incorporated for the first time into the conventional dye-sensitized solar cells (DSSCs), resulting in a remarkably improved cell efficiency due to its superior electron conductivity. Massively ordered arrays of TiO(2) dots embedded in carbon matrix were fabricated via UV-stabilization of polystyrene-block-poly(4-vinylpyridine) films containing TiO(2) precursors followed by direct carbonization. For dye-sensitized TiO(2) based solar cells containing carbon/TiO(2) thin layers at both sides of pristine TiO(2) layer, an increase of 62.3% [corrected] in overall power conversion efficiency was achieved compared with neat TiO(2)-based DSSCs. Such a remarkably improved cell efficiency was ascribed to the superior electron conductivity and extended electron lifetime elucidated by cyclic voltammetry and impedance spectroscopy.

On the synergistic coupling properties of composite CdS/TiO2 nanoparticle arrays confined in nanopatterned hybrid thin films

Two-dimensional (2D) arrays of hybrid CdS/TiO2 composite nanodots were fabricated on solid substrates using amphiphilic poly(styrene-block-ethylene oxide) diblock copolymer (PS-b-PEO) micelles as templates loaded with CdS nanoparticles (NPs) and TiO2 sol–gel precursors. The inorganic precursors were selectively incorporated into PEO domains of PS-b-PEO due to the specific interactions. The addition of CdS quantum dots (QDs) into thin films of the PS-b-PEO/TiO2 sol–gel mixture led to the morphological changes from mixed wire/hexagonal dot to well-defined, quasi-hexagonal dot arrays. The PS-b-PEO/TiO2/CdS system showed an enhanced absorption along with red shift behavior in the UV-visible spectral range compared with the PS-b-PEO/TiO2 films. Photoluminescence (PL) studies showed a quenching of CdS emission in the presence of TiO2. An enhanced photocatalytic degradation of methylene blue (MB) was observed in the hybrid PS-b-PEO/TiO2/CdS thin film.

Plasmonic Solar Cells: From Rational Design to Mechanism Overview

Plasmonic effects have been proposed as a solution to overcome the limited light absorption in thin-film photovoltaic devices, and various types of plasmonic solar cells have been developed. This review provides a comprehensive overview of the state-of-the-art progress on the design and fabrication of plasmonic solar cells and their enhancement mechanism. The working principle is first addressed in terms of the combined effects of plasmon decay, scattering, near-field enhancement, and plasmonic energy transfer, including direct hot electron transfer and resonant energy transfer. Then, we summarize recent developments for various types of plasmonic solar cells based on silicon, dye-sensitized, organic photovoltaic, and other types of solar cells, including quantum dot and perovskite variants. We also address several issues regarding the limitations of plasmonic nanostructures, including their electrical, chemical, and physical stability, charge recombination, narrowband absorption, and high cost. Next, we propose a few potentially useful approaches that can improve the performance of plasmonic cells, such as the inclusion of graphene plasmonics, plasmon-upconversion coupling, and coupling between fluorescence resonance energy transfer and plasmon resonance energy transfer. This review is concluded with remarks on future prospects for plasmonic solar cell use.

Visible light active photocatalysis on block copolymer induced strings of ZnO nanoparticles doped with carbon

We report a facile route for the fabrication of a unique configuration of carbon-doped strings of ZnO nanoparticles obtained by subjecting solvent vapor annealing followed by direct carbonization to reconstructed block copolymer inverse micelle arrays. The dual role of a carbon (C) moiety has been exploited in significantly enhancing the catalytic performance of C–ZnO nanohybrids under the illumination of visible light. The first role is to create a new energy level above the valence band of ZnO and the other is to act as a channel by which recombination of the excitons is effectively suppressed. The enhanced visible light active photocatalytic efficiency and recyclability of C–ZnO was demonstrated in terms of degradation of a target dye (p-nitrophenol) molecule. Photoelectrochemical water splitting was also performed using C–ZnO on ITO as the working electrode. A significant enhancement in the photocurrent density was obtained for C–ZnO compared with bare ZnO. A plausible mechanism to support the enhanced visible light activity of C–ZnO was proposed.

Synthesis and photocatalytic properties of hierarchical metal nanoparticles/ZnO thin films hetero nanostructures assisted by diblock copolymer inverse micellar nanotemplates

Metal dot-on-ZnO type hierarchical nanostructures composed of ordered arrays of noble metal nanoparticles with controlled areal density, prepared from poly(styrene-block-vinyl pyridine) diblock copolymer inverse micelles loaded with metal precursors, on sol-gel process based approximately 48 nm thick ZnO thin films exhibit enhanced photocatalytic activities compared with pure ZnO thin films in terms of photodegradation of methylene blue.

