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Perovskite solar cell is a thin-film cell made from solution process including coating, sintering, crystallization, and then encapsulated to become a solar cell that can generate electricity at low cost. At present, the power conversion efficiency of laboratory-produced small cell (

Detecting and discriminating chemical vapors are essential for environmental monitoring and medical diagnostics. In this study, highly sensitive chemical vapor sensors fabricated from fluorinated t...

Anionic and cationic defects are considered as one of the crucial factors that affect carrier transport property and degradation of perovskite photovoltaic materials. Herein, we demonstrate a simpl...

Using a novel ultraviolet (UV) irradiation method, we processed a high-performance thin-film transistor (TFT) at low temperatures. Satisfactory device integrity that was demonstrated by high field-effect mobility values of 92 and 43 cm2/Vs, small subthreshold slopes of 74 and 81 mV/decade, and ON-current/ OFF-current values of $3\times 10^{6}$ and $7\times 10^{5}$ was achieved for the SnO2 TFT at low processing temperatures of 180 °C and 100 °C, respectively. The results of X-ray photoelectron spectroscopy showed that the UV irradiation considerably increased the presence of Sn4+ and reduced the presence of unwanted Sn2+, even at low processing temperatures, improving the quality of SnO2.

Oligo(ethylene glycol) (OEG) side chains are widely used in donor-acceptor conjugated polymers (D-A CPs) and enable the polymers to dissolve and be processed in environmentally friendly and cost-effective nonchlorinated solvents, such as water. However, the OEG effect on the physical properties of D-A CPs has not been thoroughly studied and sometimes the results are controversial. In this study, two oligothiophene-isoindigo based conjugated polymers, P3TI and P4TI, are selected as model polymers to investigate the OEG effect. PnTI has octyl side chains on the oligothiophene unit and 2-hexyldecyl side chains on the isoindigo unit. The replacement of an alkyl side chain with OEG not only changes the optical and thermal properties but also the molecular arrangements of the polymers such as π-π d-spacing, crystallinity, and packing orientation. The domination of the crystallization behavior changes from the oligothiophene unit to the isoindigo unit when the bulky alkyl group is replaced by the flexible and linear OEG. The packing changes from edge-on to face-on orientation. The results are intriguing and provide new insights into this class of polymers.

Nanostructures in conducting polymer films can enhance charge carrier and ion transfer, provide porosity with high specific area and confer unique optoelectronic properties for potential applications. A general and facile synthesis has been developed to prepare nanostructured conducting polymer films without the need for using templates. This simple approach employs hyperbranched polymers as additives to tune the morphology of conducting polymer films into a continuous nanofibril network. Nanostructured conducting polymer films with improved crystallinity exhibit good charge carrier transport and stable nanofibril network, without sacrificing either property upon removing residual additives. Polymer field-effect transistor sensors have been used to demonstrate the benefits of the large surface area provided by the nanofibril network. The sensors with porous nanostructures exhibit lower detection limits (two times lower) and faster response times (33% faster) compared to the sensors without nanostructures. This general approach can advance the knowledge and development of nanostructured conducting polymer films for energy harvesting and storage, electronics, catalysts, sensors and biomedical applications.

Sol–gel metal oxide films are an important type of functional materials for energy technologies and beyond owing to their versatile properties and ease of processing, but their applications are limited by the typically required high sintering temperatures. This study reports a novel phenomenon where the sintering temperatures of sol–gel metal oxide films were substantially lowered when a metal phase was embedded within the sol–gel precursor films. Morphological and compositional analyses revealed that the reduction in sintering temperatures was enabled by a mechanism similar to the metal-induced crystallization (MIC) process, with a distinction that catalysis of sol–gel reactions occurred alongside the induction of crystallization. We observed this catalytic MIC (c-MIC) mechanism in a variety of sol–gel material systems including NixO with embedded Au or Ag; TiOx with embedded Ni, Au, or Pt; and SnOx with embedded Ni. Based upon this concept, we demonstrated highly efficient flexible and rigid organic/inorganic hybrid perovskite solar cells (PSCs) using a low-temperature-sintered NixO film embedded with Au nanoislands as the hole-transporting layer (HTL). The c-MIC mechanism reduced the sintering temperature of the Au-embedded NixO HTL by 100 °C, making the NixO process compatible with plastic substrates while allowing the NixO HTL to retain more NiOOH surface groups, which enhanced hole collection and improved the quality of the perovskite layer. Thanks to the advantages of the c-MIC NixO film, the flexible and rigid PSCs achieved high power conversion efficiencies of up to 15.9 and 19.0%, respectively, which were sustained for >1200 h at 65 °C and 65% relative humidity. Our findings provide a practical route for low-temperature fabrication of high-quality oxide functional films by solution-based sol–gel processes, which will be valuable to a wide variety of applications in addition to thin film solar cells.

