Search

In the present work, ZnO nanoparticles were synthesized using chemical route method. Composition ratio for Zn:O and various oxidation states were determined using XPS (X-ray photoelectron spectroscopy) technique. The 1 hr calcined ZnO nanoparticles were found to the best due to their monodispersed nature (size ˜20 nm) and high purity. These nanoparticles were then used for synthesizing ZnO–CdSe nano-compounds. These nanocrystals were integrated with CdSe qdots (synthesized using Hot-Injection technique) of varied size (5 nm and 8 nm) via MPA (mercaptopropionic acid) as a linker to develop hybrid nano-compounds for photoactive applications like Quantum Dot sensitized solar cells (QDSSC’s) etc. Here, the main objective of the work was to explore the structure of hybrid nano-compounds. XPS-depth-profiling technique was used as an investigation technique for the compositional and structural analyses of ZnO–CdSe nano-compounds. The compositional structure was analyzed layer wise (obtained by etching at different time of sputtering) for the exact position of ZnO and CdSe nanoparticles. On the basis of above study utilizing depth profiling technique of XPS and TEM images, it was found that high quality of hybrid nano-compounds can be synthesized with smaller sized quantum dots, as compared to larger sized quantum dots because of unbounded phosphorus (P) and selenium (Se). Also, it confirms the role of linker that strengthens the binding of CdSe quantum dots on the surface of ZnO thus making it hard to separate the anchored, interstitial CdSe completely which paves the way for the development of stoichiometric, structurally and morphologically-stable ZnO–CdSe nano-compounds.

A new self-activated green-yellow emitting Gd₂CaZnO

This work reports the synthesis of varied shaped Cu2ZnSnS4 (CZTS) nano inks in a most stable kesterite phase via a hot injection colloidal route. CZTS nanoparticles of varied shape were synthesized by using various capping ligands with the introduction of butylamine as a new capping ligand and two different sulfur precursors respectively. The shape of the as-synthesized kesterite CZTS nanocrystals can be well controlled in the form of nanofibers, spherical nanoparticles, nano hexagons, nanotriangles, and nanodiscs. A detailed analysis of the effects of various capping ligand and sulfur source on reaction conditions to obtain pure phase kesterite CZTS nanocrystals for different shapes is explained using LaMer's diagram. It has been found that the choice of sulfur precursor also plays an important role in determining the symmetry and orientation of the plane of the CZTS nanocrystals. Due to different morphology and capping ligands present on the surface, diverse surface properties were obtained which was confirmed by contact angle measurements. The variation in the band gap was also found with changes in morphology of kesterite phased CZTS nanoparticles. Due to variations obtained in band gap, changes in I-V characteristics were also observed which may leads different CZTS nanoparticles to have their potential applications in different regime other than photovoltaics like sensors, photocatalysis etc.

In indium phosphide quantum dots (InP QDs), the presence of surface states due to unbonded indium or phosphorus atoms quenches its photoluminescence (PL) efficiencies. Hence, it is imperative to passivate these surface states to achieve high photoluminescence efficiencies of InP nanocrystals. In this work, a novel post-synthesis nascent H chemical treatment to enhance the quantum yield of single-pot, wet chemical route synthesized InP QD's is reported for the first time. The main advantages of this post-synthesis treatment are: (i) it is easy, inexpensive and reproducible and (ii) it does not involve harsh chemical treatment viz. dipping of InP QDs in HF-based solutions, nor it requires annealing at high temperatures which may be detrimental to the fragile structure of InP. The significant increment in PL intensity upon aforementioned hydrogen treatment is due to the passivation of surface states and structural recrystallization mechanism that promotes radiative recombination of electrons and holes and hence higher lifetime values. An enhancement in PL intensity of as-synthesized InP QDs upon nascent hydrogen treatment is quite remarkable and is even better than that accomplished by InP-ZnS core-shell QDs with similar size-distribution. The hydrophobicity of H-treated InP QD's is found to be more than untreated InP thus implying higher compactness and structural rigidity similar to as achieved by InP-ZnS core-shell QDs. Mechanisms related to nascent hydrogen treatment, photo-oxidation and PL enhancement and its effect on the surface stoichiometry of InP QDs are discussed via structural, morphological, compositional and optical studies corroborated by various complementary techniques viz. SEM, HRTEM, EDAX,NMR, DLS, Zeta Potential, Contact Angle, PL and Transient Absorption respectively. The application of InP films as a humidity sensor has been demonstrated and untreated InP film in particular shows higher sensitivity values upon exposure to humid treatment as compared with H-treated InP and InP-ZnS core-shell QD's respectively.

