Ternary alloyed Cu2–xSySe1–y nanocrystals (NCs) were synthesized by using a simple and phosphine-free colloidal approach, in which sulfur powder and 1-dodecanethiol (DDT) were used as sulfur sources. In both cases, the crystal phase transformed from cubic berzelianite to monoclinic djurleite structure together with the morphology evolution from quasi-triangular to spherical or discal with an increase of sulfur content. Accordingly, the near-infrared (NIR) localized surface plasmon resonance (LSPR) absorption of the as-obtained sulfur-rich NCs exhibited obvious red-shift of wavelength and widening of absorption width. When the sulfur powder was chosen as sulfur sources, the LSPR wavelength of the as-obtained alloyed Cu2–xSySe1–y NCs could be tuned from 975 to 1230 nm with a decrease of selenium content in the NCs. In contrast, the region of the red-shift could be up to 1250 nm for the alloyed NCs synthesized by incorporation of different DDT dosage into the reaction system. The different sulfur sources and the electron donating effects of the DDT as a ligand played an important role in the LSPR absorption tuning. This deduction could be testified by the post-treating the quasi-triangular Cu2–xSe NCs with DDT under different temperatures and over different reaction time, which exhibited a red-shift of LSPR wavelength up to 450 nm due to coordination of DDT to Cu atoms on the NC surface while incorporating some sulfur anions into the lattice. This study offers a convenient tool for tuning the LSPR absorption of copper chalcogenide NCs and makes them for application in biological and optoelectronic fields.

•A microwave annealing method was proposed to prepare sol-gel ZnO films.•Enhanced performance was achieved in the BHJ-PSCs with ZnO (MW) ETLs.•ZnO (MW) ETLs contributed to the preferable interfacial contact in BHJ-PSCs.•The charge transport dynamics was investigated by a series of measurements.In this work, we propose a facile microwave-assisted approach for annealing sol-gel derived ZnO films to serve as electron transport layers (ETLs) for inverted bulk heterojunction polymer solar cells. We have demonstrated an impressive enhancement in performance for devices based on a poly (3-hexylthiophene) (P3HT): (6,6)-phenyl-C61-butyric acid methyl ester (PC61BM) system employing the microwave-annealed ZnO (ZnO (MW)) ETLs in comparison to the cases using the conventional hotplate-annealed ZnO (ZnO (HP)) ones. The better electron transport in the device with the ZnO (MW) ETL is mainly ascribed to the preferable interfacial contact as evidenced by the morphology characteristics. Furthermore, the comprehensive analyses conducted from the light intensity dependent photocurrent and photovoltage measurements, the capacitance-voltage characteristics, and the alternating current impedance spectra suggest that the utilization of the ZnO (MW) ETLs can effectively suppress trap-assisted recombination as well as charge accumulation at the interface between P3HT: PC61BM layers and ZnO layers, which is responsible for the enhanced device performance.

•White light-emitting diodes were fabricated based on cadmium-free Cu-In-Zn-S-based QDs and polymer via a simple solution-processed technique.•White electroluminescence was obtained under the annealing temperature of 95 °C.•The WLEDs exhibited a high CRI of 90 with a CIE coordinate of (0.33, 0.32).Bright white light-emitting diodes (WLEDs) were fabricated by using a simple solution-processed technique, in which the yellow cadmium-free Cu-In-Zn-S/ZnS core/shell quantum dots (QDs) blending with poly [(9, 9-dioctylfluorenyl-2, 7-diyl)-co-(4, 4′-(N-(p-butylphenyl)) diphenylamine)] (TFB) was used as emissive layers. The color of the electroluminescence (EL) from the device could be tuned from blue-green to white by varying the thermal annealing temperatures, and white EL emission could be obtained under the annealing temperature of 95 °C. A high color rendering index (CRI) of 90 and the Commission Internationale de l'Eclairage (CIE) color coordinates of (0.33, 0.32) were achieved in the WLEDs annealed at 95 °C, respectively. The WLEDs exhibited a low turn-on voltage of 2.5 V and a maximum luminance of 1500 cd/m2, which were maintained at 0.1 cd/A over a wide range of luminance from 100 to 1300 cd/m2. This work may open up a new way to realize white light in the planar WLEDs based on the cadmium-free QDs.Download high-res image (229KB)Download full-size image

