Search

We analyzed the effects of air leakage and other building characteristics on outdoor particle penetration in classrooms. The building characteristics including air leakage of 12 Korean schools were investigated, and onsite measurements were conducted to estimate the outdoor particle infiltration. The correlations among variables associated with air leakage and building characteristics and outdoor particle infiltration were analyzed using the Pearson correlation analysis and linear regression. The effective leakage area (ELA) of classrooms varied highly from 340.8–1566.9 cm2, and a significant disparity in the air leakage characteristics among the classrooms appeared. The results of onsite measurement revealed that the average ELA was larger in the corridor side with an ELAcorridor-side of 264.7 cm2 than in the outdoor side (ELAoutdoor-side of 93.1 cm2). Results of correlation analysis indicated a high correlation (r = 0.68~0.78, p-value &lt, 0.05) between the size resolved outdoor particle source (P × λ) and specific ELA. Particularly, a strong linear relation (R2 = 0.69~0.71) with specific ELAcorridor-side was seen. Results suggest that cracks between windows and doors in the corridor side considerably affect outdoor particle penetration. These results indicate the importance of improving the airtightness of not only the building envelope but also the inter-zonal walls for effectively reducing the outdoor particle infiltration into classrooms.

Perovskite solar cells (PSCs) require both high efficiency and good long-term stability if they are to be commercialized. It is crucial to finely optimize the energy level matching between the perovskites and hole-transporting materials to achieve better performance. Here, we synthesize a fluorene-terminated hole-transporting material with a fine-tuned energy level and a high glass transition temperature to ensure highly efficient and thermally stable PSCs. We use this material to fabricate photovoltaic devices with 23.2% efficiency (under reverse scanning) with a steady-state efficiency of 22.85% for small-area (~0.094 cm2) cells and 21.7% efficiency (under reverse scanning) for large-area (~1 cm2) cells. We also achieve certified efficiencies of 22.6% (small-area cells, ~0.094 cm2) and 20.9% (large-area, ~1 cm2). The resultant device shows better thermal stability than the device with spiro-OMeTAD, maintaining almost 95% of its initial performance for more than 500 h after thermal annealing at 60 °C. Interfacial losses between device layers play a key role in determining characteristics of solar cells. Jeon et al. address this in perovskite solar cells by synthesizing a hole-transporting layer that is better matched to the surrounding layers, and show high-efficiency and high-stability devices.

We present phosphorescence enhancement of 2,5-dihexyloxy-4-bromobenzaldehyde (Br6A), a metal-free organic phosphor, by means of Ag nanoparticles (NPs) through surface plasmon excitation. The emission enhancement and lifetime reduction was observed in the fluorescence and phosphorescence suggesting that the phosphorescence enhancement can be achieved in the same manner as in fluorescence, through the increase of photoabsorption and the enhanced emission rate by the field enhancement around the metal nanostructures. Our results help to improve the understanding of the phosphorescence enhancement mechanism of a new class of purely organic phosphors.

Three novel triarylamine derivatives (TPACs: TPAC0M, TPAC2M and TPAC3M), sharing the same conjugation scaffold but possessing different numbers of methoxy units, were designed for high performance hole transport materials (HTMs) of p–i–n planar perovskite solar cells (PSCs). Cyclic voltammetry and absorption results showed that their energy levels would be beneficial to work as HTMs of PSCs, and time-resolved photoluminescence and transient photo-voltage studies proved that TPAC-based PSCs had better charge extraction and more suppressed non-radiative recombination properties than PEDOT:PSS-based PSCs, leading to superior power conversion efficiency (PCE). We confirmed that the methoxy units introduced to the triarylamine derivatives did not cause noticeable changes in their optical properties, such as absorption and bandgap, electrical conductance, measured by conductive atomic force microscopy, and mobility, but the charge extraction and recombination behaviors of TPAC-based PSCs could be improved by increasing the number of methoxy units in the arylamine moiety. X-ray photoelectron spectroscopy revealed that methoxy units could act as a Lewis base passivating the defect sites at the interface between HTM and perovskite, consequently resulting in an increase of their PCE to 17.54% without any dopants.

