Guanidinium-Pseudohalide Perovskite Interfaces Enable Surface Reconstruction of Colloidal Quantum Dots for Efficient and Stable Photovoltaics.

Complete surface passivation of colloidal quantum dots (CQDs) and their strong electronic coupling are key factors toward high-performance CQD-based photovoltaics (CQDPVs). Also, the CQD matrices must be protected from oxidative environments, such as ambient air and moisture, to guarantee air-stable operation of the CQDPVs. Herein, we devise a complementary and effective approach to reconstruct the oxidized CQD surface using guanidinium and pseudohalide.

Solvent Engineering of Colloidal Quantum Dot Inks for Scalable Fabrication of Photovoltaics.

Development of colloidal quantum dot (CQD) inks enables single-step spin-coating of compact CQD films of appropriate thickness, enabling the promising performance of CQD photovoltaics (CQDPVs). Today's highest-performing CQD inks rely on volatile -butylamine (BTA), but it is incompatible with scalable deposition methods since a rapid solvent evaporation results in irregular film thickness with an uneven surface. Here, we present a hybrid solvent system, consisting of BTA and ,-dimethylformamide, which has a favorable acidity for colloidal stability as well as an appropriate vapor pressure, enabling a stable CQD ink that can be used to fabricate homogeneous, large-area CQD films via spray-coating.

Hybrid Surface Passivation for Retrieving Charge Collection Efficiency of Colloidal Quantum Dot Photovoltaics.

Efficient charge collection in photovoltaics is a key issue toward their high performance. Despite the promising performance of colloidal quantum dot (CQD)-based photovoltaics (CQDPVs), they suffer significant dissipation of photocurrent due to imperfect surface passivation of the CQD hole transport layer (HTL) by a single 1,2-ethaneditihol (EDT) ligand. To address the critical drawback of existing CQDPVs, we offer a hybrid passivation strategy, including both EDT and thiocyanate (SCN).

Improving Charge Collection from Colloidal Quantum Dot Photovoltaics by Single-Walled Carbon Nanotube Incorporation.

Improving charge collection is one of the key issues for high-performance PbS colloidal quantum dot photovoltaics (CQDPVs) due to the considerable charge loss resulting from the low mobility and large defect densities of the 1,2-ethanedithiol-treated PbS quantum dot hole-transporting layer (HTL). To overcome these limitations, single-walled carbon nanotubes (SWNTs) and C-encapsulated SWNTs (C@SWNTs) are incorporated into the HTL in CQDPVs. SWNT-incorporated CQDPV demonstrates a significantly improved short-circuit current density (), and C@SWNT-incorporated CQDPV exhibits an even higher than that of pristine SWNT.

Electric Property Change of Single-Walled Carbon Nanotube by the Encapsulation of Aliphatic Thiols.

The encapsulation of single-walled carbon nanotubes (SWNTs) with aliphatic thiol compounds with a relatively small amount of ionization energy achieves -type doping of SWNTs. Thiol compounds encapsulated inside nanotubes in vacuum drastically change the electric properties of SWNTs by a charge transfer between the two species. The simplicity of the synthetic process offers a viable route for large-scale production of SWNTs with controlled doping states by using mat-type SWNTs.

Vibrational Spectrocopic Studies of Organic Molecules After Encapsulation Inside Single-Walled Carbon Nanotubes.

7,7,8,8-tetracyano-p-quinodimethane (TCNQ), tetrathiafulvalene (TTF), and dodecanethiol (DoSH) were encapsulated inside single-walled carbon nanotubes (SWNTs), (TCNQ@SWNT, TTF@SWNT, and DoSH@SWNT). We measured the Fourier transform infra-red (FTIR) spectra and X-ray diffraction (XRD) patterns to confirm the encapsulation of organic molecules. Slight shifts of the FTIR peaks and the disappearance of an XRD peak at ~6°, corresponding to the SWNT (10) reflection, were observed.

A Study of the Wettability of Single-Walled Carbon Nanotube Films on Flat and Textured Si Substrates.

Contact angle measurements are investigated on the surface of single-walled carbon nanotube (SWNT) films directly formed on flat and textured Si substrates using a thermal chemical vapor deposition method. The SWNT films on the textured Si consist of a multiscale structure composed of nanoscale SWNTs and a microscale textured Si. They show superhydrophobic properties in which the water contact angle was around 161°.