Bulk heterojunction (BHJ) perovskite solar cells have recently attracted increased interest because of a significantly enhanced interface between perovskite and the n-type material in the active layer for efficient charge separation and increased power conversion efficiency (PCE). [6,6]-Phenyl-C61-butyric acid methyl ester (PC61BM) is the most commonly used n-type material in BHJ perovskite solar cells owing to its high electron mobility. However, it is very difficult to fabricate BHJ perovskite films because of the poor solubility of PC61BM in the commonly used solvent dimethylformamide (DMF). In this study, we introduced two kinds of fluorinated PC61BM (3F-PC61BM and 5F-PC61BM) as n-type materials in a BHJ perovskite film, which have higher solubility in DMF than that of PC61BM. Thus, a BHJ perovskite film can be easily fabricated in one step using a single solvent in a BHJ precursor solution system for planar perovskite solar cells. A BHJ device with a high PCE of 16.17% can be obtained by adding 0.1 wt% of 3F-PC61BM in a perovskite precursor solution to fabricate a solar cell, which outperforms the PCE of 14.12% of the pristine device. However, the addition of 5F-PC61BM decreased the PCE to lower than that of the pristine device regardless of its amount. We systematically studied the effects of the amount and type of fluorinated PC61BM on the morphology of BHJ perovskite films using SEM, AFM, GISAXS and GIWAXS. The results reveal that 3F-PC61BM can fill the pinholes between perovskite grains and passivate the defects in the pristine film. Thus, the current density (Jsc) is greatly increased. On the other hand, the self-aggregation of 5F-PC61BM in BHJ perovskite films caused the films to be full of large voids, which led to poor device performance. The dense and flat surface morphology of BHJ perovskite films containing 3F-PC61BM can also prevent the permeation of moisture into grain boundaries and enhance the device stability. Therefore, the device could maintain 80% of its original efficiency over 550 hours without any encapsulation in comparison with 240 hours for the pristine device. Our results provide a novel strategy for fabricating high-PCE and high-stability BHJ perovskite solar cells for the production of low-cost solar cells in the near future.

Organic–inorganic lead halide perovskite solar cells are considered as one of the most promising technologies for future photovoltaics because they show high power conversion efficiency (PCE) and can be fabricated through a simple solution process. Non-toxic alkaline-earth metal cations are suitable candidates to replace toxic lead in perovskite because they maintain the charge balance in perovskite and some of them meet the tolerance factor of Goldschmidt's rule. We investigated four kinds of alkaline-earth metal cations (Mg2+, Ca2+, Sr2+, and Ba2+) to replace lead cations partially. Among these four alkaline-earth metals, the Ba2+ is most suitable for Pb2+ replacement in perovskite films and exhibits the best power conversion efficiency. Furthermore, we systematically studied the crystal structure, absorption behavior and surface morphology of Ba2+-doped perovskite films with different doping levels. The relationship between the charge carrier dynamics and Ba2+ concentration was evaluated by the time-resolved photoluminescence (TRPL) technique. The Ba2+-doped perovskite films that can be processed in the environment containing moisture (1.0% relative humidity) are stable. At the optimal 3.0 mol% Ba2+ replacement, the PCE of the fabricated solar cell is increased from 11.8 to 14.0%, and the PCE of champion devices is as high as 14.9% with increased storage stability.

Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3NH3PbI3–xClx perovskite in cross-sectional geometry. Two electronic phases, 10–20 nm in size, with different electronic properties inside the CH3NH3PbI3–xClx perovskite layer are observed by the dI/dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. By comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at −2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).

Controlling the crystallization and morphology of perovskite films is crucial for the fabrication of high-efficiency perovskite solar cells. For the first time, we investigate the formation mechanism of the drop-cast perovskite film from its precursor solution, PbCl2 and CH3NH3I in N,N-dimethylformamide, to a crystalline CH3NH3PbI3–xClx film at different substrate temperatures from 70 to 180 °C in ambient air and humidity. We employed an in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) technique for this study. When the substrate temperature is at or below 100 °C, the perovskite film is formed in three stages: the initial solution stage, transition-to-solid film stage, and transformation stage from intermediates into a crystalline perovskite film. In each stage, the multiple routes for phase transformations are preceded concurrently. However, when the substrate temperature is increased from 100 to 180 °C, the formation mechanism of the perovskite film is changed from the “multistage formatio...

Perovskite solar cells (PSCs) have earned widespread attention owing to its fast-growing power conversion efficiency (PCE). However, there are some challenges for this type of solar cells. The toxicity issue, current density-voltage (J-V) hysteresis, and uncertain stability hinder commercialization. In this study, we developed the PSCs with MA0.4FA0.6BaxPb1-xIyCl3-y film as active layer. The MA0.4FA0.6BaxPb1-xIyCl3-y film with various barium doping concentrations were fabricated by solvent engineering method. We investigate the surface morphology, crystal orientation, and optical property of various perovskite films. Furthermore, the in situ grazing-incidence wide-angle X-ray scattering (in-situ GIWAXS) is used to analyze the heating crystallization process of perovskite film. We discover that Ba can improve crystallinity and structural stability. For the optimal 5.0 mol% Ba replacement, the PCE of perovskite device is increased to 17.4%, the J-V hysteresis can be completely eliminated and the device demonstrates long-term stability.

Here we demonstrated an approach to increase performance of P3HT:TiO 2 solar cell either by electron deficient boron or electron rich bismuth doping into TiO 2 nanorods. The B doping increases the absorption, crystallinity and electron mobility of TiO 2 nanorods. The Bi-doped TiO 2 has higher J sc as compared with B-doped TiO 2 , mainly due to the improvement of electron density and increased absorption of TiO 2 nanorods. The devices were fabricated from TiO 2 nanorods being surface modified by organic dye W-4. The dye facilitates the bandgap alignment and compatibility between TiO 2 and P3HT. The power conversion efficiency of solar cell has been increased by 1.33 times and 1.30 times for Bi-doped TiO 2 and B-doped TiO 2 , respectively, as compared with that of as-synthesized TiO 2 . The results suggest the optical and electronic properties of TiO 2 can be tuned by various dopants to enhance the device performance.