Miniaturized channel filters are in high demand for many applications such as photonic integrated circuits, information-based technology, and platforms for investigation of light–matter interactions. Recently, several photonic schemes have been proposed to achieve nanofilters, which require sophisticated growth techniques. Here, we have fabricated microdisk whispering-gallery-mode (WGM) resonators through controlled assembly of organic materials with an emulsion-solvent-evaporation method. Based on this emulsion assembly method, the diameters of microdisks can be easily controlled, and more importantly, a microwire-disk interconnected structure is able to be constructed via one-step assembly. This microwire-waveguide-connected microdisk heterostructure can be utilized as a channel drop filter. Our results have demonstrated a facile way to achieve flexible WGM-based photonic components which can be integrated with other functional devices.Download high-res image (133KB)Download full-size imageThe microwire-disk interconnected structure have been fabricated via one-step assembly, which can be utilized as a channel drop filter.

Polymer/nanoparticle (NP) composite films have attracted great attention due to their potential applications in electrical bistable devices. The bistable mechanism is usually attributed to electron trapping and detrapping between the NP trap center and the polymer matrix. However, the exact conduction switching mechanism is still in controversy and even in the same polymer/NP system based devices the switch-on mechanism has been explained by two different models: either Fowler–Nordheim (FN) tunneling or trapped charge-limit-current (TCLC). Therefore, the study on the conduction switching mechanism for polymer/NP composite electrical bistable devices is critically necessary. In this work, ZnO NPs embedded in poly (ethylene oxide) (PEO) were first applied in electrical bistable devices using a solution process and the effect of the nanoparticle surface defects on the conduction switching mechanism is studied. The electrical bistability is observed from the device with the structure ITO/PEO : ZnO-NPs/Al and the conduction switch-on process is dependent on the existence of ZnO surface defects. The effect of the nanoparticle surface defects was investigated by current–voltage, Scanning Electron Microscopy (SEM), and photoluminescence measurements. Besides effectively separating nanoparticles, the surface capping can passivate the surface defects and affect the electrical hysteresis. The switch-on mechanism for the devices based on the NPs with surface detects can be modeled by TCLC while the one based on the NPs with the complete surface defect passivation can be explained by FN tunneling. The results demonstrate that the FN tunneling induced conduction switch-on process is more desirable in electrical bistable devices due to the better device performances.

A simple low-cost and phosphine-free colloidal method was developed to prepare disk-shaped Cu2−xS nanocrystals (NCs) with different crystal structures and basal planes, which could be manipulated effectively by varying the Cu:S feed molar ratios and the amount of surfactants. The near-infrared (NIR) localized surface plasmon resonance (LSPR) wavelength could be tuned from 1133 to 1512 nm with the crystal phase changing from CuS (covellite) to monoclinic Cu7S4 (roxbyite) and Cu31S16 (djurleite). Phase transformation had more important effects on tuning the plasmonic resonance than the surface interaction of the deprotonated carboxyl functional group of oleic acid. Moreover, the crystal phase could transform from covellite to djurleite and the morphology underwent a transition from nanodisks to nanospheres when the post-treatment temperature of CuS nanodisks by dodecanethiol (DDT) was increased to 120 °C, but only a size decrease took place at room temperature. As a result, a slight red-shift of the LSPR wavelength was observed at room temperature, but an obvious red-shift from 1140 to 1910 nm with the change in crystal structure and morphology. The post-treatment temperature played an important role in tuning the plasmonic resonance of the products, which was closely associated with the variation of the crystal structure, morphology and surface properties.

A series of different-shaped Cu31S16–metal sulfide (ZnS, CdS and CuInS2) heteronanostructures have been synthesized using a simple two-phase approach for the first time. This two-phase approach may shed light on the synthesis of Cu31S16-based heteronanostructures.

•Cadmium-free QLEDs were fabricated via a simple solution-processed technique.•The Cu-In-Zn-S/ZnS nanocrystals exhibited bright solid-state emission.•The cadmium-free QLEDs had a very low turn-on voltage and an improved performance.High-efficiency green, yellow and red quantum-dot light emitting devices (QLEDs) have been fabricated via a simple solution-processed technique, in which different-colored Cu-In-Zn-S/ZnS core/shell colloidal semiconductor nanocrystals (NCs) are used as emissive layers sandwiched between an organic holes transport layer and an electron transport layer of ZnO nanoparticles. The yellow QLEDs exhibit a low turn-on voltage of 1.8 V and high luminance of 3061 cd/m2 as well as the peak external quantum efficiency (EQE) of 2.42%. In contrast, the green and red QLEDs show a low turn-on voltage of 2 V, and their electroluminescence (EL) peaks are located at 540 and 642 nm with the peak EQE of 0.25% and 0.91%, respectively. The solution-processed high-efficiency cadmium-free QLEDs with a low turn-on voltage and good reproducibility may become one of the most promising next generation of display.