In this work, stable Cu2ZnSnS4 (CZTS) nanocrystals (NCs) in pure kesterite phase were synthesized by a facile one-pot rapid injection technique (colloidal route). Time-dependent reaction mechanism for the synthesis of CZTS nanoparticles is explained. When TOP-S (Tri-octyl phosphine–sulphur) was injected in the CuZnSn-complex with TOPO (Tri-octyl phosphine oxide) as capping ligand, orthorhombic phase Cu2−XS nanoparticles of spherical shape were found at nucleation sites. With an advancement in the reaction time, Sn got infused in Cu2−XS to form Cu2SnS3 and its shape got deformed. Further increase in reaction time infuses Zn to form Cu2ZnSnS4 with the gradual vanishing of Cu2−XS and Cu2SnS3 phases and finally, the rod-shaped CZTS Np’s were obtained. This factor of reaction time, which influence the morphology and size were studied in detail. The structural and optical properties of the pure kesterite phase CZTS nanorods were also analysed. The band gap of the rod-like CZTS is determined to be around 1.43 eV, which is an optimum value for solar photoelectric conversion.

A quintessential perspective for elaborating the pivotal role of quinary chalogenides such as CZTSSe plunges the thrust for exploration of non-vacuum approach for development of multicomponent chalcogenides utilizing organic surfactants and solvents for the nanocrystals ideal for photovoltaic applications. The piece of study envisages employment of TOPO-TOP as capping agents-cum-solvents for the very first time and have not been reported for CZTSSe-based materials till date. The work has been forwarded with the variation of anionic ratios in pristine counterparts of CZTSSe; i.e. CZTSe and CZTS in order to envision the potential of quinary chalcogenides wherein properties of two different materials coalesce to impart improved characteristics in CZTSSe. Varying Se:S ratios gradually during nanocrystals' synthesis by high-temperature colloidal route ensued precise control over the phase formation and morphology. With the employment of these capping agents, as-synthesized nanocrystals' are inherently Se-rich and high crystallinity restrains the need for selenization and high temperature annnealing respectively.

Recent study investigates employment of differently-capped chalcopyrite Copper Indium Gallium Diselenide (CIGSe) wherein; binding abilities of three different capping ligands have been studied. Oleylamine (OLA), Oleic acid (OA) and the combination of oleylamine-oleic acid (OLA+OA) have been chosen as basic ligands in addition to dodecanethiol as a source for attaining Se dissolution that is otherwise difficult during utilization of pristine ligands. The overall combination has also led to the formation of well-stabilized nanocrystals. The work also envisages an approach towards low-cost, environmentally-friendly processing of active absorber CIGSe layers by various parametric variations; emphasizing primarily on the adoption of green route method for overcoming the toxicity constraints in the preparation of CIGSe nanocrystals.

The present study focuses on the impacts of annealing temperature in different ambiances on the morphological behavior and thin-film quality of CZTS nanoparticles. CZTS nanoparticles have been synthesized via the hot-injection colloidal route method. CZTS nanoparticles have been annealed in air, vacuum atmosphere, and sulphur environment (N2 + H2S(5%), respectively at 450 °C for 30 min. The structural, morphological, compositional, and optical properties of all CZTS thin films were analyzed. The volume fraction is increased in the vacuum annealed thin film keeping crystallite size as same as in the as-deposited film. This results in a reduction of cracks and voids and thus the surface defects of the vacuum annealed thin film as confirmed by scanning electron microscope (SEM). AFM also confirms the improved quality of CZTS thin film annealed in a vacuum. PL curves also confirm the minimum defects in the case of vacuum-annealed thin films. Thus, the study reveals that the best quality CZTS thin films i.e. films with the least pinholes, cracks, and voids without any significant change from the initial conditions can be obtained after annealing in the vacuum environment.

For colloidally stable nanoparticle dispersions, it is imperative that some sort of interparticle repulsion is introduced to balance or overcome the ever-present van der Waals forces of attraction. In the present work, we have demonstrated that an efficient stabilization of a TiO2 nanoparticle dispersion depends upon the pH and zeta potential which are influenced by the route of synthesis (aqueous or ethanol based) and by the addition of suitable polymeric dispersants. In this work, both pH and zeta potential of the TiO2 nanoparticles have been accredited as a good index of the magnitude of the interaction between colloidal particles and their measurements are used to assess the stability of TiO2 and polymer/TiO2 composite colloidal systems synthesized via different routes. The concept of steric and electrostatic stabilization of colloids for both TiO2 (aqueous) and TiO2 (ethanol) systems and its corresponding polymer nanocomposites has been explained appropriately by means of a pictorial model. The efficient charge transfer across the polymer-TiO2(aqueous) interface as inferred from photoluminescence quenching measurements meets the desired criteria for the selection of TiO2(aqueous) materials for hybrid organic photovoltaic devices.

In this work, the effect of surface passivation of InP quantum dots (QDs) synthesized by the unconventional tri-n-octyl phosphine (TOP) route, on the structural and optoelectronic properties of their respective polymer nanocomposites, has been demonstrated by dispersing untreated and nascent hydrogen-treated InP QDs in P3HT polymer matrix, respectively. The surface passivation of InP QDs imparts photostability to its corresponding polymer–InP composite as a consequence of a better hydrogen passivation of defects acting as non-radiative recombination centres and can be achieved by employing a simple post-synthesis chemical treatment which is fast, reliable and reproducible. Here, with the distinctive usage of TOP both as a capping ligand and a source of phosphorus in conjunction with a novel chemical treatment, the quantum yield of InP QDs can be significantly enhanced and promotes charge transfer across donor (polymer)–acceptor (InP QDs) interface as supported by photoluminescence (PL) quenching studies as well. The increment in PL intensity upon incorporation of untreated InP QDs into the P3HT polymer matrix can be attributed to the dominance of Forster energy transfer between host P3HT polymer (donor) and guest InP nanocrystals (acceptors) in polymer/InP (untreated) composites. The mechanisms of energy and charge transfer in polymer–InP (u/t) based composites is depicted pictorally. The importance of these two different processes observed in polymer/InP (untreated) and polymer/InP (treated) composites is that it makes them useful for organic optoelectronic, i.e. electroluminescent and photovoltaic devices, respectively.