A hierarchical pore network in planar CH3NH3PbI3 perovskite is demonstrated herein. Quantitative characterizations by grazing incidence small angle X-ray scattering (GISAXS) with modeling and complementary microscopic observations provide insight at various length scales. It is a pore structure comprised of nano-scaled primary pores aggregating into meso-scaled fractal networks within the perovskite layer. Its structural evolution and mechanistic interpretation are explored with respect to different preparation methods/steps. The time-of-flight secondary ion mass spectrometer (TOF-SIMS) results suggest the infiltration of hole transporting materials (HTM) or electron transporting materials (ETM) deposited on top at different length scales. The inter-penetrating perovskite/HTM or perovskite/ETM form i–p or i–n one-sided porous heterojunctions, respectively, over the typically regarded planar-stacked heterojunction. They show distinctive photovoltaic characteristics and behaviors in which the large i–n interfaces at the nanoscale lead to highly efficient, hysteresis-free and reliable solar cell devices. The morphology–performance correlation is helpful for associated design of device architecture and processing toward higher efficiency and stability.

In this work, we demonstrate the solution processing of optical and electrochemical dye sensors based on 4-(dioctylamino)-4′-(trifluoroacetyl)azobenzene and its application in sensing different amine compounds. Distinct optical response of the sensors exposed to ammonia, tetramethylammonium hydroxide, ethylamine, cadaverine and putrescine (typical compounds upon the decomposition of proteins) is observed. Incorporation of inkjet deposited thin films of the dye as sensors in food packages of ground meat and salmon is found as a feasible route to detect the appearance of biogenic amines produced by the degrading food products. Furthermore, we demonstrate an electrochemical amine sensor based on (trifluoroacetyl)azobenzene dye added in carbon nanotube–Nafion® composites. The electrochemical sensor exploits the reaction between the dye and amines to detect amines in electrolytes, while the carbon nanotubes provide large surface for adsorption and also provide a percolating electrical network for allowing efficient charge transfer at the electrode electrolyte interface.

The high power conversion efficiency of bulk heterojunction (BHJ) polymer solar cells can be achieved from either low crystallinity (P3TI) or high crystallinity (P6TI) of isoindigo-based donor–acceptor alternating copolymers blended with PC71BM by controlling nanophase separation using additives. P3TI shows similar device performance regardless of the type of additives, while P6TI is significantly affected by whether the additive is aliphatic or aromatic. To understand the interplays of crystallinity of polymers and the type of additive on the formation of nanomorphology of BHJ, we employed the simultaneous grazing-incidence small- and wide-angle X-ray scattering (GISAXS and GIWAXS) technique to perform the quantitative investigation. By incorporating additives, the PC71BM molecules can be easily intercalated into the P3TI polymer-rich domain and the size of the PC71BM clusters is reduced from about 24 nm to about 5 nm by either aliphatic 1,8-diiodooctane (DIO) or aromatic 1-chloronaphthalene (CN). On comparison, it is found to be more difficult for PC71BM molecules to be intercalated into the highly crystalline P6TI dense domain, and the PC71BM molecules have a higher tendency to be self-aggregated, which results in a larger size of PC71BM clusters of about 58 nm. The clusters can be reduced to about 7 nm by DIO and 13 nm by CN. The presence of crystallites in the P6TI domain can interact with the additive to tailor the crystallization of PC71BM clusters to a size similar to that of P6TI crystallites (∼12 nm) and form a connected network for efficient charge transportation. Thus, the power conversion efficiency of P6TI:PC71BM reaches its maximum of 7.04% using aromatic CN additives. This is a new finding of the effect of crystallinity, which is not observed in the common low crystalline donor–acceptor alternating copolymers such as PTB7. Our results provide a useful guideline to manipulate the desired morphology of BHJ films constructed from alternating copolymer with different crystallinity, which is critical for achieving high power conversion efficiency of solar cells.

High performance p-type thin-film transistor (p-TFT) was realized by a simple process of reactive sputtering from a tin (Sn) target under oxygen ambient, where remarkably high field-effect mobility (μ FE ) of 7.6 cm2/Vs, 140 mV/dec subthreshold slope, and 3 × 104 on-current/off-current were measured. In sharp contrast, the SnO formed by direct sputtering from a SnO target showed much degraded μ FE , because of the limited low process temperature of SnO and sputtering damage. From the first principle quantum-mechanical calculation, the high hole μ FE of SnO p-TFT is due to its considerably unique merit of the small effective mass and single hole band without the heavy hole band. The high performance p-TFTs are the enabling technology for future ultra-low-power complementary-logic circuits on display and three-dimensional brain-mimicking integrated circuits.