•A simple surfactant-assisted colloidal approach was employed to prepare highly luminescent organometal halide perovskite QDs.•The CH3NH3PbBr3 QDs exhibited strong size-dependent optical properties due to quantum confinement effects.•The emission color of the halide perovskite QDs could be tuned by changing the halogen elements.Size-tunable organometal halide perovskite CH3NH3PbBr3 quantum dots (QDs) were successfully synthesized by a simple surfactant-assisted reprecipitation technique, in which the size-tunability was realized by varying the molar ratios of methylammonium bromide (CH3NH3Br) to PbBr2 while the total amount of octylamine (OTAm) and CH3NH3Br remained unchanged. The diameters of CH3NH3PbBr3 QDs could be effectively tuned from 1.6 to 3.9 nm, and these QDs exhibited an obviously size-dependent optical properties, whose photoluminescence (PL) covered the spectral region from 440 to 530 nm and the emission width was 20–32 nm. The maximum absolute PL quantum yield (PLQY) was measured to be as high as approximately 80% at room temperature. A plausible formation mechanism was proposed and the quantum confinement effect was discussed based on effective mass approximation. Moreover, this synthetic approach could also be extended to prepare different halide perovskite QDs including CH3NH3PbClxBr3−x and CH3NH3PbBr3−x Ix (x = 1–3), which realized the color-tunability over the entire visible spectral region of 390–750 nm. The size- and compositional-tunable emission colors of organometal perovskite QDs endows them wide potential applications in next-generation optoelectronic devices.

•We theoretically investigated the fluorescence quenching in protic solvent.•We analyzed the effect of charge transfer on the quenching process.•The main method we used is relaxed scans.•The conical intersection was found in potential energy profiles.•The saddle point was found in potential energy surface.The fluorescence quenching of fluorenone in protic solvent has been extensively investigated, and the intermolecular hydrogen bond was found to play a crucial role. Unfortunately, the mechanism at atomic level is still not clear. In the present work, we theoretically put forward the charge transfer along the hydrogen bond in the excited states. The vertical excitation energies of the fluorenone-methanol complex as well as the potential energy profiles and surfaces of the vertical excited states and charge transfer states were calculated by using the ab initio electronic-structure methods. The photochemical reactions occurring in the diverse charge transfer states were compared and their decisiveness to the fluorescence quenching was discussed in the paper.

We demonstrate the use of TiO2 nanorods with well-controlled lengths as excellent electron extraction materials for significantly improving the performance of inverted polymer solar cells. The cells containing long nanorods outperform the devices using amorphous TiO2 particles as the electron extraction layer, mainly by a 2-fold increase in short-circuit current and fill factor. The enhanced charge extraction is attributed to the high electron mobility in crystalline nanorods and their preferential alignment during film formation. Furthermore, transient photocurrent studies suggest the presence of fewer interfacial and internal defects in the nanorod interlayers, which can effectively decrease carrier recombination and suppress electron trapping.

Colloidal djurleite nanocrystals exhibit a well-defined and strong localized surface plasmon resonance absorption in the near-infrared region, which arises from the excess free holes in the valence band. The near-infrared localized surface plasmon resonance absorption wavelength of the as-obtained djurleite nanocrystals can be modulated by varying their size and shape, which are controlled through the variation of the reaction conditions during the synthesis. For a given size, the plasmonic behavior of the spherical nanocrystals exhibits an obvious surface-dependent shift due to the different electron-donating abilities of the surface ligands, which leads to the change of hole density. Moreover, the plasmonic band of the djurleite nanocrystals shifts to a shorter wavelength upon exposure to air for longer time, during which no crystal structure is altered, and this blue-shift may be attributed to the increasing density of copper vacancies. The experimental results of the near-infrared plasmonic behavior are in good agreement with the calculated results based on the Mie–Drude model.