In this work, charge/energy transfer characteristics of PEDOT:PSS-TiO2 composites have been studied as a function of crystallite sizes of TiO2 nanocrystals annealed at different temperatures for its application in organic optoelectronic devices. From this we found that as the temperature increases energy transfer phenomenon dominates over charge transfer process. We raised the temperature from 200 to 400 °C. Charge transfer process observed at 200 °C and energy transfer process dominated at 400 °C.

In this work, ternary CuInSe 2 (CISe) chalcopyrite nanocrystallites efficiently passivated by a novel combination of capping agents viz: aniline and 1-octadecene during chemical route synthesis were dispersed in conducting polymer matrix poly(3-hexylthiophene) (P3HT). By varying the composition and concentration of the ligands, the properties of the resulting CISe nanocrystallites and its corresponding polymer nanocomposites thus could be tailored. The structural, morphological and optical studies accomplished by various complimentary techniques viz. Transmission Electron Microscopy (TEM), Contact angle, Photoluminescence (PL) and Raman have enabled us to compare the different hybrid organic (polymer)-inorganic nanocomposites. On the basis of aniline–octadecene equilibrium phase diagram, the polydispersity of the CISe nanocrystals could be tuned by using controlled variations in the reaction conditions of nucleation and growth such as composition of the solvent and temperature. To the best of author’s knowledge, the beneficial effects of both the capping agents; aniline and octadecene contributing well in tandem in the development of large-sized (100–125 nm) high quality, sterically- and photo-oxidative stable polycrystalline CISe and its corresponding polymer (P3HT):CISe composites with enhanced charge transfer efficiency has been reported for the first time. The low-cost synthesis and ease of preparation renders this method of great potential for its possible application in low-cost hybrid organic–inorganic photovoltaics.

In present study, we have explained the detailed synthesis chemistry of perovskite material SrTiO3 and the role of annealing temperature on its phase transition, which has not been reported till date. Rare-earth ion Eu was explored as a dopant and its concentration was optimized for achieving maximum luminescence. At annealing temperature of 600 °C, mixed phase consisting of TiO2, SrCO3 and Eu2O3 was observed in the XRD pattern, which eventually vanished at 1000 °C and a pure phase of SrTiO3 was obtained. Besides this, the SrTiO3 undoped and Eu doped samples were synthesized in bulk as well as nano forms, to study their structural, morphological and optical behavior. The SrTiO3:Eu optimized sample annealed at 1000 °C exhibited maximum luminescence due to improved crystallinity and phase purity of the host lattice. The synthesized perovskite sample can have multidisciplinary applications in advanced areas of photovoltaics.

In this study, europium (Eu) and dysprosium-(Dy) doped phosphors, i.e., ZnO:Eu, ZnO:Dy, and Eu:Dy co-doped zinc oxide (ZnO:Eu, Dy) semiconductor phosphors, with optimized concentrations, were synthesized using the conventional solid-state reaction method in an oxygen environment. Detailed structural, morphological, and compositional investigations were conducted using X-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive X-ray measurements, respectively. Photoluminescence (PL) emission spectra were recorded under different excitation wavelengths to assess the optical characteristics. Electrical analysis was conducted using an inductance (L), capacitance (C), and resistance (R) (LCR) meter and a Keithley source meter, and magnetic analysis was performed using a vibrating sample magnetometer (VSM). XRD confirmed the presence of Eu and Dy ions because the diffraction peaks matched perfectly with those for Eu2O3 and Dy2O3, respectively. The PL results indicated the broad emissions from the samples in the visible region (400–700 nm) under different ultraviolet excitation wavelengths. The VSM results demonstrated that both the Dy-doped and Eu:Dy co-doped ZnO samples exhibited paramagnetic behavior at room temperature, but not the undoped and Eu-doped ZnO samples. The ZnO:Dy sample had superior parameters in terms of the electrical measurements such as the AC/DC conductivity, capacitance, current density, and dielectric constant compared with the ZnO:Eu and ZnO:Eu, Dy samples. These detailed investigations of the optical, magnetic, and electrical properties demonstrate that ZnO:Dy and ZnO:Eu, Dy may be promising materials for use in optical devices.