In this paper, the use of hot solvent vapor (HSV) annealing is demonstrated to improve the performance of polymer solar cells (PSCs) fabricated by the spray process. The blend of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM) is used as a photoactive layer of the solar cell. Compared to the conventional solvent vapor annealing, the HSV annealing can eliminate the formation of intra-droplet boundary during the spray process and optimize the nanostructure of the film quickly (≤5 min). The study of conducting atomic force microscopy (C-AFM) reveals that the HSV annealed film exhibits smooth film surface and homogenous conductivity distribution. Moreover, an enhanced light harvesting and increased crystallinity of P3HT in the active layer are observed by UV–vis absorption and X-ray diffraction (XRD). With subsequent thermal annealing, the power conversion efficiency of solar cell made from the HSV annealed film is reached at 3.61%. This HSV annealing technique can be implemented into the fabrication of high efficient large-area PSCs using the spray process.

Colloid TiO(2) nanorods are used for solution-processable poly(3-hexyl thiophene): TiO(2) hybrid solar cell. The nanorods were covered by insulating ligand of oleic acid (OA) after sol-gel synthesis. Three more conducting pyridine type ligands: pyridine, 2,6-lutidine (Lut) and 4-tert-butylpyridine (tBP) were investigated respectively to replace OA. The power conversion efficiency (PCE) of the solar cell was increased because the electronic mobility of pyridine-type ligand-modified TiO(2) is higher than that of TiO(2)-OA. The enhancement of PCE is in the descending order of Lut > pyridine > tBP because of the effective replacement of OA by Lut. The PCE of solar cell can be further enhanced by ligand exchange of pyridine type ligand with conjugating molecule of 2-cyano-3-(5-(7-(thiophen-2-yl)-benzothiadiazol-4-yl) thiophen-2-yl) acrylic acid (W4) on TiO(2) nanorods because W4 has aligned bandgap with P3HT and TiO(2) to facilitate charge separation and transport. The electronic mobility of two-stage ligand exchanged TiO(2) is improved furthermore except Lut, because it adheres well and difficult to be replaced by W4. The amount of W4 on TiO(2)-tBP is 3 times more than that of TiO(2)-Lut (0.20 mol % vs. 0.06 mol %). Thus, the increased extent of PCE of solar cell is in the decreasing order of tBP > pyridine > Lut. The TiO(2)-tBP-W4 device has the best performance with 1.4 and 2.6 times more than TiO(2)-pyridine-W4 and TiO(2)-Lut-W4 devices, respectively. The pKa of the pyridine derivatives plays the major role to determine the ease of ligand exchange on TiO(2) which is the key factor mandating the PCE of P3HT:TiO(2) hybrid solar cell. The results of this study provide new insights of the significance of acid-base reaction on the TiO(2) surface for TiO(2)-based solar cells. The obtained knowledge can be extended to other hybrid solar cell systems.

Organic–inorganic hybrid bulk heterojunction (BHJ) solar cells have attracted much attention due to their low cost fabrication, flexibility, and long life. However, the compatibility between organic and inorganic materials is still an issue that needs to be solved to achieve high power conversion efficiency (PCE). The larger size and dense characteristics of inorganic nanocrystals make it hard to control the morphology and phase separation of organic–inorganic hybrid thin films by conventional processes like thermal annealing and solvent annealing. In this study, we have carried out a systematic investigation using an additive: rod–coil diblock copolymer poly(3-hexyl thiophene)-b-poly(2-vinyl pyridine) (P3HT-b-P2VP) to P3HT:TiO2 to make a ternary system. That improves the compatibility between the P3HT homopolymer and the TiO2 nanorod hybrid materials and results in enhanced performance of the hybrid solar cell. The hydrophobic characteristics of the P3HT segment of the copolymer are compatible with the P3HT homopolymer, and the P2VP segment, containing a pyridine moiety is more compatible with hydrophilic TiO2. The results of atomic force microscopy and X-ray diffraction spectroscopy studies of hybrid films reveal that the crystallization behavior of the homopolymer P3HT in the film can be tuned by incorporating different weight ratios of P3HT-b-P2VP. The efficiency of charge separation is also improved as observed by greater photoluminescence quenching. Furthermore, the power conversion efficiency of the solar cell fabricated from this new hybrid system was increased threefold as compared with the one without the additive (1.20% vs. 0.42%), which indicates that the amphiphilic P3HT-b-P2VP can effectively modulate the interfacial interactions between the conducting polymer and nanocrystals in both solution and film to have the appropriate morphology for high efficient solar cells.

Very high mobility of 149∼189 cm2/Vs, large on-to-off current ratio (I ON /I Off ) of >7 orders of magnitude, fast turn-on sub-threshold swing of 110 mV/decade, and low power operation at 2∼2.5 V were achieved in SnO 2 TFT device at an ultra-thin SnO 2 thickness of 4.5 nm. The device mobility of SnO 2 TFT is higher than the best ZnO-based TFTs and CVD-grown multi-layers MoS 2 MOSFETs. The reached mobility is already 0.7 times of universal mobility of SiO 2 /Si nMOSFET, operated typically at >1 MV/cm field. The very high mobility, simple low temperature process, and ultra-thin body SnO 2 transistor should find its crucial role for high resolution display, future sub-10 nm nMOSFET and brain-mimicking 3D IC.

High mobility channel thin-film-transistor (TFT) is crucial for both display and future generation integrated circuit. We report a new metal-oxide TFT that has an ultra-thin 4.5 nm SnO2 thickness for both active channel and source-drain regions, very high 147 cm2/Vs field-effect mobility, high ION/IOFF of 2.3 × 107, small 110 mV/dec sub-threshold slope and a low VD of 2.5 V for low power operation. This mobility is already better than chemical-vapor-deposition grown multi-layers MoS2 TFT. From first principle quantum-mechanical calculation, the high mobility TFT is due to strongly overlapped orbitals.

