Chun-hsien Chen

Enhanced Performance and Air Stability of 3.2% Hybrid Solar Cells: How the Functional Polymer and CdTe Nanostructure Boost the Solar Cell Efficiency

A record high PCE of up to 3.2% demonstrates that the efficiency of hybrid solar cells (HSCs) can be boosted by utilizing a unique mono-aniline end group of PSBTBT-NH(2) as a strong anchor to attach to CdTe nanocrystal surfaces and by simultaneously exploiting benzene-1,3-dithiol solvent-vapor annealing to improve the charge separation at the donor/acceptor interface, which leads to efficient charge transportation in the HSCs.

Acid/Base‐ and Anion‐Controllable Organogels Formed From a Urea‐Based Molecular Switch

Low-molecular-weight organogels have applications in several fields, including molecular sensing, nanostructure assembly, and drug delivery. Ideally, these materials would switch reversibly between their solution and gel states through the addition or removal of heat, electrons, or ions. Although these modes of operation are similar to those employed for switches based on interlocked molecules, organogels formed from pseudorotaxaneor rotaxane-type gelators are rare. Indeed, we are aware of only a few previously reported examples, all of which feature long alkyl chains or cholesterol units incorporated into the molecular structures to assist the gelation process. Predicting the molecular structures of potential gelators and their preferred solvents remains difficult, and developing new rotaxane-based gelators that do not feature commonly used types of gelation units (e.g., long alkyl chains, steroids) in their structures is particularly challenging. Herein we report the serendipitous discovery of a urea-based [2]rotaxane that behaves as both a molecular switch and an organogelator; both functions are mediated by acid/base and anion control. The reaction of the macrocycle 1, the amino-terminated salt [2-H][PF6], [7] and the isocyanate 3 in CH3NO2 gave the dumbbell-shaped salt [4-H][PF6] and the [2]rotaxane [5-H][PF6] in 49 and 46% yield, respectively (Scheme 1). The binding constant for the assembly formed from the macrocycle 1 and dibenzylammonium hexafluorophosphate ((DBA)PF6) in CD3NO2 is (300 30)m , and 1 interacts only negligibly with diphenylurea derivatives in this solvent. 8] Therefore we suspected that the interlocked macrocycle in the [2]rotaxane [5-H][PF6] would prefer to encircle the DBA station, rather than the diphenylurea station, when dissolved in CD3NO2. Indeed, the 2D NOESY spectrum of the [2]rotaxane [5-H][PF6] in CD3NO2 shows cross-signals between the ethylene glycol protons of the macrocyclic unit and the aromatic protons of the 3,5-di-tert-butylphenyl stopper adjacent to the DBA center, however, no crosssignals are seen between the macrocyle and the stopper unit adjacent to the urea station. As expected, addition of potassium tert-butoxide (1 equivalent) to a solution of the [2]rotaxane [5-H][PF6] (CD3NO2, 13.6 mm) resulted in significant shifts in the locations of many of the signals in the H NMR spectrum (Figure 1). The significant downfield shift of the signal for the macrocyle NH protons, and the appearance of signals for the formerly severely broadened urea protons suggested the formation of hydrogen bonds to the carbonyl group of the urea station (Figure 1b). The addition of perchloric acid (70% in H2O, 1 equivalent) to this solution afforded a spectrum similar to that of the original [2]rotaxane. These observations suggest that the [2]rotaxane [5-H][X] is an acid/base-controllable molecular switch; the interlocked macrocyclic unit can be Scheme 1. Synthesis and switching of the [2]rotaxane [5-H][PF6].

Superior Contact for Single-Molecule Conductance: Electronic Coupling of Thiolate and Isothiocyanate on Pt, Pd, and Au