Improved Field Emission of Three-Dimensional Single-Walled Carbon Nanotube Networks Suspended Between ZnO Nanorods.

We report field emission (FE) properties of three dimensional single-walled carbon nanotube (3-D SWNT) networks synthesized between ZnO nanorods on textured Si wafer. The FE properties are measured for turn-on field and field enhancement factor, and are compared with other types of SWNT films such as synthesized SWNT films and spray SWNT films. 3-D SWNT has lower turn-on field and higher field enhancement factor than other SWNT films.

Conductivity Properties of Single-Walled Carbon Nanotubes Upon the Encapsulation of TTF and TCNQ.

N-type and p-type single-walled carbon nanotubes (SWNTs) were formed via the encapsulation of tetrathiafulvalene (TTF) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) inside SWNTs, respectively. Raman, near-infrared, and X-ray photoelectron spectrometer were used to confirm the encapsulation. From measurements of the current-voltage curves in a vacuum, it was revealed that current of TTF-encapsulated SWNTs decreased and TCNQ-encapsulated SWNTs increased comparing with that of pristine SWNTs.

Suppressed Interfacial Charge Recombination of PbS Quantum Dot Photovoltaics by Graphene Incorporated into ZnO Nanoparticles.

Single-layer graphene (SLG) was incorporated into ZnO nanoparticles (NPs), and use of this material in photovoltaic devices generated significant changes. The Fermi level of ZnO NPs underwent a downshift, whereas the conduction and valence bands were maintained with increasing SLG concentrations. Furthermore, the effective defect densities were reduced and carrier mobility was enhanced.

Photocurrent Enhancement of CdSe Quantum-Dot Sensitized Solar Cells Incorporating Single-Walled Carbon Nanotubes.

We demonstrate quantum-dot sensitized solar cells (QDSSCs) which have colloidal CdSe quantum dots (TOPO-CdSe) as a sensitizer onto mesoporous TiO2 photoanodes. CdS quantum-dot (QD) layer plays a role of buffer layer for direct adsorption of TOPO-CdSe. We incorporate single-walled carbon nanotubes with TiO2 photoanode of our QDSSCs to facilitate efficient charge transfer.

Field Emission and Electrical Properties of Perovskite.

We investigate characteristic field emission properties of methyl ammonium mixed-halide perovskite (CH3NH3PbI3-xClx) and their current change under one laser pulse. To analyze these properties, we fabricated inverted-type mixed-halide perovskite solar cells which exhibit a device efficiency of 9.31% under A.

Selective Growth of Metallic and Semiconducting Single Walled Carbon Nanotubes on Textured Silicon.

We fabricated the etched Si substrate having the pyramidal pattern size from 0.5 to 4.2 μm by changing the texturing process parameters, i.

Performance Enhancement of 3-Mercaptopropionic Acid-Capped CdSe Quantum-Dot Sensitized Solar Cells Incorporating Single-Walled Carbon Nanotubes.

We fabricated a series of linker-assisted quantum-dot-sensitized solar cells based on the ex situ self-assembly of CdSe quantum dots (QDs) onto TiO2 electrode using sulfide/polysulfide (S(2-)/Sn(2-)) as an electrolyte and Au cathode. Our cell were combined with single-walled carbon nanotubes (SWNTs) by two techniques; One was mixing SWNTs with TiO2 electrode and the other was spraying SWNTs onto Au electrode. Absorption spectra were used to confirm the adsorption of QDs onto TiO2 electrode.

Structure and Hydrogen Adsorption Properties of SBA-15 Doped with Pd Nanoparticles.

Hydrogen adsorption properties of Pd-doped Santa Barbara amorphous No. 15 (Pd-SBA-15) were investigated and the results were compared with pure SBA-15 ones in terms of change of its structure and Pd concentration. Pd-SBA-15 samples were prepared by a hydrothermal reaction, using mixture of PEO20PPO70PEO20 (P123) and tetraethyl orthosilicate (TEOS).

Enhancement of Photo-Current Conversion Efficiency in a CdS/CdSe Quantum-Dot-Sensitized Solar Cell Incorporated with Single-Walled Carbon Nanotubes.