A simple heating-up colloidal approach has been developed to synthesize quaternary Cu–In–Zn–S (CIZS) nanocystals with different emission colors, which can be tuned by varying the Cu:In:Zn precursor ratios. The as-obtained products have a quasi-triangular shape with a small size distribution, and their crystal phase can be varied from cubic zinc-blende to hexagonal wurtzite structure with an increase of Cu stoichiometry. The inductively coupled plasma optical emission spectrometry (ICP-OES) results reveal that the as-obtained CIZS nanocrystals are Cu-deficient, and the Cu-vacancies have a significant effect on their optical properties. Moreover, the photoluminescence (PL) spectra of the CIZS nanocrystals recorded at different growth periods indicate that the partial cation exchange of Cu+ and In3+ with Zn2+ takes charge of the growth process. After coating a ZnS shell over the CIZS nanocrystals, the PL quantum yield (PLQY) is improved greatly and a blue-shift of the PL peak is observed as compared to that of plain CIZS nanocrystals. More interestingly, the highly luminescent CIZS/ZnS core/shell nanocrystals with different colors have been incorporated into poly(dimethylsiloxane) (PDMS) to be fabricated on an engraved “BJTU” glass substrate, and the as-obtained PDMS membranes exhibit a bright emission under UV light, which also show good stability when they are bent arbitrarily or immersed in water. This heating-up method has also been extended to the preparation of five-component Cu–Ag–In–Zn–S and Cu–Mn–In–Zn–S nanocrystals, which possess a cubic zinc-blende crystal structure and have bright luminescence. Our work may shed light on the synthesis of multi-component semiconductor nanocrystals.

●DIO solvent additive is not almighty for PCE improvement of PSCs.●Morphology of active layer can be effectively adjusted by DIO additive and ethanol treatment.●The PCE was decreased from 4.57% to 1.96% by adding DIO additive and recovered to 3.71% by ethanol treatment.Solvent additive 1,8-diiodooctane (DIO) is not almighty for improving the performance of polymer solar cells (PSCs). In this paper, the effect of solvent additive DIO and ethanol treatment on the performance of polymer solar cells (PSCs) with poly{[4,9-dihydro-4,4,9,9-tetra(4-hexylbenzyl)-s-indaceno[1,2-b:5,6-b′]-dithiophene-2,7-diyl]-alt-[2,3-bis(3-(octyloxy)phenyl)-2,3-dihydro-quinoxaline-2,2′-diyl] (PIDTDTQx) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the active layer was investigated. The power conversion efficiency (PCE) was decreased from 4.57% to 1.96% by adding 4 vol% DIO solvent additive for the active layer processed with 1,2-dichlorobenzene (DCB) as solvent. The negative effect of DIO on PCE from 1.94% to 1.18% of PSCs processed with chlorobenzene (CB) as solvent was further demonstrated. The PCE values of PSCs with DIO additive can be effectively increased from 1.96% to 3.71% for DCB as solvent and from 1.18% to 1.89% for CB as solvent by ethanol treatment on the active layer. The crystalline and morphology of active layers play the key role in determining the performance of PSCs.

A simple one-pot colloidal method has been described to engineer ternary CuInS2 nanocrystals with different crystal phases and morphologies, in which dodecanethiol is chosen as the sulfur source and the capping ligands. By a careful choice of the anions in the metal precursors and manipulation of the reaction conditions including the reactant molar ratios and the reaction temperature, CuInS2 nanocrystals with chalcopyrite, zincblende and wurtzite phases have been successfully synthesized. The type of anion in the metal precursors has been found to be essential for determining the crystal phase and morphology of the as-obtained CuInS2 nanocrystals. In particular, the presence of Cl− ions plays an important role in the formation of CuInS2 nanoplates with a wurtzite–zincblende polytypism structure. In addition, the molar ratios of Cu to In precursors have a significant effect on the crystal phase and morphology, and the intermediate Cu2S–CuInS2 heteronanostructures are formed which are critical for the anisotropic growth of CuInS2 nanocrystals. Furthermore, the optical absorption results of the as-obtained CuInS2 nanocrystals exhibit a strong dependence on the crystal phase and size.