Long non-coding RNAs are in general described as transcripts >200 nt and lacking potential to code for proteins. In the present study, 7613 putative lncRNAs were identified in Brassica juncea genome using in silico approaches. Of these, 1614 lncRNAs were found to be differentially expressed in response to heat and drought stress conditions. Further, we characterized these lncRNAs and performed functional annotation based on co-expression analysis strategy and pathways enrichment analysis. On these bases, the identified abiotic stress-responsive lncRNAs were found to be associated with important pathways including both enzymatic and non-enzymatic antioxidants such as glutathione metabolism, phenylpropanoid biosynthesis, cysteine metabolism, etc. Moreover, lncRNAs were also found to co-express with transcription factors associated with abiotic stress response. Finally, those lncRNAs were identified that could act as putative targets and endogenous target mimics of miRNAs involved in response to heat and drought. Further investigation could be carried out for select lncRNA candidates like those for which quantitative polymerase chain reaction analysis was performed in this study or for those which were estimated as promising modulators of stress response based on miRNA-lncRNA interaction studies. Overall, our study highlights the potential role of lncRNAs in B. juncea in response to both heat and drought stress and can help elucidate the mechanism of tolerance to these abiotic stress conditions in the oil seed crop.

ZnO being most avid semiconductor metal oxide with a wide band gap of 3.37 eV. ZnO nanostructures were synthesized in the shape of nano rods and flowers to finds their proficiency in the field of photocatalysis and photovoltaics. ZnO nanostructures were investigated in the shape of nano rods and flowers by, X Ray Diffractometer (XRD) confirms pure hexagonal wurtzite structure of ZnO, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images showed high crystalline morphology and the formation of nano rods and flowers. Ultraviolet and Photoluminescence (PL) study confirms the absorption at 375, 371 nm for ZnO rods and flower which leads to an increase in the band gap and the peak observed at the violet, blue and green emission. The peaks shift is due to increase in defect in flower nanostructures of ZnO, Dynamic Light Scattering (DLS) calculated the average particles size 617 and 823 nm for rods and flower respectively. Conductivity analysis prove that nano flowers are more conductive having more defects and large number of photocatalytic active sites and large number of electron-hole pairs make best suited for photocatalytic specie. Thus, ZnO nano flowers were observed ideal for photocatalysis and photovoltaic applications due its large number of active sites and defects.

Green emitting Ba2SiO4:Tb3+ crystalline semiconducting powders have been synthesized using modified solid-state reaction technique.Synthesized Ba2SiO4:Tb3+ phosphor powders were characterized structurally and morphologically by employing X-ray diffraction (XRD) and Scanning electron microscopy (SEM) techniques. The photoluminescent characterization identified that the sample exhibits intense green photoluminescence (PL) emission with several peaks in the range (490−622 nm) which are attributed to the 5D4-7Fj transition of Tb3 + . The excitation spectrum identified that the sample has a broad excitation ranging from UV to visible (350−500 nm). Additionally, the CIE coordinates were calculated to determine its color purity. PL measurement revealed that the synrthesised phosphor shows significant overalapping with commonly used Polymers and small-molecules used in organic solar cells. The detailed structural, morphological and photoluminescence characterization revealed that the material is a potential candidate for for solid-state lighting and photovoltaic applications.

Wet-route synthesis of CuInSe2 (CISe) nanocrystals has been envisaged with the utilization of the unique combination of coordinating ligand and non coordinating solvent. Our work demonstrates the formation of a single-phase, nearly stoichiometric and monodispersive, stable and well-passivated colloidal ternary CISe nanocrystals (band gap (Eg)~1.16 eV) using a novel combination of ligands; viz. volatile arylamine aniline and non-volatile solvent 1-octadecene. The synthesis and growth conditions have been manoeuvred using the colligative properties of the mixture and thus higher growth temperature (~250 °C) could be attained that promoted larger grain growth. The beneficial influence of the capping agents (aniline and 1-octadecene) on the properties of chalcopyrite nanocrystals has enabled us to pictorally model the structural, morphological and optoelectronic aspects of CISe nanoparticles.

As-grown and chemically reduced Rh-doped (1500 p.p.m.) KnbO3 single crystals grown by the Czochralski method have been characterized. Reduction of the grown crystals at different levels was carried out under a mixture of CO and CO2 gases as the crystals were grown with excess oxygen. The effect of reduction and poling on crystalline perfection was studied by high-resolution X-ray diffraction (HRXRD) using a multi-crystal X-ray diffractometer developed in-house. The diffraction curves of the as-grown, electrically poled, moderately reduced and heavily reduced single-crystal specimens show remarkable differences. The studies by HRXRD reveal that poling has some influence on the improvement of crystalline perfection, while chemical reduction has a great influence on crystalline perfection; at moderate reduction the crystal becomes nearly perfect, but when the reduction is very heavy the crystal quality decreases slightly, although it is still better than for unreduced samples. Asymmetry of the diffraction curves with respect to the peak position reveals that the as-grown specimens contain a high concentration of both vacancies and self-interstitials. After poling, the concentration of self-interstitial defects is lowered to some extent. When the specimen is moderately chemically reduced, the scattered intensity on both sides of the peak is greatly reduced, showing that the concentrations of both vacancies and interstitials are reduced to a great extent owing to chemical reduction. This clearly indicates that, as a result of the chemical reduction of oxygen in the crystal, crystalline perfection is enhanced significantly. However, under heavy chemical reduction, the number of vacancy defects is increased to a significant extent. Raman scattering, dielectric and photoluminescence studies also show interesting features, with excellent correlation with the degree of crystalline perfection influenced by the processes of reduction and poling.