Perovskite solar cells (PSCs) with mesoporous TiO2 (mp‐TiO2) as the electron transport material attain power conversion efficiencies (PCEs) above 22%; however, their poor long‐term stability is a critical issue that must be resolved for commercialization. Herein, it is demonstrated that the long‐term operational stability of mp‐TiO2 based PSCs with PCE over 20% is achieved by isolating devices from oxygen and humidity. This achievement attributes to systematic understanding of the critical role of oxygen in the degradation of PSCs. PSCs exhibit fast degradation under controlled oxygen atmosphere and illumination, which is accompanied by iodine migration into the hole transport material (HTM). A diffusion barrier at the HTM/perovskite interface or encapsulation on top of the devices improves the stability against oxygen under light soaking. Notably, a mp‐TiO2 based PSC with a solid encapsulation retains 20% efficiency after 1000 h of 1 sun (AM1.5G including UV) illumination in ambient air.

The present research is focused to investigate a role of the porous graphite (PG) plate that could improve the quality of 4H-SiC crystal. The grown crystal in porous graphite inserted crucible showed the lower intensity of Al, B and Ti impurity concentration than SiC crystal grown in conventional crucible. The porous graphite plate before and after the growth process has been investigated by a Raman spectroscopy and a photoluminescence spectrum (PL). According to the analysis result, it was confirmed that the porous graphite plate had the effect of suppressing impurities supplied to SiC single crystal during the growth process.

Highly transparent and nanostructured nickel oxide (NiO) films through pulsed laser deposition are introduced for efficient CH3 NH3 PbI3 perovskite solar cells. The (111)-oriented nanostructured NiO film plays a key role in extracting holes and preventing electron leakage as hole transporting material. The champion device exhibits a power conversion efficiency of 17.3% with a very high fill factor of 0.813.

The effect of the porous graphite plate above the source material on properties of silicon carbide (SiC) crystals grown by Physical Vapor Transport method has been investigated. The porous graphite plate was inserted on source powder to produce a more C-rich for the polytype stability of 4H-SiC crystal and a uniform radial temperature gradient. The dendrite structure obtained from SiC source powder in the crucible with porous graphite plate was more densely formed than that in the conventional crucible. The crystal quality of 4H-SiC single crystals grown in porous graphite inserted crucible was revealed to be better than that of crystal grown SiC crystals in the conventional crucible.

The present research is focused on the effect of porous graphite what is influenced on the 4H-SiC crystal growth by PVT method. We expect that it produces more C-rich and a change of temperature gradient for polytype stability of 4H-SiC crystal as adding the porous graphite in the growth cell. The SiC seeds and high purity SiC source materials were placed on opposite side in a sealed graphite crucible which was surrounded by graphite insulator. The growth temperature was around and the growth pressure was 10~30 Torr of an argon pressure with 5~15 % nitrogen. 2 inch off-axis 4H-SiC with C-face (000-1) was used as a seed material. The porous graphite plate was inserted on SiC powder source to produce a more C-rich for polytype stability of 4H-SiC crystal and uniform radial temperature gradient. While in case of the conventional crucible, various polytypes such as 6H-, 15R-SiC were observed on SiC wafers, only 4H-SiC polytype was observed on SiC wafers prepared in porous graphite inserted crucible. The defect level such as MP and EP density of SiC crystal grown in the conventional crucible was observed to be higher than that of porous graphite inserted crucible. The better crystal quality of SiC grown using porous graphite plate was also confirmed by rocking curve measurement and Raman spectra analysis.

The infrared and Raman spectra of vapor-phase and liquid-phase benzocyclobutane (BCB) have been recorded and assigned. The structure of the molecule was calculated using the MP2/cc-pVTZ basis set and the vibrational frequencies and spectral intensities were calculated using the B3LYP/cc-pVTZ level of theory. The agreement between experimental and calculated spectra is excellent. In order to allow comparisons with related molecules, ab initio and DFT calculations were also carried out for indan (IND), tetralin (TET), 1,4-benzodioxan (14BZD), 1,3-benzodioxan (13BZD) and 1,4-dihydronaphthalene (14DHN). The ring-puckering, ring-twisting, and ring-flapping vibrations were of particular interest as these reflect the rigidity of the bicyclic ring system. The infrared spectra of BCB show very nice examples of vapor-phase band types and combination bands.