•D/A intermolecular arrangement strongly determines OSCs performance.•Large VOC of 1.15 V was obtained for the OSCs based on ICBA as acceptor.•The champion PCE of 7.05% was obtained for the cells with PC71BM as acceptor.A series of solution processed organic solar cells (OSCs) were fabricated with a two-dimensional conjugated small molecule SMPV1 as electron donor and fullerene derivatives PC71BM or ICBA as electron acceptor. The champion power conversion efficiency (PCE) of OSCs arrives to 7.05% for the cells with PC71BM as electron acceptor. A relatively large open circuit voltage (VOC) of 1.15 V is obtained from cells using ICBA as electron acceptor with an acceptable PCE of 2.54%. The fill factor (FF) of OSCs is 72% or 61% for the cells with PC71BM or ICBA as electron acceptor, which is relatively high value for small molecule OSCs. The relatively low performance of OSCs with ICBA as electron acceptor indicates that ICBA cannot play positive role in photoelectric conversion processes, which is very similar to the phenomenon observed from the OSCs with high efficient narrow band gap polymers other than P3HT as electron donor, the underlying reason is still in debate. The SMPV1 has strong self-assemble ability to form an ordered two dimensional lamellar structure, which provides an effective platform to investigate the effect of electron acceptor chemical structure on the performance of OSCs. Experimental results exhibit that ICBA molecules may prefer to vertical cross-intercalation among side chains of SMPV1, PC71BM molecules may have better miscibility with SMPV1 in the active layer. The different donor/acceptor (D/A) intermolecular arrangement strongly influences photon harvesting, exciton dissociation and charge carrier transport, which may provide a new sight on performance improvement of OSCs by adjusting D/A intermolecular arrangements.

A series of Y1–xPO4:xTb3+ (x=0.005–0.1) phosphors were successfully fabricated by using co-precipitation method with NH4H2PO4 as phosphorus source. The structure and morphology characterization of the luminescent material was investigated with X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM). The XRD patterns indicated that the samples belonged to tetragonal phase. Luminescence properties were discussed by measuring the excitation and emission spectra. The phosphor could be excited by UV light (340–390 nm) and emitted green light, with the emission peaks located at 491 (5D4→7F6), 550 (5D4→7F5), 589 (5D4→7F4) and 624 nm (5D4→7F3). In addition, the pH value and activator concentration had great effects on the emission intensity. The results illuminated that this phosphor could be used for UV based white light emitting diodes and co-precipitation method could be used to prepare better appearance phosphor.The relation between emission spectra of YPO4:Tb3+ phosphors excited at 371 nm and pH values of reaction solution (pH=4, 5.5, 6.5 8.5, 9.5 and 11)

A novel white emitting phosphor Ca2PO4Cl:Dy3+ was synthesized by a solid state method. The luminescence, concentration quenching and thermal stability of Ca2PO4Cl:Dy3+ were investigated. Ca2PO4Cl:Dy3+ showed three emission peaks, which were located at 483, 575 and 660 nm. Though the ratio of yellow to blue emission intensities showed a similar value, the intensities of yellow and blue peaks were influenced by Dy3+ concentration, and the concentration quenching effect was observed. The emission intensity of Ca2PO4Cl:Dy3+ as a function of temperature was explored and the emission intensity (at 150 °C) of Ca2PO4Cl:Dy3+ was 90.0% of the value at 25 °C, and activation energy was 0.18 eV. The results indicated that Ca2PO4Cl:Dy3+ might be conducive to development of white LEDs.Emission (a), excitation (b) spectra of Ca2PO4Cl:0.05Dy3+ and transitions of Dy3+ (c)

A novel donor-acceptor (D-A) structural polymer PBDT-BTzQx-C12 consisting of benzodithiophene and triazoloquinoxaline units as donor and acceptor building blocks was synthesized. The PBDT-BTzQx-C12 was evaluated as complementary electron donor in polymer solar cells (PSCs) with poly(3-hexylthiophene) (P3HT) as electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as electron acceptor. The power conversion efficiencies (PCEs) of PSCs were improved from 3.18% to 3.54% by doping 2 wt. % PBDT-BTzQx-C12, corresponding to an approximately 11% PCE improvement. The performance improvement of ternary PSCs should be attributed to the increase of photon harvesting and the optimized phase separation of active layers by doping D-A structural PBDT-BTzQx-C12.