The aim of this study is to quantitatively investigate the effect of different fullerene type (PC60BM and PC70BM) on various morphological structures and power conversion efficiency (PCE) in the bulk heterojunction (BHJ) P3HT/PCxBM solar cells. The solar cells are fabricated by spin coating without thermal annealing. The quantitative investigations of three-dimensional self- organized nanostructures are performed by using combined grazing- incidence small- and wide-angle X-ray scattering technique (GISAXS/GIWAXS). Two types of nanostructures are observed due to the phase separation in the BHJ films during the processing. They include (1) intercalated PCxBM molecules around boundary of P3HT crystalline domain and within amorphous domain and (2) aggregated PCxBM clusters in PCxBM domains. The lamellar spacing of P3HT crystalline domains in P3HT/PC70BM is larger than that in P3HT/PC60BM. This result indicates more interfacial areas are generated between PC70BM and P3HT at the molecular scale for more efficient charge separation. On the other hand, the size, volume fraction, partial attachment, and spatial distribution of PC60BM clusters are larger than that of PC70BM clusters, which reveals more efficient electron transport in P3HT/PC60BM. We deduce the correlation between nanostructures and PCE (3.25% and 2.64%, respectively, for P3HT/ PC70BM and P3HT/PC60BM). The structure of fullerene intercalated with P3HT rather than the size of fullerene cluster plays a major role in the PCE performance of BHJ solar cell without thermal annealing.

We have developed multi-walled carbon nanotube/liquid crystalline epoxy composites and studied the effects of incorporation carbon nanotubes (CNTs) on the morphology, thermal and mechanical properties of the composites. The CNTs are functionalized by liquid crystalline (LC) 4,4′-bis(2,3-epoxypropoxy) biphenyl (BP) epoxy resin for the ease of dispersion and the formation of long range ordered structure. The epoxy functionalized CNT (ef-CNT) were dispersed in the LC BP epoxy resin that can be thermal cured with an equivalent of 4,4′-diamino-diphenylsulfone to form composite. The curing process was monitored by polarized optical microscopy. The results indicate the LC resin was aligned along the CNTs to form fiber with dendritic structure initially then further on to obtain micro-sized spherical crystalline along with fibrous crystalline. With homogeneous dispersion and strong interaction between nanotubes and matrix, the composite containing 2.00 wt.% ef-CNT exhibits excellent thermal and mechanical properties. When the amount of ef-CNT exceeds 2.00 wt.%, vitrification stage of curing is fast reached, which lowers the degree of conversion. As compared with the neat resin, the composite containing 2.00 wt.% ef-CNT increases the glass transition temperature by 70.0 °C, the decomposition temperature by 13.8 °C, the storage modulus by 40.9%, and the microhardness by 63.3%.

Both the performance and stability are the two major tasks for scientists to tackle in polymer solar cells. We introduce 3-hydroxyflavone (3-HF), a free-radical scavenging agent, as an additive in poly(3-hexythiophene):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM) blend forming new photoactive material, which is used as an active layer in inverted solar cell devices. It was found that the addition of an adequate amount of 3-HF enhances the photocurrent, which is due to the improved carrier mobility. A power conversion efficiency (PCE) of the device has improved from 2.57% to 3.05%. In addition, 3-HF can further stabilize the inverted solar cell performance with a 85% retaining of its original PCE over a month in ambient condition as compared to the additive-free device of a value of 57%. Thus, incorporating 3-HF as an additive is an effective and simple method to approach the goal of high PCE while maintaining stable ambient operation.

Low-temperature thermal chemical vapor deposition (thermal CVD) synthesis of multi-walled carbon nanotubes (MWCNTs) was studied using a large variety of different precursor compounds. Cyclopentene oxide, tetrahydrofuran, methanol, and xylene: methanol mixture as oxygen containing heteroatomic precursors, while xylene and acetylene as conventional hydrocarbon feedstocks were applied in the experiments. The catalytic activity of Co, Fe, Ni, and their bi-as well as tri-metallic combinations were tested for the reactions. Low-temperature CNT growth occurred at 400 degrees C when using bi-metallic Co-Fe and tri-metallic Ni-Co-Fe catalyst (on alumina) and methanol or acetylene as precursors. In the case of monometallic catalyst nanoparticles, only Co (both on alumina and on silica) was found to be active in the low temperature growth (below 500 degrees C) from oxygenates such as cyclopentene oxide and methanol. The structure and composition of the achieved MWCNTs products were studied by scanning and transmission electron microscopy (SEM and TEM) as well as by Raman and X-ray photoelectron spectroscopy (XPS) and by X-ray diffraction (XRD). The successful MWCNT growth below 500 degrees C is promising from the point of view of integrating MWCNT materials into existing IC fabrication technologies. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The selection of carrier transporting layer in polymer solar cells is an important issue because the nature and direction of carrier transport can be manipulated by inserting different functional layers in the device structure. In this work, we report a very efficient inverted polymer solar cell (PSC) system based on regioregular poly(3-hexylthiophene) and a n-type acceptor, bis-indene[C60]. With a pair of metal oxides and the insertion of TiO2 nanorods electron collecting layer between the ZnO thin film and the active layer, the device efficiency can be greatly improved. The contact area between the active layer and the electron collecting layer, as well as the thickness of active layer, can be increased with the incorporation of TiO2 nanorods. As a result, photocurrent can be enhanced due to more absorption of light and more charge separation interface. In addition, the larger contact area and the crystalline TiO2 nanorods provide a more efficient transporting route for the carriers to the cathode. The most efficient device demonstrated shows a high power conversion efficiency of 5.6% with the inverted structure.