In this work, Copper Indium disulfide (CIS) nanoparticles of size ∼ 5 nm were prepared via solvothermal approach in ethanol under the nitrogen atmosphere using copper chloride, indium chloride and thiourea (Tu) as starting materials, without any assistance through organic ligands at the reaction temperature of 150 °C. The factors which might affect the morphology, structure, phase of the product during the synthesis were discussed. It was found that the products were significantly affected by the reaction time and solvent. The morphology, structure, phase constituents and optical properties of the as prepared CIS powders were characterized by X-ray diffraction (XRD), Energy dispersive Spectroscopy (EDS), scanning electron microscopy (SEM) and ultraviolet–visible (UV–Vis) spectrometry respectively. The result shows that the CIS nanoparticles can be synthesized by solvothermal method at a reaction time of 2 h and shows that when the reaction time was increased from 2 h to 48 h, CIS porous flower like nanoparticles were obtained as we increase the reaction time. We also observed that in this process, the phase selection of WZ-CIS or CH-CIS is greatly influence by solvent. We also observed that, in this process sulfur source did not influence the phase but participated in the growth of the nanoparticles.

In this work, it has been demonstrated that a systematic combination of the reaction and growth conditions allows the possibility to produce high quality PbSe nanocrystals over a broad range of diameters with narrow size distributions without resorting to any size selective precipitation techniques. Effect of capping agents and critical growth parameters such as injection and growth temperature on the morphology of PbSe nanocrystallites is analyzed and discussed in terms of Efros'effective mass approximation theory and Wang's hyperbolic band model respectively. It is found that a hyperbolic Wang's band model is sufficiently accurate to explain the size quantization effects of PbSe nanocrystals. The capping agent/ligand (tri-n-octylphosphine and oleic acid mixture) helps to control the grain growth of the nanocrystals during its formation and increases the dispersibility of the nanocrystals in conducting polymer matrices viz. poly[2-methoxy, 5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly(3-hexylthiophene) (P3HT) for its application in photovoltaics.

In this work, a suitable ligand-exchange process has been proposed which elucidates the possibility to modulate charge/energy transfer rate between polymer and semiconductor quantum dots. The photoluminescence studies of CdSe emission as well as transient absorption measurements confirm mainly electron transfer for P3HT:CdSe (TOPO) and electron/energy transfer for P3HT:CdSe (OA) nanocomposites, respectively. The dominance of charge transfer for P3HT:CdSe (TOPO) as compared to P3HT:CdSe (OA) nanocomposites can be attributed to complete and partial removal of the surface ligands (TOPO, OA) upon ligand exchange with pyridine as elucidated from FTIR results. The various characterization techniques viz. Fourier transform infrared (FTIR), Raman, photoluminescence (PL), optical and transient absorption (UV-Vis and TA) spectroscopies used in this work provide an insight into the charge separation, charge accumulation and/or trapping of charge carriers for the better understanding of hybrid organic-inorganic photovoltaics. Composites of CdSe (OA) quantum dots in particular with P3HT polymer owing to its higher crystallinity and ordered morphology provide a new and promising direction toward developing effective light energy harvesting strategies in organic photovoltaics.

Here, we report a luminescent cathode buffer layer (CBL) for power conversion efficiency (PCE) enhancement of organic solar cells (OSCs). ZnO doped with Aluminum (Al) and Europium (Eu) was cast as CBL by a solution-processed method. CBL serves a dual purpose by acting both as a spectral conversion and an electron transporting layer. The luminescent ZnO:Al,Eu CBL layer has broad absorption spanning the ultraviolet (300–400 nm) spectrum, contributing to absorption enhancement. Moreover, the emission of CBL layer overlaps with the absorption of poly [N -9′-heptadecanyl-2,7-carbazole- alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) polymer thus elevating the overall absorption of the active layer and improving the photocurrent. With this ZnO:Al,Eu CBL in the inverted device configuration (ITO/CBL/active layer/MoOx/Al), an enhanced power conversion efficiency (PCE) of 6.9% was obtained while the device with pristine ZnO as CBL showed PCE of 5.9%. A blend of PCDTBT donor and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) acceptor was used as an active layer in both the cases. In ZnO:Al,Eu CBL layer, Al doping improves the conductivity, while Eu doping significantly enhances the emission in the visible region by down-shifting the incoming solar UV light to the visible range which overlaps with the absorption of PCDTBT polymer resulting in energy transfer and improved overall device efficiency. The findings of the study show the significance of luminescent ZnO:Al,Eu nanoparticle CBL in enhancing the performance of organic solar cells.

