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Heterostructures, combining perovskite nanocrystals (PNC) and chalcogenide quantum dots, could pave a path to optoelectronic device applications by enabling absorption in the near-infrared region, tailorable electronic properties, and stable crystal structures. Ideally, the heterostructure host material requires a similar lattice constant as the guest which is also constrained by the synthesis protocol and materials selectivity. Herein, we present an efficient one-pot hot-injection method to synthesize colloidal all-inorganic cesium lead halide-lead sulfide (CsPbX 3 (X = Cl, Br, I)-PbS) heterostructure nanocrystals (HNCs) via the epitaxial growth of the perovskite onto the presynthesized PbS nanocrystals (NCs). Optical and structural characterization evidenced the formation of heterostructures. The embedding of PbS NCs into CsPbX 3 perovskite allows the tuning of the absorption and emission from 400 to 1100 nm by tuning the size and composition of perovskite HNCs. The CsPbI 3 -PbS HNCs show enhanced stability in ambient conditions. The stability, tunable optical properties, and variable band alignments accessible in this system would have implications in the design of novel optoelectronic applications such as light-emitting diodes, photodetectors, photocatalysis, and photovoltaics.

We report the high yield synthesis of about 11 nm sized CH 3 NH 3 PbBr 3 nanocrystals with near-unity photoluminescence quantum yield. The nanocrystals are formed in the presence of surface-binding ligands through their direct precipitation in a benzyl alcohol/toluene phase. The benzyl alcohol plays a pivotal role in steering the surface ligands binding motifs on the NC surface, resulting in enhanced surface-trap passivation and near-unity PLQY values. We further demonstrate that thin films from purified CH 3 NH 3 PbBr 3 nanocrystals are stable >4 months in air, exhibit high optical gain (about 520 cm -1 ), and display stable, ultralow amplified spontaneous emission thresholds of 13.9 ± 1.3 and 569.7 ± 6 μJ cm -2 at one-photon (400 nm) and two-photon (800 nm) absorption, respectively. To the best of our knowledge, the latter signifies a 5-fold reduction of the lowest reported threshold value for halide perovskite nanocrystals to date, which makes them ideal candidates for light-emitting and low-threshold lasing applications.

In this manuscript we reveal the formation of bilayered hybrid perovskites of a new lower dimensional perovskite family, (CHMA) 2 (MA) n-1 Pb n I 3 with n = 1-5, with high ambient stability via its crystallization driven self-assembly process. The spun-coated perovskite solution tends to crystallize and undergo phase separation during annealing, resulting in the formation of 2D/3D bilayered hybrid perovskites. Remarkably, this 2D/3D hybrid perovskites possess striking moisture resistance and displays high ambient stability up to 65 days. The bilayered approach in combining 3D and 2D perovskites could lead to a new era of perovskite research for high-efficiency photovoltaics with outstanding stability, with the 3D perovskite providing excellent electronic properties while the 2D perovskite endows it moisture stability.

Organic-inorganic lead halide based perovskites solar cells are by far the highest efficiency solution-processed solar cells, threatening to challenge thin film and polycrystalline silicon ones. Despite the intense research in this area, concerns surrounding the long-term stability as well as the toxicity of lead in the archetypal perovskite, CH3NH3PbI3, have the potential to derail commercialization. Although the search for Pb-free perovskites have naturally shifted to other transition metal cations and formulations that replace the organic moiety, efficiencies with these substitutions are still substantially lower than those of the Pb-perovskite. The perovskite family offers rich multitudes of crystal structures and substituents with the potential to uncover new and exciting photophysical phenomena that hold the promise of higher solar cell efficiencies. In addressing materials beyond CH3NH3PbI3, this Perspective will discuss a broad palette of elemental substitutions, solid solutions, and multidimensional families that will provide the next fillip toward market viability of the perovskite solar cells.