Perovskite solar cells are promising candidates for realizing an efficient, flexible, and lightweight energy supply system for wearable electronic devices. For flexible perovskite solar cells, achieving high power conversion efficiency (PCE) while using a low-temperature technology for the fabrication of a compact charge collection layer is a critical issue. Herein, we report on a flexible perovskite solar cell exhibiting 12.2% PCE as a result of the employment of an annealing-free, 20 nm thick, amorphous, compact TiOx layer deposited by atomic layer deposition. The excellent performance of the cell was attributed to fast electron transport, verified by time-resolved photoluminescence and impedance studies. The PCE remained the same down to 0.4 sun illumination, as well as to a 45° tilt to incident light. Mechanical bending of the devices worsened device performance by only 7% when a bending radius of 1 mm was used. The devices maintained 95% of the initial PCE after 1000 bending cycles for a bending radius of 10 mm. Degradation of the device performance by the bending was the result of crack formation from the transparent conducting oxide layer, demonstrating the potential of the low-temperature-processed TiOx layer to achieve more efficient and bendable perovskite solar cells, which becomes closer to a practical wearable power source.

Sulfonated hollow microporous organic polymers (S-HMOP) were prepared by template synthesis and post synthetic approach. The S-HMOP showed excellent non-covalent fixation ability towards various cationic dyes through ionic interaction. Among various dye systems, Zn-porphyrin loaded S-HMOP showed promising activity and stability in the decomposition of 4-chlorophenol under visible light irradiation.

Sn-porphyrin networks were engineered on the surface of a thin layer chromatography (TLC) plate via Sonogashira coupling of the Sn-porphyrin building block and 1,4-diiodobenzene. The Sn-porphyrin film showed a strong Soret band absorption at 422 nm, emission at 600-630 nm, and excellent sensing performance toward nitrophenols in water.

Novel iridium(III) complexes containing bis(N-heterocyclic carbene), bis(imidazoline thione) L2, and bis(imidazoline selone) L3 were prepared. The iridium complexes bearing L2 and L3 showed the significant absorption of visible light with maximum intensity at ∼460 nm. Bis(2-(2′-benzothienyl)pyridinato)iridium(III) complexes (Ir-6) with L3 showed excellent ability as a photosensitizer of visible light. Under blue LED irradiation with maximum emission at 460 nm, 0.25 mol % Ir-6 showed 94% conversion of benzylamine for 5 h at room temperature. Through mechanistic studies, it was suggested that the photoinduced oxidative coupling of benzylamine by Ir-6 follows a singlet oxygen pathway. The excellent performance of Ir-6 originated from the efficient visible light absorption at 460 nm and the enhanced triplet state due to the heavy-atom effect of L3. This work shows that bis(imidazoline thione) and bis(imidazoline selone) can be efficient ligands for tuning the optical properties of iridium(III) complexes.

The nanoporous alumina membranes (NAMs) were fabricated by a two-step aluminium anodic oxidation process. The fabricated NAMs have controllable pore diameters (40–80 nm) and unidirectionally ordered pore direction. The surface of the NAM was modified with the organo-silane agent (APTES: (aminopropyl)triethoxysilane) to induce ionic bonding between the NAM and the photosensitizer (TSPP: tetrakis(p-sulfonatophenyl)porphyrin). The morphology and chemical nature of the surface modified NAM were studied by field emission scanning electron microscope (FE-SEM), FT-IR spectra, and thermo gravimetric analysis (TGA). Furthermore, this singlet oxygen generating nanoporous membranes (SGNMs) were investigated, in detail, to understand their photophysical properties and the singlet oxygen generation efficiency which were the essential factors for their applications. Steady-state spectroscopies and nanosecond laser induced time-resolved spectroscopy were applied to get information on all photophysical properties including the lifetime of singlet oxygen which depended on the pore diameter of the SGNM.