One of the critical issues for the realization of molecular electronics is the development of ideal molecule-electrode contacts that render efficient charge transportation and thus attenuate the unwanted voltage drop and power loss. The conductance at the single-molecule level has long been expected to be correlated strongly with the electrode materials. However, other than gold, systematic studies of a homologous series of molecules to extract the headgroup-metal contact conductance (G(n=0)) have not been reported. Carefully examined herein are the conductances of alkanedithiols anchored onto electrode materials of Au and Pt as well as the conductances of alkanediisothiocyanates on Au, Pd, and Pt by utilizing the method of STM-BJ (scanning tunneling microscopy break junction). In comparison with Au substrate, Pd and Pt are group 10 elements with stronger d-orbital characteristics, and larger local density of states near the Fermi level. The model compounds, SCN(CH(2))(n)NCS (n = 4, 6, and 8), are studied because the isothiocyanate (-NCS) headgroup is a versatile ligand for organometallics, an emerging class of molecular wires, and can bind to substrates of noble metals to complete a metal-molecule-metal configuration for external I-V measurements. Also studied include alkanedithiols, one of the most scrutinized systems in the field of single-molecule conductance. The results show that the conductance for single molecules bridged between a pair of Pt electrodes is about 3.5-fold superior to those between Au electrodes. On all electrode materials, observed are two sets of conductance values, with the smaller set being 1 order of magnitude less conductive. These findings are ascribed to the degree of electronic coupling between the headgroup and the electrode.

Extended Metal-Atom Chains with an Inert Second Row Transition Metal : [Ru5(μ5-tpda)4X2] (tpda2-= tripyridyldiamido dianion, X = Cl and NCS)

EMACs (extended metal-atom chains) offer a unique platform for the exploration of metal-metal interactions. There has been significant advances on the synthesis of EMACs, such as lengthening the chains up to 11 metal atoms thus far, integrating naphthyridine moieties for tuning the charge carried at metal centers, and manipulation of metal-metal interactions. However, the metal centers in EMACs hitherto are limited to first row transition metals which are more labile than those relatively inert ones with electrons filled in the 4d and 5d shells. In this Communication, the synthesis, crystallographic, magnetic, and electrical conducting studies of [Ru5(mu5-tpda)4Cl2] and [Ru5(mu5-tpda)4(NCS)2], the first pentanuclear EMACs of second-row transition metal, are reported.

Steric Zipper of the Amyloid Fibrils Formed by Residues 109–122 of the Syrian Hamster Prion Protein

We report the results of atomic force microscopy, Fourier-transform infrared spectroscopy, solid-state nuclear magnetic resonance, and molecular dynamics (MD) calculations for amyloid fibrils formed by residues 109-122 of the Syrian hamster prion protein (H1). Our data reveal that H1 fibrils contain no more than two beta-sheet layers. The peptide strands of H1 fibrils are antiparallel with the A117 residues aligned to form a linear chain in the direction of the fibril axis. The molecular structure of the H1 fibrils, which adopts the motif of steric zipper, is highly uniform in the region of the palindrome sequence AGAAAAGA. The closest distance between the two adjacent beta-sheet layers is found to be about 5 A. The structural features of the molecular model of H1 fibrils obtained by MD simulations are consistent with the experimental results. Overall, our solid-state NMR and MD simulation data indicate that a steric zipper, which was first observed in the crystals of fibril-forming peptides, can be formed in H1 fibrils near the region of the palindrome sequence.

Superiority of Branched Side Chains in Spontaneous Nanowire Formation: Exemplified by Poly(3-2-methylbutylthiophene) for High-Performance Solar Cells

One-dimensional nanostructures containing heterojunctions by conjugated polymers, such as nanowires, are expected to greatly facilitate efficient charge transfer in bulk-heterojunction (BHJ) solar cells. Thus, a combined theoretical and experimental approach is pursued to explore spontaneous nanowire formation. A dissipative particle dynamics simulation is first performed to study the morphologies formed by rodlike polymers with various side-chain structures. The results surprisingly predict that conjugated polymers with branched side chains are well suited to form thermodynamically stable nanowires. Proof of this concept is provided via the design and synthesis of a branched polymer of regioregular poly(3-2-methylbutylthiophene) (P3MBT), which successfully demonstrates highly dense nanowire formation free from any stringent conditions and stratagies. In BHJ solar cells fabricated using a blend of P3MBT and [6,6]-phenyl-C71-butyric acid methyl ester (PC(71) BM), P3MBT polymers are self-organized into highly crystalline nanowires with a d(100) spacing of 13.30 Å. The hole mobility of the P3MBT:PC(71) BM (1:0.5 by weight) blend film reaches 3.83 × 10(-4) cm(2) V(-1) s(-1) , and the maximum incident photon-to-current efficiency reaches 68%. The results unambiguously prove the spontaneous formation of nanowires using solution-processable conjugated polymers with branched alkyl side chains in BHJ solar cells.