With Ar plasma treatment of the indium tin oxide (ITO) cathode, we achieve efficient inverted bulk heterojunction solar cells based on poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester, which do not require electron selective layer. The plasma treatment improves the power conversion efficiency of the device from 1.07% to 3.57% with a fill factor of 66%, open-circuit voltage of 0.60 V, and short-circuit current of 9.03 mA cm−2. This result is comparable to the regular inverted devices with an additional electron selective layer. The Kelvin probe detects a reduction in the ITO work function of ∼0.45 eV after plasma treatment, which finally leads to an increase in the built-in potential and faster carrier extraction. As a result, good device performance is achieved. Because the electron selective layer becomes unnecessary, our strategy suggests a simple way to achieve efficient inverted organic solar cells.

We present a route to successfully tackle the two main limitations, low open circuit voltage (Voc) and limited short circuit-density (Jsc), of polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) as an electron-donor. The indene-C60 bisadduct (ICBA) was selected as an electron acceptor to improve the open circuit voltage (Voc). The narrow band gap polymer poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b′]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl] (PBDTTT-C), as a complementary electron-donor material, was doped into the host system of P3HT:ICBA to form ternary cascade energy structured PSCs with increased Jsc. The power conversion efficiency (PCE) of P3HT:ICBA-based cells was improved from 3.32% to 4.38% by doping with 3 wt% PBDTTT-C with 1 min 150 °C annealing treatment. The 4.38% PCE of ternary PSCs is still larger than the 3.79% PCE of PSCs based on P3HT:ICBA with 10 minutes 150 °C annealing treatment.

High-quality rhombohedral digenite (Cu1.8S) nanocrystals (NCs) were synthesized using a facile one-pot approach, in which foreign metal ions (Zn2+ and Cd2+) were added to drive a transformation in the phase and morphology of the as-obtained Cu2−xS NCs. During this process, the as-obtained products could transform from monoclinic djurleite (Cu1.94S) NCs to rhombohedral Cu1.8S NCs in the presence of Zn2+ and Cd2+ ions by extending the reaction time and increasing the reaction temperature, which could provide sufficient energy to overcome activation energy barriers. Moreover, we further studied the evolution of the plasmonic properties of the as-obtained Cu2−xS NCs, and the near-infrared (NIR) localized surface plasmon resonance (LSPR) absorption wavelength could be tuned by varying the amount of Zn2+ and Cd2+ ions added into the reaction system, which was in close association with the change in copper deficiencies and free hole densities induced by foreign metal ions.

Cu2−xS nanocrystals with different morphologies and crystal phases have been synthesized by using a simple one-pot and phosphine-free colloidal method, in which different alkanethiols (CnH2n+1SH, n = 8, 12, 18) have been selected as sulfur sources and capping ligands. The crystal phase can be transformed from monoclinic Cu1.94S to tetragonal Cu1.81S by varying the alkyl chain length of alkanethiols, and the morphology changes from nanospheres to nanodisks during the phase transformation. Strong localized surface plasmon resonance (LSPR) absorbance in the near-infrared (NIR) region has been observed in these Cu2−xS nanocrystals, which originates from excess holes in the valence band due to copper deficiencies. The alkyl chain length of alkanethiols plays an important role in the crystal phase, morphology and plasmonic properties of the as-obtained Cu2−xS nanocrystals.

•The electrochemical reduction of nanocrystals is conducted in aqueous electrolyte.•The degradation of nanocrystals is avoided by fast scan in the redox process.•The fast charge transfer process on electrode indicates DNA–CTMA is conducting.The electrochemical redox behaviors of Cu(I) doped CdS nanoparticles in DNA–CTMA films are investigated in aqueous electrolyte. Both oxidation and reduction processes are electrochemically irreversible. The degradation of nanoparticles and the coupled chemical reactions in the electrochemical measurements can be avoided by fast potential scan as 1.5 V s−1. It is hardly found the residual O2 effect on the redox behavior of nanoparticles in DNA–CTMA film. The role of DNA–CTMA matrix in the charge transfer process between nanoparticles and the electrode is discussed.