Organic-inorganic metal halide perovskite solar cells were fabricated by laminating films of a carbon nanotube (CNT) network onto a CH3NH3PbI3 substrate as a hole collector, bypassing the energy-consuming vacuum process of metal deposition. In the absence of an organic hole-transporting material and metal contact, CH3NH3PbI3 and CNTs formed a solar cell with an efficiency of up to 6.87%. The CH3NH3PbI3/CNTs solar cells were semitransparent and showed photovoltaic output with dual side illuminations due to the transparency of the CNT electrode. Adding spiro-OMeTAD to the CNT network forms a composite electrode that improved the efficiency to 9.90% due to the enhanced hole extraction and reduced recombination in solar cells. The interfacial charge transfer and transport in solar cells were investigated through photoluminescence and impedance measurements. The flexible and transparent CNT network film shows great potential for realizing flexible and semitransparent perovskite solar cells.

Solution processed zinc tin oxide (ZTO) thin film transistors (TFTs) were fabricated by varying the Zn/Sn composition. The addition of Sn to the zinc oxide (ZnO) films resulted in improved electrical characteristics, with devices of Zn0.7Sn0.3O composition showing the highest mobility of 7.7 cm(2)/(V s). An improvement in subthreshold swings was also observed, indicative of a reduction of the interfacial trap densities. Mobility studies at low temperature have been carried out, which indicated that the activation energy was reduced with Sn incorporation. Kelvin probe force microscopy was performed on the films to evaluate work function and correlated to the metal-semiconductor barrier indicating Zn0.7Sn0.3O films had the smallest barrier for charge injection. Organic-inorganic hybrid complementary inverters with a maximum gain of 10 were fabricated by integrating ZTO TFTs with poly-3-hexylthiophene (P3HT) transistors.

Chalcopyrite-based solar cell deposited by solution processes is of great research interest because of the ease of fabrication and cost effectiveness. Despite the initial promising results, most of the reported methods encounter challenges such as limited grain growth, carbon-rich interlayer, high thermal budget, and the presence of secondary Cu-rich phases, which limit the power conversion efficiency (PCE). In this paper, we develop a new technique to deposit large grain, carbon-free CISSe absorber layers from aqueous nanoparticle/precursor mixture which resulted in a solar cell with PCE of 6.2%. CuCl2, InCl3, and thiourea were mixed with CuS and In2S3 nanoparticles in water to form the unique nanoparticle/precursor solution. The Carbon layer formation was prevented because organic solvents were not used in the precursor. The copper-rich (CuS) nanoparticles were intentionally introduced as nucleation sites which accelerate grain growth. In the presence of nanoparticles, the grain size of CISSe film increased by a factor of 7 and the power conversion efficiency of the solar cell is 85% higher than the device without nanoparticle. This idea of using nanoparticles as a means to promote grain growth can be further exploited for other types of chalcopyrite thin film deposited by solution methods.

This paper describes the synthesis of ternary chalcogenide Cu(2)SnSe(3) nanocrystals as an alternative solar absorber material to conventional quaternary CuIn(x)Ga(1-x)Se(2). We used the hot coordination solvent method with hexadecylamine as the capping ligand for the first time for this material system. Using a variety of characterization techniques, such as X-ray diffraction, selected area electron diffraction, convergent beam electron diffraction, and Raman spectroscopy, the nanocrystals were found to be monoclinic Cu(2)SnSe(3) with an optical energy band gap of 1.3 eV and have a narrow size distribution. These nanocrystals are shown to be photosensitive in the range of wavelengths corresponding to the solar spectrum, which makes them highly promising as alternative photon absorber materials for photovoltaic applications.