The external quantum efficiencies of P3HT:PCBM blend solar cells decrease significantly when they are bent or illuminated at large incident angles because of (i) optical anisotropy of the P3HT:PCBM films—primarily because a mismatch between the direction of the electric field of the incoming light and the orientation of the P3HT:PCBM blend nanocrystallites results in a significant reduction in the amount of TM-polarized light absorbed and (ii) interfacial reflection of multilayer structures – primarily because the outermost air–flexible substrate interface exhibits a distinct refractive index difference – at large incident angles. Textured moth-eye structures fabricated by nanoimprint lithography on the flexible substrates of organic solar cells reduce the degree of interfacial reflection at high incident angles; they should allow more TE-polarized light to absorb in the P3HT:PCBM films (active layers) of the organic solar cells.

We report the synthesis of N-doped TiO(2) nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol-water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N-Ti bonds appear in the lattice, resulting in slight lattice expansion as shown by XPS and HR-TEM analysis, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination. When 100 mg of catalyst (N-doped TiO(2) nanofiber decorated with Pt nanoparticles) was applied to 1 L of water-ethanol mixture, the H(2) evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h (UV-B) corresponding to photo energy conversion percentages of ∼3.6 and ∼12.3%, respectively.

A new class of nanocomposite has been fabricated from liquid crystalline (LC) epoxy resin of 4,4′-bis(2,3-epoxypropoxy) biphenyl (BP), 4,4′-diamino-diphenyl sulfone (DDS), and multiwalled carbon nanotubes (CNTs). The surface of the CNTs was functionalized by LC epoxy resin (ef-CNT). The ef-CNT can be blended well with the BP that is further cured with an equivalent of DDS to form nanocomposite. We have studied the curing kinetics of this nanocomposite using isothermal and nonisothermal differential scanning calorimetry (DSC). The dependence of the conversion on time can fit into the autocatalytic model before the vitrification, and then it becomes diffusion control process. The reaction rate increases and the activation energy decreases with increasing concentration of the ef-CNT. At 10 wt % of ef-CNT, the activation energy of nanocomposite curing is lowered by about 20% when compared with the neat BP/DDS resin. If the ef-CNT was replaced by thermal-insulating TiO2 nanorods on the same weight basis, the decrease of activation energy was not observed. The result indicates the accelerating effect on the nanocomposite was raised from the high-thermal conductivity of CNT and aligned LC epoxy resin. However, at ef-CNT concentration higher than 2 wt %, the accelerating effect of ef-CNTs also antedates the vitrification and turns the reaction to diffusion control driven. As the molecular motions are limited, the degree of cure is lowered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

In this paper, we present two different types of polymer/metal oxide nanocrystals hybrid photovoltaics. One is the poly(3-hexylthiophene) (P3HT)/TiO2 nanorods hybrid bulk heterojunction (BHJ) solar cell and the other is a nanostructured ZnO/P3HT hybrid solar cell. In a BHJ hybrid solar cell, the dispersed semiconducting nanocrystals lead to an increased interface area between polymer and nanocrystals, which can assist charge separation for photogenerated carriers, but at the expense of poorly formed conducting pathways for electron transport. In contrast, a nanostructured hybrid solar cell usually consists of rigidly connected nanocrystals, which can provide direct pathways for electron transport, but the interface area between polymer and nanocrystals is limited. We have demonstrated that through interface modification with effective molecules, the photovoltaic performance in both device structures can be largely improved by enhancing charge separation and suppressing interface recombination rate in the polymer/inorganic hybrids.

We conducted an extensive study on poly(3-hexylthiophene) (P3HT) in combination with titanium dioxide (TiO 2 ) nanorods hybrid material for polymer solar cell applications. The device performance critically depends on the morphology of the hybrid film that will be determined by the molecular weight of P3HT, the solvent type, the hybrid compositions, the surface ligand on the TiO 2 nanorods, film thickness, process conditions, and so on. The current–voltage characteristic of the device fabricated in air has shown a power conversion efficiency of 0.83% under air mass (AM) 1.5 illumination using high molecular weight (65,000 D) P3HT, high boiling point solvent trichlorobenzene, and pyridine-modified TiO 2 nanorods with a film thickness of about 100 nm. The Kelvin probe force microscopy (KPFM) study of hybrid films shows large-scale phase separation with domain size greater than 10 nm, which may be the main factor limiting device performance.

We have studied the effect of polymer molecular weight on the performance of poly(3-hexylthiophene):TiO2 hybrid photovoltaic device using atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM). The atomic force microscopic studies show the nanoscale morphology of the hybrid film changes from small domain size rod-like structure to large domain nodule-like structure with increasing the molecular weight of poly(3-hexylthiophene). The studies of SNOM of hybrid film reveal that the large domain structure of the high-molecular-weight P3HT hybrid film exhibits continuous absorption mapping as opposite to the discontinuous absorption mapping of the low-molecular-weight P3HT hybrid film. Both results suggest the improvement in device efficiency from high-molecular-weight P3HT is due to the formation of large domain structure with increased carrier mobility and light harvesting.