•We investigated six small organic molecules by using computational approaches.•This investigation is mainly based on the Marcus electron transfer theory.•The density functional theory (DFT) was used in this investigation.•The IP, EA, reorganization energy and transfer integral were calculated.•We analyzed the charge properties of the molecules by using the computed results.The charge injection and transport properties of six organic light-emitting molecules with push–pull structures were studied by theoretical calculations. The ground-state geometries for the neutral, cationic and anionic states were optimized using density functional theory. Subsequently, the ionization potentials and electron affinities were calculated. We computed the reorganization energies and the transfer integrals based on the Marcus electron transfer theory. It was found that in addition to being emitters the six compounds are multifunctional materials being capable of transport for both holes and electrons. Moreover, the double-branched compound DCDPC2 was found to have higher charge injection ability and better balanced charge transport properties than single-branched compounds.Graphical abstract

In this study, large-sized silver nanoparticles (Ag NPs) (average size: 80 nm) have been introduced into the anodic buffer poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer (thickness: about 55 nm) of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester bulk heterojunction polymer solar cells. The results showed that the short-circuit current density can increase from 8.73 to 11.36 mA/cm2, and power conversion efficiency increases from 2.28 to 2.65 % when 0.1 wt% Ag NPs was incorporated in PEDOT:PSS layer, corresponding to an efficiency improvement of 16.2 %. Absorption spectrums of the active layers indicate that large-sized Ag NPs have no clear contribution to optical absorption improvement. By measuring the conductivity of PEDOT:PSS films without and with Ag NPs and analyzing device structure of this polymer solar cell, it was founded that the improvements in power conversion efficiency was originated from higher conductivity of PEDOT:PSS layer incorporated with Ag NPs and the shorter routes for holes to travel to the anode.

The frontier orbitals, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, of organic dye (5-(4-(di-p-tolylamino)-phenyl)-4-hexylthiophen-2-yl)-2-cyanoacrylic acid (TT) and (5-(5-(4-(di-p-tolylamino)-phenyl)-4-hexylthiophen-2-yl-methylene)-4-oxo-2-thioxothiazolidin-3-yl)-acetic acid (TS) are evaluated by the electrochemical cyclic voltammetry in aqueous electrolyte. Both dyes are electrochemically active and conduct redox processes when the dyes are blended with DNA–CTMA(DNA-cetyltrimethylammonium). The redox processes of the dyes can be carried out under fast potential scanning, e.g. 1.5 V/s, which indicates the fast charge transfer between the dyes and the electrodes. Well-dispersed dye molecules in DNA–CTMA, rather than the aggregated molecules, result in well-defined redox peaks in the cyclic voltammetry. In addition, the conductive DNA is also proposed to be responsible for the fast charge transfer. HOMO and LUMO levels of TT and TS are −5.40 eV and −3.04 eV for TT, −5.42 eV and −3.40 eV for TS, respectively.

A facile one-pot heating process without any injection has been developed to synthesize different Cu–Zn–S-based nanocrystals. The composition of the products evolves from Cu(I)-doped ZnS (ZnS:Cu(I)) nanocrystals into heterostructured nanocrystals consisting of monoclinic Cu1.94S and wurtzite ZnS just by controlling the molar ratios of zinc acetylacetonate (Zn(acac)2) to copper acetylacetonate (Cu(acac)2) in the mixture of n-dodecanethiol (DDT) and 1-octadecene (ODE). Accompanying the composition transformation, the crystal phase of ZnS is changed from cubic zinc blende to hexagonal wurtzite. Depending on the synthetic parameters including the reaction time, temperature, and the feeding ratios of Zn/Cu precursors, the morphology of the as-obtained heterostructured nanocrystals can be controlled in the forms of taper-like, matchstick-like, tadpole-like, or rod-like. Interestingly, when the molar ratio of Cu(acac)2 to Zn(acac)2 is increased to 9:1, the crystal phase of the products is transformed from monoclinic Cu1.94S to the mixed phase composed of cubic Cu1.8S and tetragonal Cu1.81S as the reaction time is further prolonged. The crystal-phase transformation results in the morphological change from quasi-spherical to rice shape due to the incorporation of Zn ions into the Cu1.94S matrix. This method provides a simple but highly reproducible approach for synthesis of Cu(I)-doped nanocrystals and heterostructured nanocrystals, which are potentially useful in the fabrication of optoelectronic devices.

A one-step colloidal process was adopted to prepare face-centered-cubic PbS nanocrystals with different shapes such as octahedral, starlike, cubic, truncated octahedral, and truncated cubic. The features of this approach avoid the presynthesis of any organometallic precursor and the injection of a toxic phosphine agent. A layered intermediate compound (lead thiolate) forms in the initial stage of the reaction, which effectively acts as the precursor to decompose into the PbS nanocrystals. The size and shape of the PbS nanocrystals can be easily controlled by varying the reaction time, the reactant concentrations, the reaction temperatures, and the amount of surfactants. In particular, additional surfactants other than dodecanethiol, such as oleylamine, oleic acid, and octadecene, play an important role in the shape control of the products. The possible formation mechanism for the PbS nanocrystals with various shapes is presented on the basis of the different growth directions of the nanocrystals with the assistance of the different surfactants. This method provides a facile, low-cost, highly reproducible process for the synthesis of PbS nanocrystals that may have potential applications in the fabrication of photovoltaic devices and photodetectors.