In this study, a colloid of nanocrystalline ZnO particles prepared by chemical route is sprayed on porous silicon layers. Porosity and thickness of PS layers were estimated by gravimetric analysis. Upon adsorption of ZnO colloids on PS films, oxidation of nanocrystalline Si causes shrinkage of the Si-core due to the breaking of Si Si bonds resulting in a blue-shift in PL spectra. The PL blue-shift can also be related to Si O species or due to defects and the silica networks on which OH groups are absorbed due to ZnO incorporation as also supported by our Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) studies, respectively. From high resolution X-ray diffraction (HRXRD) studies, a better crystalline perfection and considerable reduction in stress/strain values were observed for PS/ZnO layers as compared to virgin PS layers. The changes in the chemical composition at the surface of PS upon adsorption of ZnO colloids as elucidated by FTIR and XPS studies could be responsible for different PL emission and lattice-mismatch characteristics. The improved stability properties of PS are attributed to the strong absorption/adsorption of ZnO into the highly porous vertical layers separating macroscopic domains of nanoporous silicon and the mechanism of light emission from PS/ZnO layers is discussed on the basis of proposed energy band gap diagram.

For an optimum charge/energy transfer performance of hybrid organic–inorganic colloidal nanocrystals for applications such as photonic devices and solar cells, the determining factors are the distance between the nanocrystal and polymer which greatly depends upon nanocrystal size/nanocrystal ligands. Short chain ligands are preferred to ensure a close contact between the donor and acceptor as a result of the tunnelling probability of the charges and the insulating nature of long alkyl chain molecules. Short distances increase the probability for tunnelling to occur as compared to long distances induced by long alkyl chains of bulky ligands which inhibit tunnelling altogether. The ligands on the as-synthesized nanocrystals can be exchanged for various other ligands to achieve desirable charge/energy transfer properties depending on the bond strength of the ligand on the nanocrystal compared to the replacement ligand. In this work, the constraints involved in post-synthesis ligand exchange process have been evaluated, and these factors have been tuned via wet chemistry to tailor the hybrid material properties via appropriate selection of the nanocrystal capping ligands. It has been found that both oleic acid and oleylamine (OLA)-capped cadmium selenide (CdSe) quantum dots (QDs) as compared with trioctylphosphine oxide (TOPO)-passivated CdSe QDs are of high quality, and they provide better steric stability against coagulation, homogeneity, and photostability to their respective polymer:CdSe nanocomposites. CdSe QDs particularly with OLA capping have relatively smaller surface energies, and thus, lesser quenching capabilities show dominance of photoinduced Forster energy transfer between donors (polymer) and acceptors (CdSe nanocrystals) as compared to charge transfer mechanism as observed in polymer:CdSe (TOPO) composites. It is conjectured that size quantization effects, stereochemical compatibility of ligands (TOPO, oleic acid, and oleyl amine), and polymer MEH-PPV stability greatly influence the photophysics and photochemistry of hybrid polymer–semiconductor nanocomposites.

CuInS2 (CIS) particles were directly synthesized in P3HT matrix with different concentrations ratio of P3HT and CIS (1:2, 1:4, and 1:8) by decomposition of copper indium xanthate (CIX). Here, copper indium xanthate and P3HT were mixed homogeneously in o-dichlorobenzene (DCB), which induced the formation of the CIS nanoparticles by the thermal decomposition of the precursor compound in situ at temperatures as low as 110 °C. The effects of the precursor concentration on the size of the CIS nanoparticles was studied by microstructure investigations (TEM, AFM, XRD) and UV–vis measurements show that these CIS composites possess a direct bandgap energy higher than 1.45 eV depending on the concentration of P3HT. PL quenching of P3HT polymer (i.e., higher accessible fraction of fluorophores) was found to be more for in situ rather than ex situ conditions for comparable CIX concentrations or particle size. This can be attributed to the fact that in in situ synthesis, P3HT act as surface directing template for CIS nanoparticles which is not so in the case of ex situ synthesis. Due to this, the polymeric stabilization of the CIS nanocomposites is better realized for in situ synthesis as compared to ex situ synthesis.

InP quantum dots (QDs) and InP/ZnS core shell structures were synthesized using one pot hot injection technique. An increment in the PL intensity was seen after the growth of ZnS shell. A post synthesis HF treatment is given to the QDs in order to increase the PL intensity by removing surface defects. Humidity studies were done to observe the stability of InP QDs, treated InP and InP/ZnS QDs. An unusal increment in the PL intensity was observed for InP upon exposure to humidity. Within two weeks the PL intensity increased by 118 % without much change in the peak position. This can be attributed to the water molecules which get adsorbed on the surface of QDs and results in surface passivation. A similar trend was observed for treated InP QDs but in the second week, the PL increment was saturated and did not increase further. InP/ZnS showed a decrement in the PL intensity on exposure because it is robust to oxidation due to the formation of shell.

In recent years, kesterite structured Cu2ZnSn(S, Se)4 materials have attracted significant interest as second generation solar cell material. However, the capability of reproducibly synthesizing these nanocrystal (NC) inks with accurately controlled and specific compositions is very crucial for making efficient solar cell devices. In this work rod shaped CZTS nanoparticles are synthesized by cost effective and rapid hot injection technique using TOPO-TOP as capping ligand for various Zn/Sn precursor ratios. Since, for good solar cell device material (here, CZTS nanocrystals) higher zinc concentration are required so here, we varies zinc concentration and we find that mere increase in zinc amount in precursors for the synthesis of CZTS nanocrystals may not be necessarily advantageous for solar cell application. It should be optimized with respect to tin (Sn), phosphorus (P) and copper (Cu) for best PV properties and we find that incorporation of zinc into CZTS is higher in case where zinc amount is less in precursors. Different aspects of these nanorods are analyzed by EDAX, contact angle , transmission electron microscopy (TEM) and photoluminescence spectroscopy respectively.