Multifunctional SiO 2 particles with charged and fluorescent properties were synthesized and their films with different thickness were prepared using electrophoretic deposition for random lasing. In case of 50-μm-thick film, when the excitation energy density increases above 25 μJ/cm 2 , spectral narrowing and nonlinear increasing of intensity were observed. To get more information on lasing, single-shot spectrum was measured. Finally, the dependence of the lasing behavior, including the recognition of the existence of a threshold on the film thickness was demonstrated.

Although significant progress has been made in the development of vacuum-deposited small-molecule organic light-emitting diodes (OLEDs), one of the most desired research goals is still to produce flexible displays by low-cost solution processing. The development of solution-processed OLEDs based on small molecules could potentially be a good approach but no intensive studies on this topic have been conducted so far. To fabricate high-performance devices based on solution-processed small molecules, the underlying nature of the produced films and devices must be elucidated. Here, the distinctive characteristics of solution-processed small-molecule films and devices compared to their vacuum-deposited counterparts are reported. Solution-processed blue OLEDs show a very high luminous efficiency (of about 8.9 cd A–1) despite their simplified structure. A better hole-blocking and electron-transporting layer is essential for achieving high-efficiency solution-processed devices because the solution-processed emitting layer gives the devices a better hole-transporting capability and more electron traps than the vacuum-deposited layer. It is found that the lower density of the solution-processed films (compared to the vacuum-deposited films) can be a major cause for the short lifetimes observed for the corresponding devices.

A fluorescing, copolymer (Q)-bearing, quaternary ammonium pendant was mixed with excess natural salmon sperm DNA with a molecular weight of 1.3×106 (2,000 base pairs) to afford highly fluorescing, complex mixtures. The fluorescence life-time of the polymer Q was greatly increased when mixed with DNA: for the mixture of Q:DNA=1:750 the fast and slow decay lifetimes increased from ca. 10 to 100 ps and from 20 ps to ca. 1 ns, respectively. The enhanced fluorescence of the mixtures was ascribed to efficient compartmentalization and reduced conformational relaxation of the polymer Q by complexation with excess DNA.

The effect of the interfacial interaction between host−guest materials on energy transfer efficiency was investigated. Porous alumina membrane (PAM) was used as the host, and poly(N-vinylcarbazole) (PVK) and tris(8-hydroxyquinoline) aluminum (Alq3) were guest materials. The energy transfer between PVK and Alq3 within a PAM shows greatly enhanced efficiency compared with that of the bulk film. Such high efficiency is ascribed to a lowered formation of the fully overlapped form of the PVK excimer, which is induced by strong interaction between the pendant carbazole rings of PVK and the Al centers on the innerchannel surface of the PAM. The photoluminescence lifetimes of PVK become shorter with an increase in the Alq3 concentration in both films and PAMs, due to the energy transfer. The mean distance between PVK and Alq3 was estimated by using the Forster formula.

To understand the role of the dye/oxide interface, a model system using a nanocrystalline SnO2 and 3-hexyl thiophene based MK-2 dye is proposed. A thin interfacial TiO2 blocking layer (IBL) is introduced in between SnO2 and MK-2 and its effects on photocurrent–voltage, electron transport-recombination, and density of states (DOS) are systematically investigated. Compared to the bare SnO2 film, the insertion of IBL leads to a 14-fold improvement in the power conversion efficiency (PCE) despite little change in the dye adsorption amount, which is due to the 7-fold and 2-fold increase in the photocurrent density and voltage, respectively. The charge collection efficiency is substantially improved from 38% to 96% mainly due to the increase in the electron lifetime. The IBL is also found to enhance the dye regeneration efficiency as confirmed by the 15-fold faster dye bleaching recovery dynamics. The recombination resistance increases and the DOS decreases after surface modification of SnO2, which is responsible for the doubly increased voltage. This study suggests that the interfacial layer between the oxide and the dye plays a crucial role in retarding recombination, improving charge collection efficiency, increasing diffusion length, accelerating dye regeneration and narrowing the density of states.

We report on the direct growth of anatase TiO2 nanorod arrays (A-NRs) on transparent conducting oxide (TCO) substrates that can be directly applied to various photovoltaic devices via a seed layer mediated epitaxial growth using a facile low-temperature hydrothermal method. We found that the crystallinity of the seed layer and the addition of an amine functional group play crucial roles in the A-NR growth process. The A-NRs exhibit a pure anatase phase with a high crystallinity and preferred growth orientation in the [001] direction. Importantly, for depleted heterojunction solar cells (TiO2/PbS), the A-NRs improve both electron transport and injection properties, thereby largely increasing the short-circuit current density and doubling their efficiency compared to TiO2 nanoparticle-based solar cells.