We have investigated the enhancement of light absorption and carrier transport of poly(3-hexylthiophene) (P3HT) resulted from doping with multi-wall carbon nanotubes (MWNTs). The MWNTs were acid washed first, and then incorporated into P3HT homogenously. The MWNTs make P3HT unfolded with more alignment and thus increase light absorption as shown by the studies of AFM and UV–vis spectroscopy. The KFM data provides useful information to differentiate the work function of the MWNTs from P3HT and further show improved hole transporting behaviors. Based upon these results, the 0.01 wt% MWNTs doped P3HT/PCBM photovoltaic device shows an increase of 29% power conversion efficiency.

A highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) film was prepared by in-situ oxidative polymerization on a glass substrate and adopted as the transparent anode of polymer solar cells that were based on a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) as the photoactive layer. PEDOT anodes of various thicknesses were prepared for use in such devices. The resistance of the PEDOT and the transmitted light intensity of the irradiation varied with the thickness. The best devices exhibited a power conversion efficiency of 2.6% under simulated AM1.5G solar irradiation. Importantly, the conversion efficiency of incident photons to electrons in the device with the PEDOT anode was comparable to that with an ITO electrode, indicating the practicability of applying PEDOT as anode to fabricate high-efficiency flexible solar cells.

Recently, head-to-tail regioregular poly(3-hexylthiophene) (P3HT) has been widely used as an active material in fabricating polymer optoelectronic devices. This study employs UV-vis absorption, photoluminescence (PL), X-ray diffraction (XRD) and the space-charge limited current (SCLC) model to elucidate the effect of light illumination on the optic and optoelectronic properties of P3HT. The degraded performance of P3HT, such as low absorbance, PL emission, and charge-carrier mobility is caused mostly by a reduction in the degree of conjugated structure and the lower crystallinity.

We have investigated systematically the differences of silver cofirability and microwave dielectric properties between Zn3Nb2O8 and Bi1.5Zn0.92Nb1.5O6.92 (BZN). Two type dopants: 0.29BaCO3–0.71CuO (BC) and 0.81MoO3–0.19CuO (MC) were used in Zn3Nb2O8 and Bi1.5Zn0.92Nb1.5O6.92 ceramics so they can be cofired with silver. The BC-doped ceramics in general have better dielectric properties than those of MC-doped ceramics. The BC-doped Zn3Nb2O8 exhibits better dielectric properties than those of BC-doped BZN (k = 14.7, Q × f = 8200 GHz versus k = 120.1, Q × f = 1050 GHz). For silver compatibility study, the interfacial behaviors between microwave dielectric materials and silver were investigated by using X-ray diffractometer, scanning electronic microscope, and electronic probe microanalyzer. No new crystalline phase and no silver migration behavior were found in the BC-doped Zn3Nb2O8 ceramics cofired with silver, but slight silver migration was detected for BC-doped BZN. But slight silver migration was detected for MC-doped Zn3Nb2O8 and BZN ceramics cofired with silver. Therefore, the good overall properties of BC-doped Zn3Nb2O8 are suitable for microwave applications.

Zn3Nb2O8 has been considered as candidate microwave materials due to its high quality factor. However, Zn3Nb2O8 has to be sintered above 1200 °C. We have lowered Zn3Nb2O8 sintering temperature to 950 °C by using 3 wt.% of BC additives (0.29BaCO3–0.71CuO). The doped Zn3Nb2O8 exhibits good microwave properties at 8.3 GHz (k = 14.7, Q × f = 8200 GHz). The interfacial behavior between Zn3Nb2O8 dielectric and silver was investigated by using X-ray diffractometer, scanning electronic microscope, and electronic probe microanalyzer. No new crystalline phase and no silver migration behavior were found after cofiring doped Zn3Nb2O8 and silver electrode at 950 °C for 4 h. The low sintering temperature BC doped Zn3Nb2O8 with high Q × f value has a potential for microwave applications.

Two-dimensional (2D) arrays of gold nanoparticles with sulfur-containing fullerene nanoparticles were self-assembled through the formation of Au−S covalent bonds. Disulfide functional groups were introduced into the C60 molecule by reacting propyl 2-aminoethyl disulfide with C60. The 2D arrays were formed at the interface of the aqueous phase of gold particles and organic phase of fullerene particles as a blue transparent film. Transmission electronic microscope images showed that the fullerene spacing between adjacent Au (∼10 nm) particles was about 2.1 ± 0.4 nm, which was consistent with the result of 2.18 nm by molecular molding calculations (MM+). The UV−visible spectrum of this film showed a red shift and increased bandwidth due to the small spacing between gold nanoparticles. The arrays were deposited on the top of pairs of gold electrodes to form 2D colloidal single electron devices. The electrode pairs were made by electron beam lithographic techniques, and the separation between tips of the two e...