Cadmium sulfide (CdS) and cadmium selenide (CdSe) are sequentially assembled onto a nanocrystalline TiO2 film to create a quantum-dot (QD)-sensitized solar cell application by a successive ionic layer adsorption and reaction (SILAR) method. The results show that CdS and CdSe QDs have a complementary effect in the performance of light harvest of solar cell. Single-walled carbon nanotubes (SWNTs) are incorporated with a CdS/CdSe QDs solar cell by mixing them with TiC2 film to enhance electron transfer.

Field emission properties of a three-dimensional network of single-walled carbon nanotubes inside pores of porous silicon.

We report characteristic field emission (FE) properties of single-walled carbon nanotubes (SWCNTs) synthesized inside the pores as well as on the top surface of a porous silicon (PS) substrate. Turn-on fields and emission current densities were measured and compared with those of other types of SWCNTs in similar environments. Investigation of the FE properties of SWCNTs synthesized inside the pores of a PS substrate revealed a low turn-on field of approximately 2.

Measurement of contact resistance in CdSe-single-walled carbon nanotube hybrids.

The CdSe-single-walled carbon nanotube (SWNT) hybrids are synthesized for measuring contact resistance between CdSe quantum dots and SWNTs in two hybrid samples, i.e., spray-deposited CdSe on SWNTs, and pyrene-self assembled CdSe on SWNTs.

Current flow of single-walled carbon nanotubes upon the encapsulation of beta-carotene by using conducting probe atomic force microscopy.

Beta-carotene was inserted into single-walled carbon nanotubes (SWCNTs) by using the encapsulation method in a solution phase, and the energy transfer process was studied under irradiation of visible light. The encapsulation of beta-carotene inside SWCNTs was confirmed by ultraviolet (UV)/visible (Vis) and near-IR (N-IR) spectroscopy, and the stability of encapsulated beta-carotene was also confirmed by a UV irradiation experiment. The N-IR absorption spectrum revealed that the beta-carotene donated electrons to the SWCNTs upon encapsulation.

Formation of ZnO nanostructures grown on Si and SiO2 substrates.

ZnO nanorods are grown on Si-based substrate by chemical bath deposition method in aqueous solution using zinc nitrate hexahydrate. Various substrates having different surface morphology are used to evaluate their effect on growing ZnO nanorods, such as flat Si(100) wafer, small and large textured-Si wafer, porous silicon, flat SiO2 wafer, small and large textured-SiO2 wafer. The length, diameter, geometry, and coverage density of ZnO nanorods are investigated by field-emission scanning electron microscopy and summarized.

Electron transfer properties of iodine-doped single-walled carbon nanotubes using field effect transistor.

Single-walled carbon nanotubes (SWNTs) are known to have a p-type charge transfer character in the atmosphere. The energy state of SWNTs can be modulated by doping with either an electron donor or an acceptor. In this study, iodine molecules are chosen for intercalation to SWNTs to predict the charge transfer tendency between them.

Photoluminescence study of encapsulated dye inside single-walled carbon nanotubes dispersed in solvents.

Photo-luminescent dye, 1-(2-amino-phenyl) naphthalene-2-ylamine (APNA) molecules were synthesized and encapsulated inside single-walled carbon nanotubes (APNA@SWNTs) in vacuum. Here we measured X-ray diffraction (XRD) pattern and attenuated total reflectance (ATR) spectrum to confirm the encapsulation of APNA molecules inside SWNTs. Strong photoluminescence (PL) spectrum was observed around 400 nm at an excitation of 326 nm.

Large scale synthesis and enhanced field emission properties from hybrid CuO/ZnO nanorod.

Upper-directionally grown nanorods were synthesized on a large scale by a simple method of direct heating of Cu foil in air. Hybrid CuO/ZnO nanorods were fabricated by ZnO thin film coating using magnetron sputtering. Field emission (FE) measurements of CuO and hybrid CuO/ZnO nanorod films show that they have turn-on field of 3.

The spin population difference of hydrogen atoms dissociated from mercury hydride molecules.

The spin population difference between m(s) = 1/2 and - 1/2, (malpha - mbeta)(t) of the hydrogen atoms dissociated from the mercury hydride molecules is calculated as a function of time for the reaction of Hg* + H2 in a magnetic field. Starting from zero value, the population difference increases to a certain limit that is equal to the room temperature population difference. The H/D electron spin resonance (ESR) signal ratio obtained from the isotopic experiment, Hg* + H2/D2, is also explained by comparing the ratio of (malpha - mbeta)H(t) and (malpha - mbeta)D(t).