Photochromic diarylethene polymers (DPs) in which 1,2-bis(2-methylbenzo[b]thiophene-3-yl)hexafluorocyclopentene (BTF6) were covalently grafted onto the polymer main chain as pendant photochromic units were newly synthesized and their photochromic properties were investigated using steady-state and picosecond timeresolved spectroscopies. Polysiloxanes substituted with BTF6 molecules were prepared by sol-gel process using a mixture of tetraethoxysilane (TEOS), a silylated BTF6, and an organically modified silane precursor in the presence of HCl. The polysiloxane film (DP1) prepared from ω-methoxy poly(ethylene glycol) 3-(triethoxysilyl) propylcarbamate (MPGSC) as the silane precursor showed a much lower glass transition temperature than that (DP2) from heptadecafluorodecyltrimethoxysilane (HDFTMS). The ring-closure quantum yields ofDP1 andDP2 were determined to be 0.20 and 0.02, respectively. Such a large difference in the quantum yield was attributed to the polymer matrix environment of the free inner volume.

A series of copolymers, poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4-dicyanomethylene-2-methyl-6-[4-(diphenylamino)styryl]-4H-pyran-4‘,4‘ ‘-diyl)], were synthesized by polymerizing 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene with mixtures of 2,7-dibromo-9,9-dioctylfluorene and 4-dicyanomethylene-2-methyl-6-[bis(4‘-bromophenyl)amino]styryl]-4H-pyran (a DCM derivative) by the palladium-catalyzed Suzuki coupling reaction. The copolymers were characterized by molecular weight determination, elemental analysis, 1H NMR, FT-IR spectroscopy, DSC, TGA, UV−vis spectroscopy, and photoluminescence (PL) and electroluminescence (EL) spectroscopy. The copolymers showed two absorption peaks at 380 and 485 nm, and the long-wavelength absorption increased with increasing the fraction of the DCM comonomer. The PL spectra of copolymers in chloroform solution displayed emission from both the main chain (420 nm) and DCM units (620 nm). In the solid state, however, PL spectra of copolymers showed only ...

Highly ordered nanostructures of liquid-crystal molecules were patterned within porous anodic alumina of different pore diameters. As the utilized pore diameter of the porous membrane decreases, progressively red-shifted emissions are observed for the embedded liquid-crystal nanostructures at room temperature. This unique spectral progression, depending on the pore size, is very similar to the emission trend induced by the thermotropic phase-transitions of the bulk antiferroelectric liquid-crystal. Such characteristics are considered to be due to structural confinement of the antiferroelectric liquid-crystal molecules within the finite size of nanoporous channels.

133 Cs ( I =7/2) nuclear magnetic resonance in a Cs 2 CoCl 4 single crystal grown by using the slow evaporation method was measured in the two mutually perpendicular crystal planes. The 133 Cs resonances of two different groups, respectively, with two crystallographically inequivalent cesium nuclei, Cs(I) and Cs(II) in the unit cell, were recorded. From their angular dependences, the Cs(I) and the Cs(II) nuclei have different values for the quadrupole coupling constant and the asymmetry parameter. The quadrupole coupling constant and the asymmetry parameter obtained for Cs(I) with a smaller separation were e 2 q Q / h =725 kHz and η=0.58. Those for Cs(II) with a larger separation were e 2 q Q / h =802 kHz and η=0.85. The electric field gradient (EFG) tensors of Cs(I) and Cs(II) are asymmetric, and the orientations of their principal axes do not coincide. The Cs(I) ion surrounded by 11 chlorine ions has a small quadrupole parameter and is high in symmetry. The Cs(II) ion surrounded by 9 chlorine ions has a...