We grew and processed a blue/green two-wavelength light-emitting diode (LED) based on the mixture of two kinds of quantum wells (QW) in epitaxial growth. The X-ray diffraction and photoluminescence measurements indicated that the crystalline structure and the basic optical property of individual kinds of QW are not significantly changed in the mixed growth. The relative electroluminescence (EL) intensity of the two colors depends on the injection current level, which controls the hole concentration distribution among the QWs. At low injection levels, the top green-emitting QW dominates in EL. As the injection current increases, the blue-emitting QWs beneath become dominating. We also coated CdSe-ZnS nanocrystals on the top of the two-wavelength LED for converting blue photons into red light. With the coating of such nanocrystals, the device emits blue, green, and red lights for white light generation

Blue-red polychromatic light-emitting devices are fabricated by attaching red-emitting CdSe-ZnS nano-crystals on a blue-emitting InGaN-GaN multiple-quantum-well (MQW) structure. To improve the red/blue intensity contrast, holes of different diameters are fabricated for increasing the direct contact area between the MQW active regions and CdSe-ZnS nano-crystals. By comparing the devices of 10-, 50-, 60-, and 70-mum hole diameters, and a reference device of no hole, it is found that the hole diameter of 60 mum represents an optimized condition from the viewpoint of maintaining high quantum efficiency. However, the device of 10-mum holes has the highest red/blue intensity ratio, which corresponds to a 36% increase. This result is attributed to its largest side-wall area in the holes among various samples

We demonstrate here that the nanostructure of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM) bulk heterojunction (BHJ) can be tuned by inorganic nanoparticles (INPs) for enhanced solar cell performance. The self-organized nanostructural evolution of P3HT/PCBM/INPs thin films was investigated by using simultaneous grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence wide-angle X-ray scattering (GIWAXS) technique. Including INPs into P3HT/PCBM leads to (1) diffusion of PCBM molecules into aggregated PCBM clusters and (2) formation of interpenetrating networks that contain INPs which interact with amorphous P3HT polymer chains that are intercalated with PCBM molecules. Both of the nanostructures provide efficient pathways for free electron transport. The distinctive INP-tuned nanostructures are thermally stable and exhibit significantly enhanced electron mobility, external quantum efficiency, and photovoltaic device performance. These gains over conventional P3HT/PCBM directly result from newly demonstrated nanostructure. This work provides an attractive strategy for manipulating the phase-separated BHJ layers and also increases insight into nanostructural evolution when INPs are incorporated into BHJs.

In this study, single-electron transistors and memory cells with Au colloidal islands linked by C60 derivatives have been fabricated by hybridization of top–down advanced electron-beam lithography and bottom–up nanophased-material synthesis techniques. Low-temperature transport measurements exhibit clear Coulomb-blockade-type current–voltage characteristics and hysteretic-type gate-modulated current. The hysteresis is attributed to the presence of electrically isolated charge–storage islands. With the guidance provided by Monte Carlo simulation, we propose a circuit model and give an estimate of the sample parameters.

We have developed an improved small-angle X-ray scattering (SAXS) model and analysis methodology to quantitatively evaluate the nanostructures of a blend system. This method has been applied to resolve the various structures of self-organized poly(3-hexylthiophene)/C61-butyric acid methyl ester (P3HT/PCBM) thin active layer in a solar cell from the studies of both grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence X-ray diffraction (GIXRD). Tuning the various length scales of PCBM-related structures by a different annealing process can provide a flexible approach and better understanding to enhance the power conversion of the P3HT/PCBM solar cell. The quantitative structural characterization by this method includes (1) the mean size, volume fraction, and size distribution of aggregated PCBM clusters, (2) the specific interface area between PCBM and P3HT, (3) the local cluster agglomeration, and (4) the correlation length of the PCBM molecular network within the P3HT phase. The above terms are correlated well with the device performance. The various structural evolutions and transformations (growth and dissolution) between PCBM and P3HT with the variation of annealing history are demonstrated here. This work established a useful SAXS approach to present insight into the modeling of the morphology of P3HT/PCBM film. In situ GISAXS measurements were also conducted to provide informative details of thermal behavior and temporal evolution of PCBM-related structures during phase separation. The results of this investigation significantly extend the current knowledge of the relationship of bulk heterojunction morphology to device performance.

In this article, the polymer photovoltaic devices based on the poly(3-hexylthiophene) /TiO 2 nanorods hybrid material is present. An enhancement in the device performance can be achieved by removing or replacing the insulating surfactant on the TiO 2 nanorods surface with a more conductive ligand, which can play the role to assist charge separation efficiency or also to prevent from back recombination, giving a large improvement in the short circuit current and fill factor. The relatively high power conversion efficiency of 2.2 % under simulated A.M. 1.5 illumination (100 mW/cm 2 ) can be achieved, providing a route for fabricating low-cost, environmentally friendly polymer photovoltaic devices by all-solution processes.

The characteristics of a nanocomposite consisting of the blue-emitting polymer polyfluorene and ZnO nanowires are reported. The electroluminescence spectrum of the white light emission is from about 400 nm to 750 nm.

In this work, we present the evolution of optical constants varying with distinct annealing temperature for poly (3- hexylthiophene) (P3HT) and 6,6-phenyl C61-butyric acid methyl ester (PCBM). With calculation of the transmission and reflection spectra in P3HT:PCBM photovoltaic device , the optical properties correlation to annealing temperature is studied. The solar cell power conversion efficiency and optical absorption is compared simultaneously. Finally, the electric field amplitude in the device is discussed for detailed explanation of thermal annealing effects on the organic photovoltaic device performance.