TiO2 NPs synthesized via aqueous route shows better photocatalytic activity as compare to doped TiO2 NPs. The presence of dopants inhibits the recombination of exciton. The photocatalytic activity of the nanomaterial have been reduced because of less adsorption sites are available for MB dye due to increase surface coverage of nanomaterial by increase in Cr loading and thus less degradation is shown by doped material. Undoped TiO2 nanoparticles shows complete degradation of MB in 90 min, whereas doped TiO2 takes 120 min for complete degradation. The results suggested as higher concentration of dopant material leads to reduction in photocatalytic efficiency.

In the present study, the objective of this work has been two-fold: (i) To render CdSe QDs water-soluble for its possible application in biosensors , ligand-exchange process has been initiated. Here, the surface engineering of CdSe QDs synthesized with different hydrophobic ligands (TOPO/TOP, Oleic acid/TOP) has been done using organic primary aliphatic amine (butyl amine); and (ii) For different applications of hybrid organic MEH-PPV-inorganic CdSe composites in organic electronic devices such as efficient electroluminescent (OLED) and photovoltaic (OPV) devices, a suitable non-ligand purification process has been attempted. Here, the studies of hybrid nanocomposites demonstrate the dominance of mainly energy transfer between host polymer (donors) and guest as-synthesized CdSe nanocrystals (acceptors) for OLED applications and an enhanced charge transfer upon purification of CdSe QDs in their corresponding polymer nanocomposites for OPV applications respectively. The ease of removal of the ligands (TOPO/OA) from the surface of CdSe QDs either through direct ligand-exchange through Butyl-amine or through non-ligand exchange through purification process dictates its role in biosensors and in conjunction with polymer (MEH-PPV) in OLED and OPV devices respectively.

A comparative study on CIGSe nanocrystals prepared by two different ligands has been envisaged. This piece of study aims at comparing the properties obtained when toxic as well as non-toxic ligands are used for CIGSe, which is a potential photovoltaic material with performance at par with Si-based photovoltaics.

Chalcopyrite Cu (InxGa1−x) Se2 is a low-cost and potential alternative to present thin film silicon based photo-voltaic (PV) technology. Studies on nanocrystals of CIGSe prepared via colloidal route method with different capping agents, viz., oleylamine (OLA) and oleic acid (OA) have been done systematically. An exploration for binding abilities and plausible mechanism for the interaction between nanocrystals and capping agents employed has been envisaged.

Now a days, inorganic nanoparticles are gaining importance and are potential candidate in different organic electronic device application like (LEDs, PVs) due to their novel properties and confinement in Nano-dimensions. [1, 2]In the present work, we have compared the properties of titanium di oxide (TiO2) nanoparticles (NPs) synthesized by using two different chemical routes aqueous and ethanol respectively. These synthesized TiO2 nanoparticles have been characterized by X-ray diffraction spectroscopy (XRD) for phase confirmation. It was observed that synthesized nanoparticles are in anatase phase for both preparation routes.Morphological information was collected by scanning electron microscopy (SEM) which confirms that particles are almost spherical in shape and distributed uniformly which is further ensured by transmission electron microscopy (TEM). Dynamic light scattering (DLS) technique was also used for further confirmation of size distribution of as-synthesized nanoparticles. Optical properties w...

In this work, fourier transform infra-red (FTIR), photoluminescence (PL), optical and transient absorption (UV–vis & TA) spectroscopies have been used to monitor charge transfer from excited conjugated polymer (MEH-PPV) to smaller sized (5–7 nm) monodispersive CdSe quantum dots (QD) prepared by the chemical route using different capping ligands as trioctyl phosphine oxide (TOPO) and oleic acid (OA). CdSe (OA) QD's (∼7 nm) owing to its relatively smaller surface energies compared with CdSe (TOPO) QD's (∼5 nm) shows lesser quenching capabilities within the MEH-PPV polymer matrix. These studies demonstrate dominance of respective processes of photoinduced Forster energy transfer between host polymer (donors) and guest CdSe nanocrystals (acceptors) in polymer:CdSe(OA) nanocomposites and charge transfer in polymer:CdSe(TOPO) nanocomposites. Due to limitations of our nanosecond laser flash photolysis apparatus, transient absorption signatures of positive polaron of MEH-PPV could not be detected since it exhibits characteristic absorption in the mid-IR region. However, signatures of transient corresponding to CdSe−⁎ radical in the visible region was seen only when the sample was excited in the presence of polymer (MEH-PPV). A model has been proposed, which elucidate the possibility to modulate charge/energy transfer rate between polymer and semiconductor quantum dots using a suitable ligand-exchange process. The various characterization techniques used in this work provide an insight into the charge separation, charge accumulation and/or trapping of charge carriers for the better understanding of hybrid organic–inorganic photovoltaics.