Diarylethene copolymers were synthesized from 1-(6 0 -vinyl-2 0 -methylbenzo[b]thiophene-3 0 -yl)-2-(2 00 -methylbenzo[b]thiophene-3 00 -yl)hexafluorocyclopentene (VMBTF6) and 1-[6 0 -(4 000 -vinylbenzoyl)-2 0 -methylbenzo[b]thiophene-3 0 -yl]-2(2 00 -methylbenzo[b]thiophene-3 00 -yl)hexafluorocyclopentene (VBMBTF6) via living free radical techniques using stable TEMPO derivatives. The diarylethene content was controlled by the feed ratio of diarylethene derivatives and styrene. Transparent photochromic polymer films were prepared from the diarylethene copolymers with narrow molecular weight dispersion (PD � 1:3) by spin coating method. Photoinduced refractive index changes (DnTE) of the polymer films, with 25 mol% of diaryethene content, accompanied by the photochromic change were determined as 0.0009 and 0.0030 for poly(styrene-ran-VMBTF6) and poly(styrene-ran-VBMBTF6), respectively. 2002 Published by Elsevier Science B.V.

Pheophorbide-a derivatives have been reported to be potential photosensitizers for photodynamic therapy (PDT). In this study, photophysics of pheophorbide-a derivatives (PaDs) were investigated along with their photodynamic tumoricidal effectin vitro. PaDs were modified by changing the coil length and/or making the hydroxyl group (–OH) substitutions. Their photophysical properties were studied by steady-state and time-resolved spectroscopic methods. The photodynamic tumoricidal effect was evaluated in the mouse breast cancer cell line (EMT6). Lifetime and quantum yield of fluorescence and quantum yields of triplet state and singlet oxygen were studied to determine the dynamic energy flow. The coil length of the substituted alkyl group did not significantly affect the spectroscopic properties. However, the substitution with the hydroxyl group increased the quantum yields of the triplet state and the singlet oxygen due to the enhanced intersystem crossing. In order to check the application possibility as a photodynamic therapy agent, the PaDs with hydroxyl group were studied for the cellular affinity and the photodynamic tumoricidal effect of EMT6. The results showed that the cellular affinity and the photodynamic tumoricidal effect of PaDs with the hydroxyl group depended on the coil-length of the substituted alkyl group.

Xerographic photoconductivity of 3,5-dinitrobenzoates of poly[1-(p-methoxyphenyl)penta-1,3-diyn-5-ol], poly[1-(2'-methoxyphenyl)penta-1,3-diyn-5-ol] and poly[1-(p-N,N-dimethylaminophenyl)penta-1,3-diyn-5-ol] [DN-1,2-PMDO, DN-1,4-PMDO and DN-1,4-PDDO] is dependent on the electron donating side chains. From the transient photoconductivity signal on a sub-nanosecond time scale, a plausible mechanism for the charge carrier generation and charge transporting properties of these polymers is proposed.

Photochromic reactions of three diarylethene derivatives embedded in three types of polymer matrices were studied using a variety of spectroscopic techniques and quantum ab initio computations. It was found that the photochromic efficiencies of diarylethene molecules depend on the structural and electronic characteristics of Franck–Condon region in the excited states, and also depend strongly on the sizes of free inner spaces of the matrices. The steady-state and time-resolved fluorescence studies revealed the detailed kinetics of the planar and twisted conformers in the excited states. The observed fluorescence lifetimes of the planar and twisted conformers were ∼2.6 ns and 8∼30 ns.

Nuclear spin-lattice relaxations of Be9 and Al27 in an alexandrite (BeAl2−xCrxO4, x=0.02) single crystal have been investigated in the temperature range 140 K–400 K. The paramagnetic impurity effect on the relaxation is negligible for both nuclei. The relaxation of the Be9 nuclear spins is found single exponential in time when the whole resonance lines are uniformly excited. When only the central resonance line is excited for Al27, the relaxation is well fitted with a linear combination of three exponential functions given by Simmons et al. [Phys. Rev. 127, 1168 (1962)]. Since the spin-lattice relaxation rate is proportional to the square of temperature for both nuclei, the dominant relaxation mechanism in this temperature range can be inferred as the Raman process.