Visible-light active nanohybrid TiO2/carbon photocatalysts with programmed morphology by direct carbonization of block copolymer templates

Nanopatterned TiO2/carbon hybrid materials with tailored morphologies were produced by spin-coating solutions of amphiphilic poly(styrene-block-ethylene oxide) (PS-b-PEO) and inorganic precursors followed by sequential stabilization and carbonization. This synthetic strategy is based on cooperative sol–gel chemistry and self-assembly of block copolymers (BCPs), as well as on direct carbonization of the structure-directing BCP templates without additional carbon precursors. Thin films and powders consisting of either TiO2 dots in carbon matrices or carbon dots in TiO2 matrices as well as their powder type samples were obtained by varying the ratio of TiO2 sol–gel precursor to PS-b-PEO. X-ray photoelectron spectroscopy (XPS) revealed the formation of Ti–O–C bonds upon carbonization, as a result of additional electronic states in TiO2. The latter can be considered as the origin of the band narrowing and visible light absorption. The obtained carbon–TiO2 nanostructures showed pronounced visible-light photocatalytic activity.

Plasmonic‐Coupling‐Based Sensing by the Assembly and Disassembly of Dipycolylamine‐Tagged Gold Nanoparticles Induced by Complexing with Cations and Anions

A surface-plasmon-coupling-mediated sensor system is developed based on Au nanoparticles tagged with a coordinative dipycolylamine and lipoyl-anchored naphthalimide derivative (AuNP@DPA). The AuNPs with tailored ligands exhibit distinct sensing activity via sequential assembly into nanoparticle aggregates induced by metal ion complexing, and disassembly in the presence of pyrophosphate (PPi) anions, which is accompanied by a swift, reversible color change due to a surface plasmon resonance coupling effect. It is found that divalent metal ions are more effective than mono- or tri-valent ions in the aggregate formation process, Mn(2+)-induced aggregates are more sensitive to the capture of PPi anions than other AuNP aggregates, and the disassembly upon anion complexation exhibits a highly selective response. The AuNP@DPA-based molecular recognition system also demonstrates a viable performance for the detection of total selective metal ions present in different types of water analytes.

Localized surface plasmon resonance coupling in Au nanoparticles/phosphorus dendrimer multilayer thin films fabricated by layer-by-layer self-assembly method

Multilayer thin films of anionic gold nanoparticles (AuNPs) and cationic phosphorus dendrimers were deposited on 3-(diethoxymethyl-silyl)propylamine (3-APDMES)-coated substrates using layer-by-layer (LbL) assembly driven by electrostatic interactions. The growth of Au/dendrimer multilayers composed of AuNPs with diameters of ∼3 nm and ∼16 nm and dendrimer with ∼2 nm diameter was monitored by UV-vis spectroscopy. The relative amounts of AuNPs and dendrimers in the multilayer films were calculated using a quartz crystal microbalance. The Au-containing multilayers have two surface plasmon bands at ∼530 nm and ∼600 nm, where the latter exhibits a red shift upon increasing the areal density of AuNPs as well as increasing the layer number. The localized surface plasmon resonance (LSPR) band of the hybrid films can be tuned by adding NaCl to the dendrimer solution or by removing the organic matrix. These results demonstrate that the near-field coupling between the LSPR bands of neighboring Au layers is responsible for the controlled absorption behavior. Au mesoporous films after removing dendrimers show LSPR sensing properties for alcohols with different refractive indices in the range 1.33–1.41. A linear relationship was obtained between the LSPR peak wavelength and the refractive index of the surrounding medium.

Bimetallic Multifunctional Core@Shell Plasmonic Nanoparticles for Localized Surface Plasmon Resonance Based Sensing and Electrocatalysis

Smart bimetallic core@shell nanoparticles were fabricated based on gold nanoparticles (AuNPs) decorated with pH-sensitive polymer shell. Concretely, AuNPs having poly(4-vinylpyridine) (P4VP) on the surface were first fabricated through surface-initiated atom transfer radical polymerization (SI-ATRP). Then, they were mixed with selected metal precursor solutions followed by reduction using reducing agent. The metal NPs thus introduced were uniformly distributed in P4VP polymer shells. In order to explore the diversity and viable function of the resultant nanostructures, we controlled the size of AuNP, pH, selectivity of metal precursors, etc. We investigated the structural alteration during the sequential synthetic process. The bimetallic nanostructures of AuNP@P4VP nanocomposites containing another type of metal NP at the P4VP periphery exhibit a controlled sensing property in terms of the change in the refractive index of surrounding media and a typical electrocatalytic activity for methanol oxidation reaction.

Efficient photocatalytic hybrid Ag/TiO2 nanodot arrays integrated into nanopatterned block copolymer thin films

Well defined, ordered arrays of hybrid Ag/TiO2 hetero nanodots were fabricated on solid substrates using amphiphilic poly(styrene-block-ethylene oxide) diblock copolymer (PS-b-PEO) micelles loaded with AgNO3 and TiO2 sol–gel precursors as templates. The inorganic precursors were selectively incorporated into PEO domains due to specific chemical affinity. The conversion of AgNO3 to metallic Ag was induced by UV irradiation and confirmed by the presence of a surface plasmon band in the UV–vis absorbance spectra. The organic matrix has been removed by deep UV irradiation, leading to arrays of Ag/TiO2 composite nanoparticles (NPs). The morphology and photocatalytic activities of the resulting hybrid nanoparticle arrays were studied. Markedly enhanced photocatalytic degradation of methylene blue has been observed for Ag/TiO2 nanodot arrays compared with pure TiO2 NP arrays.