Nanoclay minerals play a promising role as additives in the liquid electrolyte to form a gel electrolyte for quasi-solid-state dye-sensitized solar cells, because of the high chemical stability, unique swelling capability, ion exchange capacity, and rheological properties of nanoclays. Here, we report the improved performance of a quasi-solid-state gel electrolyte that is made from a liquid electrolyte and synthetic nitrate-hydrotalcite nanoclay. Charge transport mechanisms in the gel electrolyte and nanoclay interactions with TiO(2)/electrolyte interface are discussed in detail. The electrochemical analysis reveals that the charge transport is solely based on physical diffusion at the ratio of [PMII]:[I(2)] = 10:1 (where PMII is 1-propyl-3-methylimidazolium iodide). The calculated physical diffusion coefficient shows that the diffusion of redox ions is not affected much by the viscosity of nanoclay gel. The addition of nitrate-hydrotalcite clay in the electrolyte has the effect of buffering the protonation process at the TiO(2)/electrolyte interface, resulting in an upward shift in the conduction band and a boost in open-circuit voltage (V(OC)). Higher V(OC) values with undiminished photocurrent is achieved with nitrate-hydrotalcite nanoclay gel electrolyte for organic as well as for inorganic dye (D35 and N719) systems. The efficiency for hydrotalcite clay gel electrolyte solar cells is increased by 10%, compared to that of the liquid electrolyte. The power conversion efficiency can reach 10.1% under 0.25 sun and 9.6% under full sun. This study demonstrates that nitrate-hydrotalcite nanoclay in the electrolyte not only solidifies the liquid electrolyte to prevent solvent leakage, but also facilitates the improvement in cell efficiency.

Here we report the synthesis and characterization of a series of annelated benzotriazole based polymers with variable bandgap. Benzobistriazole monomers reported by us previously were desymmetrized using partial reduction ring opening followed by ring closure to produce a wide range of annelated benzotriazole based monomers. These monomers were co-polymerized with a fluorene moiety to give polymers with bandgaps ranging from 1.16 to 2.41 eV.

CdS(x)Se(1-x) nanobelts are interesting nanostructured materials with a tunable band gap from 1.7 to 2.4 eV depending on the nanobelts' stoichiometry. On the basis of their chemical compositions, these nanobelts give out strong photoluminescence with unique color. In this work, we demonstrate that a direct focused laser beam irradiation was able to achieve localized modification of the chemical composition of the nanobelts. As a result, we could locally change the optical properties of these nanobelts. With a scanning laser beam, micropatterns with a wide range of fluorescence color could be created on a substrate covered with ternary nanobelts without a prepatterned mask. The laser modified nanobelts showed higher resistance to acid corrosion and these nanobelts exhibited more superior photoconductivity. The construction of micropatterns with functionality/color control within the sample would provide greater building blocks for photoelectronic applications.

A low temperature route to synthesize graphene oxide-Pt nanoparticle hybrid composite by light assisted spontaneous coreduction of graphene oxide and chloroplatinic acid without reducing agent is demonstrated. Analysis indicates the importance of light as energy provider and ethanol as hole scavenger in the formation of small Pt nanoparticles (∼3 nm) on graphene oxide as well as graphene oxide reduction. Spray coating was used to deposit the hybrid material as a counter electrode in dye sensitized solar cells (DSCs). An efficiency of 6.77% for the hybrid graphene counter electrode has been obtained, higher than the control device made by low temperature sputtered Pt as counter electrode. Compatibility of the hybrid material with flexible plastic substrates was demonstrated yielding DSCs of an efficiency of 4.05%.