Organic photovoltaic devices are difficult to commercialize because of their vulnerability to chemical degradation related with oxygen and water and to physical degradation with aging at high temperatures. We investigated the photophysical degradation behaviors of a series of poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl C61-butyric acid methyl ester (PC60BM) bulk heterojunctions (BHJs) as a model system according to the donor–acceptor ratio. We found that the optimum P3HT:PC60BM ratio in terms of long-term stability differs from that in terms of initial cell efficiency. On the basis of cell performance decays and time-resolved photoluminescence measurements, we investigated the effects of oxygen and material self-aggregation on the stability of an organic photovoltaic device. We also observed the changes in morphological geometry and analyzed the surface elements to verify the mechanisms of degradation.

The reported photocurrent density (J SC) of PbS quantum dot (QD)-sensitized solar cell was less than 19 mA/cm2 despite the capability to generate 38 mA/cm2, which results from inefficient electron injection and fast charge recombination. Here, we report on a PbS:Hg QD-sensitized solar cell with an unprecedentedly high J SC of 30 mA/cm2. By Hg 2+ doping into PbS, J SC is almost doubled with improved stability. Femtosecond transient study confirms that the improved J SC is due to enhanced electron injection and suppressed charge recombination. EXAFS reveals that Pb-S bond is reinforced and structural disorder is reduced by interstitially incorporated Hg2+, which is responsible for the enhanced electron injection, suppressed recombination and stability. Thanks to the extremely high J SC, power conversion efficiency of 5.6% is demonstrated at one sun illumination. Refereed/Peer-reviewed

Unique starlike CdS particles were prepared from the lyotropic triblock copolymer solution system. The starlike CdS consists of a spherical core and dozens of the attached conical nanolobes. From the comparative studies with the spherical and rod-shaped CdS nanoparticles, the unique photophysical property is presented for the starlike CdS particle. The experimental results suggest that the photogenerated charge carriers at the tip-edge region of the conical nanolobe in the starlike CdS system diffuse into the thicker inner part including the core region, which is possibly due to the decreasing excited state potential gradient from the tip edge to the thicker inner part. This type of charge carrier diffusion dynamics from the surrounding to the thicker inner part in this anisotropic morphology of the starlike CdS semiconductor closely resembles the energy transfer dynamics in the organic dendrimers.

The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(π,π(*)) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(π,π(*)) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(π,π(*)) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(π,π(*)) excited state.

We report the original fabrication and performance of a photocurrent device that uses directly grown CdSe quantum dots (QDs) on a graphene basal plane. The direct junction between the QDs and graphene and the high quality of the graphene grown by chemical vapor deposition enables highly efficient electron transfer from the QDs to the graphene. Therefore, the hybrids show large photocurrent effects with a fast response time and shortened photoluminescence (PL) lifetime. The PL lifetime quenching can be explained as being due to the efficient electron transfer as evidenced by femtosecond transient absorption spectroscopy. These hybrids are expected to find applications in flexible electronics and optoelectronic devices.