In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe) chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO) and tri-n-octylphosphine (TOP) and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene) polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern–Volmer quenching constant (KSV) and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor–acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe). Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications.

In this work, we demonstrate the effect of surface modification of as-synthesized oleylamine-capped spherical CdSe QDs of size (5-7 nm). The as-prepared CdSe QDs are highly luminescent, monodispersive and exhibit energy transfer effects upon their dispersion in MEH-PPV polymer matrix. However, repetitive washing of CdSe QDs upon suitable chemical treatment leads to enhancement in charge transfer process as observed in their corresponding MEH-PPV: CdSe nanocomposites. Here, no evidence of agglomeration effects and surface states were found. This enhancement in charge transfer is mainly due to the partial removal of oleylamine capping ligand, which acts as a hindrance in the interaction between polymer and CdSe QDs. The importance of this study is that as-synthesized CdSe QDs show effective energy transfer whereas after chemical treatment, it shows enhanced charge transfer mechanism which makes their corresponding nanocomposites useful for different applications in organic electronic devices such as efficient electroluminescent (OLED) and photovoltaic (OPV) devices respectively.

In our work, we demonstrate the use of Copper Indium Gallium Diselenide(CIGSe) nanocrystals as electron acceptor in conducting polymer POLY(3-HEXYLTHIOPHENE)(P3HT) AND POLY(P-PHENYLENE VINYLENE) (PPV). We study the photo-induced charge separation and photostability of CIGSe-conducting polymer nanocomposites for the application of solar cells. CIGSe with P3HT ensures efficient charge transfer process across polymer-CIGSe interface as evident from higher quenching of Photoluminescence(PL) emission and higher value of rates of PL decays(PL/PLi), Stern-Volmer quenching constant K vs and number of accessible fluorophores( F a ), as compared to MEH-PPV polymer. P3HT polymer owing to its crystalline lamellar structure and ordered morphology impart stability to CIGSe composite. Hence superior morphology and photostability as compared to MEH-PPV:CIGSe nanocomposites. P3HT:CIGSe nanocomposites may be exploited as potential active layer in photovoltaic and photoelectrochemical devices.

This article addresses on the issue of oxidation on the organically capped CdSe nanoparticles. The surface states properties of the nanoparticles were monitored as a function of time during the natural exposure to oxygen and light, to determine the long term stability of the CdSe quantum dots. CdSe nanoparticles were chemically prepared using three different compositional regimes, viz., Cd rich, Se rich, and stoichiometric and were of different sizes in the range of 5-7 nm. The optical and the structural properties in the three cases were significantly different when the nanoparticles were subjected to natural oxidation. The CdSe nanoparticles were probed using Ar+ ion sputtering used in conjunction with X-Ray Photoelectron Spectroscopy for structural analysis, where as the optical studies were done using UV-VIS and the Photoluminescent measurements. The results showed a blue shift and a considerable decrease in the intensity associated to surface states (lambda approximately 600-700 nm) in case of Se rich case, no shift in stoichiometric CdSe suggesting that its stable against oxidation, and a red shift in PL position in Cd rich regime. The Stoke's shift observed in the nonstoichiometric cases can be associated with the quantum confinement and the stress/strain effects. The result demonstrate the role of Cd/Se stoichiometry in tuning the surface states for tailoring the desired optical properties.

The Cu2O nanoparticles having average crystallite diameters ∼8–16 nm were synthesized by a simple solvothermal method. The Mn was doped in the Cu2O sample of crystallite size ∼8 nm. The effects of the size and doping concentration on the crystal structures of the nanoparticles were investigated. The x-ray photoelectron spectroscopy studies clearly showed that the Mn was incorporated into the Cu2O lattice as Mn2+ due to the substitution of the Cu+ ions by Mn2+ ions. The quantum confinement effects were observed in the nanoparticles. The multiple emissions from the Cu2O were quenched in the Mn doped nanoparticles and only blue light emitting Cu2O nanoparticles were obtained due to the transition T42→A61 of Mn. The effects of the doping concentration and the particle size on the relaxations dynamics of the Cu2O nanoparticles were mainly investigated using photoluminescence decay.

This letter demonstrates the effect of cadmium selenide (CdSe) quantum dots on hole transport in poly(3-hexylthiophene) (P3HT) thin films. Current-voltage characteristics of P3HT and P3HT:CdSe thin films have been studied in the temperature range of 288–85K, in hole only device configurations, i.e., indium tin oxide (ITO)/poly(ethylene-dioxthiophene):polystyrenesulphonate (PEDOT:PSS)/P3HT/Au and ITO/PEDOT:PSS/P3HT:CdSe∕Au. The incorporation of CdSe quantum dots in P3HT results in the enhancement in hole current and switches the transport from dual conduction mechanism, viz., trap and mobility models to only trap model. This is attributed to the reduction in characteristic trap energy from 60to32meV and trap density from 2.5×1018to1.7×1018cm−3.