Coadsorption of sulfate anions and silver adatoms on the Au(111) single crystal electrode. Ex situ and in situ comparison

Abstract Interactions of sulfate anions in diluted sulfuric acid solutions with the Ag Au(111) surface were studied using Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), Atomic Force Microscopy (AFM), Core Electron Energy Loss Spectroscopy (CEELS) and electrochemistry. At electrode potentials more positive than those within the silver deposition range sulfate adsorbate forms an ordered Au(111)(√3 × √3)R30 ° adlattice, and gives rise to a corresponding, but diffuse, LEED pattern. Following extensive rinsing procedure, silver forms two well-ordered structures, Au(111)p(3 × 3) and Au(111)p(5 × 5). However, AFM images reveal a clear p(3 × 3)-4Ag structure, which condenses to a close packed p(1 × 1)-Ag overlayer at more negative potentials. Distinctive S(LMM) Auger electron transitions and the S(L2,3) core electron energy loss of the sulfate adsorbate show a characteristic S6+ sulfur valency, giving evidence that the sulfur oxidation state is not altered in the ultra-high vacuum environment following solution/vacuum transfer.

Colorimetric Sensitivity of Gold Nanoparticles: Minimizing Interparticular Repulsion as a General Approach

GNPs (gold nanoparticles) as an eye-catching sensor rely on the high extinction coefficients and the shift of the surface plasmon band which signals the disperse-to-aggregate transformation. The selectivity of the sensors is dictated by the surface functionality whose density presumably has a positive correlation with the sensitivity toward the targeted analyte. To improve the analytical performance, most efforts in this research field focus on the design and synthesis of the sensing elements as well as on the increase in density on GNPs. Proposed here is an alternative rationale that the further improvement of the GNP sensitivity can be achieved by minimizing the electrostatic repulsion and hence the energy barrier for the recognition event to take place. Our model system begins with thioctic acid-stabilized GNPs which are subsequently modified with 15-crown-5 ether for the recognition toward K (+). For a given coverage of 15-crown-5 ether, the limits of detection (LODs) can be improved by more than 3 orders of magnitude via adjusting the solution pH and ionic strength which we suggest a general guideline for the optimization of a new GNP sensing scheme. Following this guideline, satisfactory performance with LODs at the micromolar level can be systematically and efficiently found for GNPs with a range of 15-crown-5 ether coverage.

On the tuning of electric conductance of extended metal atom chains via axial ligands for [Ru3(μ3-dpa)4(X)2]0/+ (X = NCS−, CN−)

The influence of a pi-acid cyanide axial ligand on the metal-metal interactions of [Ru(3)(mu(3)-dpa)(4)(X)(2)](0/+) (X = NCS(-), CN(-)) is manifested by the measurements of single-molecule conductance coupled with in situ electrochemical control.

Shear-Induced Long-Range Uniaxial Assembly of Polyaromatic Monolayers at Molecular Resolution

The control of spatial arrangements of molecular building blocks on surfaces opens the foundational step of the bottom-up approach toward future nanotechnologies. Contemporarily, the domain size of monolayers exhibiting crystallinity falls in the submicrometer scale. Developed herein is a method that allows the alignment of polyaromatics with one-single domain for as long as 7 mm. Even more exciting is the fact that the method is applicable to every laboratory and costs practically nothing. The monolayers are prepared simply by placing a piece of folded lens paper against the substrate and the deposition solution containing the compound of interest. The preparation scheme is similar to the Couette flow where the laminar flow takes place between two concentric walls, one of which rotates and creates viscous drag proven useful to align macromolecules. The method can induce an edge-on orientation for 3,6,11,14-tetradodecyloxydibenzo[g,p]chrysene (DBC-OC12), 3,6,12,15-tetrakis(dodecyloxy)tetrabenz[a,c,h,j]anthracene (TBA-OC12), and hexakis(4-dodecyl)-peri-hexabenzocoronene (HBC-C12) and unsubstituted coronene which would otherwise adopt the face-on arrangement on graphite. This finding will be useful to the research and industry that demands high quality alignment of polyaromatics such as OTFTs, optical polarizers, and nanodevices associated with molecular self-assembly.