Proton conducting solids are of potential interest for fuel cells, steam electrolysis, and as sensors. Proton conduction occurs in several types of materials including many hydrogen-bonded systems. In some ferroelectric and ferroelastic hydrogen-bonded crystals the superionic conductivity was discovered: MHSO4 (M = K, Rb, Cs, NH4) exhibit high proton conductivity in their high temperature phases. The hydrogen sulfate family, MHSO4 has received much attention owing to its interesting properties. The most interesting group in the crystal structures of this series is the HSO4 ion, which is usually distorted and arranged, in a tetrahedral symmetry. Potassium hydrogen sulfate, KHSO4, is a member of the alkali acid sulfate family interesting because of its ferroelectric behavior. Until now, the phase transition temperature in the KHSO4 crystal has not been exactly established. The structure of a KHSO4 single crystal is orthorhombic with space group Pbca (D 2h) and with sixteen molecules per unit cell. The unit cell parameters are a 1⁄4 8:4030 A, b 1⁄4 9:799 A, and c 1⁄4 18:945 A. All the 16 Kþ and 16 HSO 4 ions in the unit cell occupy sites of C1 symmetry. There are two types of crystallographically different Kþ, as well as HSO 4 , ions in the cell. According to the crystal structure data, one kind of HSO 4 ion appears to form a chain of similar units whereas two units of the other kind of HSO 4 ion occupy positions at opposite sides of a point of inversion, forming a dimer through two intermolecular H-bonds. Recently, we reported on the K nuclear magnetic resonance (NMR) at room temperature. The EFG tensors of K(1) and K(2) were asymmetric and the orientations of the principal axes of the EFG tensors did not coincide for the K(1) and K(2) sites. These results show that the K(1) and the K(2) sites, which are surrounded by nine oxygen atoms, were clearly distinguished by K NMR. KHSO4 crystals have previously been studied by means of X-ray diffraction, electron paramagnetic resonance and Raman scattering measurements. In order to obtain information about the dynamic motions of the HSO4 ion, it is necessary to measure the spin–lattice relaxation times, T1, of H and K in KHSO4 single crystals. However, very few NMR studies relating to the dynamic motion of the oxygen atoms have been reported. In this paper, the temperature dependences of the spin– lattice relaxation time, T1, for the H and the K nuclei in a KHSO4 single crystal grown by using the slow evaporation method were investigated using a pulse NMR spectrometer. The relaxation times of the H and the K nuclei in a KHSO4 single crystal are new observations. Single crystals of KHSO4 were grown at room temperature by using slow evaporation of an aqueous solution containing a stoichiomeric proportion of K2SO4 and H2SO4. The crystals with hexagonal shapes were colorless and transparent and had good optical quality. The NMR signals of H and K in the KHSO4 crystal were measured using the Bruker MSL 200 FT NMR and the Bruker DSX 400 FT NMR spectrometers, respectively, at the Korea Basic Science Institute. The H spin–lattice relaxation time was measured in the temperature range from 140K to 400K at a frequency of 200MHz. The spin–lattice relaxation time, T1, was measured by applying a pulse sequence of 180 –t–90 . The nuclear magnetization SðtÞ of H at time t after the 180 pulse was determined from the inversion recovery sequence following the pulse. The recovery traces of the magnetization of the crystals were measured at several different temperatures. The recovery traces of H show a single exponential function. The temperature dependence of T1 for H in the single crystal is shown in Fig. 1. In the case of the H nucleus, the spin–lattice relaxation time is long with T1 1⁄4 382 s at room temperature. The variation of the relaxation rate, T 1 1 , with temperature exhibits a minimum. As the temperature is increased, the H relaxation rate slowly decreases, and then begins to increase, passing through a minimum at 210K. The curve of T 1 1 in this temperature range has a positive parabolic shape with a minimum near 210K. This result is not consistent with the trend of H in the hydrogen sulfate family: the shape of T 1 1 for H has a positive parabolic shape in KHSO4 while the plots of T 1 1 for H in RbHSO4 and NH4HSO4 crystals 17,18) have a negative parabolic shape. Therefore, by the Bloembergen–Purcell–Pound (BPP) theory, the change in the slope of T1 for H in KHSO4 at about 210K is not believed to be related to HSO4 motion. The trend of H in KHSO4 crystals is not usual. In order to check the phase transition temperature, we measured differential scanning calorimetry (DSC) using a Du Pont 2010 DSC instrument measurements. From this result, KHSO4 showed four phase transitions in the temperature range from 140K to 473K: 451, 453, 456, and 462K.

We have demonstrated the lasing in the porous alumina membrane filled with hybrid polymer nanowires which consisted of poly(N-vinylcarvazole), rhodamine 6G, and TiO2 nanoparticles. The angle-resolved photoluminescence measurement suggested that lasing had a strong directionality along the hybrid polymer nanowires which were embedded within the nanochannels of the membrane. Although wavelengths of the lasing peaks were not affected by excitation and detection angles, lasing behavior strongly depended on the pore diameters of the membranes utilized. It is suggested that the closed loops for lasing are formed via multiple scattering induced by TiO2 nanoparticles embedded in the hybrid polymer nanowires.

Hollow microporous organic networks bearing isocoumarin moieties (H-IC-MONs) were prepared via a tandem synthetic approach. Pd catalysts conducted the networking of building blocks by the Sonogashira coupling with the concomitant generation of isocoumarins through cyclization. The H-IC-MONs showed visible light absorption and emission properties and were applied to nitrophenol sensing using visible light.