We report a unipolar operation in reduced graphene oxide (RGO) field-effect transistors (FETs) via modification of the source/drain (S/D) electrode interfaces with self-assembled monolayers (SAMs) of 5-(4-hydroxyphenyl)-10,15,20-tri-(p-tolyl) zinc(II) porphyrin (Zn(II)TTPOH) molecules. The dipolar Zn(II)TTPOH molecules at the RGO/platinum (Pt) S/D interface results in an increase of the electron injection barrier and a reduction of the hole-injection barrier. Using dipole measurements from Kelvin probe force microscopy and highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) calculations from cyclic voltammetry, the electron and hole injection barriers were calculated to be 2.2 and 0.11 eV, respectively, indicating a higher barrier for electrons, compared to that of holes. A reduced gate modulation in the electron accumulation regime in RGO devices with SAM shows that unipolar RGO FETs can be attained using a low-cost, solution-processable fabrication technique., (© 2012 American Chemical Society)

The one-pot synthesis of 4,8-dibromobenzo[1,2-d;4,5-d']bistriazole, followed by alkylation and Stille coupling to yield three different isomeric derivatives with markedly different optoelectronic properties, is reported. These derivatives show potential as new units in organic oligomers and polymers for electronics applications., (© 2011 American Chemical Society)

Polypyrrole(PPy) nanorod networks with a high electrical conductivity of 40 S cm(-1) have been obtained in a high yield by employing an ion association of heparin-methylene blue as a new morphology-directing agent. The polypyrrole nanorod networks are mixed with different content of carbon nanoparticles to make PPy nanorod networks/carbon nanoparticles(PPy/C) counter electrodes. It is found that the PPy/C composite with 10% carbon content shows a lower charge transfer resistance and better catalytic performance for the reduction of I(3)(-), compared with the pristine PPy and carbon electrodes. The better catalytic performance is attributed to the interaction of the superior electrocatalytic activity of the unique polypyrrole nanorod networks and the carbon nanoparticles, which can accelerate triiodide reduction and electron transfer in the electrode. Under standard AM 1.5 sunlight illumination, the dye-sensitized solar cell based on the PPy/C composite with 10% carbon content as the counter electrode demonstrates a high efficiency of 7.2%, which is much higher than that of pristine PPy and carbon electrode-based DSCs and comparable to that of the thermal decomposed Pt-based DSC., (© 2011 American Chemical Society)

The synthesis and characterization is reported of low bandgap [1,2,5]chalcogenazolo[3,4-f]benzo[1,2,3]triazole and [1,2,3]triazolo[3,4-g]quinoxaline derivatives that display higher solubility and stability then their thiadiazole counterparts, [1,2,5]chalcogenazolo[3,4-f]benzo[2,1,3]thiadiazole and [1,2,5]thiadiazolo[3,4-g]quinoxaline, respectively.

The reduction of a dithienylbenzobisthiadiazole derivative TBBT can be performed selectively so as to afford either [1,2,5]-thiadiazolo[3,4-g]quinoxaline (TQ) or pyrazino[2,3-g]quinoxaline (PQ) derivatives. This approach offers a much milder, shorter, and more efficient route to PQ and TQ derivatives than current methods. It is further shown how the optical and electrochemical properties of PQ and TQ can be tuned by choice of appropriate substituents.

A one-step synthesis of 4,8-dibromobenzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole with use of 1,2,4,5-tetraaminobenzene tetrahydrobromide and thionyl bromide in good yield is reported. This unit can then be used in the synthesis of low bandgap materials via palladium-catalyzed coupling reactions. The approach offers a quick and easy way to prepare low bandgap materials as compared to the current literature methods.

A direct process for preparing contiguous gold shells (15-25 nm thick) over amorphous silica spheres (200 nm) is described. In this method, gold seeds are synthesized from HAuCl(4) in a dilute NaOH solution using deposition-precipitation with subsequent metallization by sodium borohydride (NaBH(4)). The ease of dispersing gold nanocrystals on spheres of bare silica and spheres after grafting with ammonia was studied as a function of pH (4-8), reaction temperature (65-96 degrees C), and time (5-30 min). Additional parameters requiring optimization included the quantity of NaBH4 and the HAuCl(4) in K(2)CO(3) solution to silica volume ratio. The evolution of gold nanocrystal growth was monitored by transmission electron microscopy, and the bathochromic shift of ultraviolet-visible absorption was correlated with shell perfection and thickness.