High-quality spherical silver (Ag) nanocrystals have been synthesized by using a one-pot approach, in which pre-synthesis of organometallic precursors is not required. This reaction involves the thermolysis of a mixed solution of silver acetate and n-dodecanethiol in a non-coordinating organic solvent. The size of the as-obtained Ag nanospheres can be controlled by adjusting the reaction time, reaction temperature and the amount of silver acetate added. The growth and nucleation process of the resultant Ag nanospheres have been studied by employing UV–vis absorption spectra and transmission electron microscopy (TEM) images. Furthermore, these Ag nanospheres have good self-assembly behaviors, and they are easily self-assembled into two- or three-dimensional superlattice structures due to the bundling and interdigitation of thiolate molecules adsorbed on Ag nanospheres. This one-pot synthetic procedure is simple and highly reproducible, which may be extended to prepare other noble-metal nanocrystals.Graphical abstractDifferent sized and monodisperse silver nanospheres were prepared using a one-pot approach with no pre-synthesis of organometallic precursors, and the silver nanospheres can self-assemble into highly ordered superlattices.Highlights► Monodisperse silver nanospheres have been synthesized by a one-pot approach. ► The synthetic method does not need pre-synthesis of organometallic precursors. ► The silver nanospheres can self-assemble into highly ordered superlattices. ► This synthetic method can be extended to prepare other metal nanocrystals.

We report the electrical bistability of cadmium sulfide (CdS) nanoparticles (NPs) capped by dodecanethiol, which are sandwiched between aluminum tris (8-hydroxyquinoline) (Alq3) layers. The current density–voltage (J–V) characteristics of the device with Al/Alq3/CdS NPs/Alq3/Al structures show the high- and low-conducting state at the same voltage, and the two states are reproducible by applying different negative sweeping voltages. The Ohmic model and the space–charge limited model are proposed and supported by the current density–voltage results, which give a possible transport mechanism for the electrical bistability of our devices.

We present a route to successfully tackle the two main limitations, low open circuit voltage (Voc) and limited short circuit-density (Jsc), of polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) as an electron-donor. The indene-C60 bisadduct (ICBA) was selected as an electron acceptor to improve the open circuit voltage (Voc). The narrow band gap polymer poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b′]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl] (PBDTTT-C), as a complementary electron-donor material, was doped into the host system of P3HT:ICBA to form ternary cascade energy structured PSCs with increased Jsc. The power conversion efficiency (PCE) of P3HT:ICBA-based cells was improved from 3.32% to 4.38% by doping with 3 wt% PBDTTT-C with 1 min 150 °C annealing treatment. The 4.38% PCE of ternary PSCs is still larger than the 3.79% PCE of PSCs based on P3HT:ICBA with 10 minutes 150 °C annealing treatment.

A series of different-shaped Cu31S16–metal sulfide (ZnS, CdS and CuInS2) heteronanostructures have been synthesized using a simple two-phase approach for the first time. This two-phase approach may shed light on the synthesis of Cu31S16-based heteronanostructures.

A simple low-cost and phosphine-free colloidal method was developed to prepare disk-shaped Cu2−xS nanocrystals (NCs) with different crystal structures and basal planes, which could be manipulated effectively by varying the Cu:S feed molar ratios and the amount of surfactants. The near-infrared (NIR) localized surface plasmon resonance (LSPR) wavelength could be tuned from 1133 to 1512 nm with the crystal phase changing from CuS (covellite) to monoclinic Cu7S4 (roxbyite) and Cu31S16 (djurleite). Phase transformation had more important effects on tuning the plasmonic resonance than the surface interaction of the deprotonated carboxyl functional group of oleic acid. Moreover, the crystal phase could transform from covellite to djurleite and the morphology underwent a transition from nanodisks to nanospheres when the post-treatment temperature of CuS nanodisks by dodecanethiol (DDT) was increased to 120 °C, but only a size decrease took place at room temperature. As a result, a slight red-shift of the LSPR wavelength was observed at room temperature, but an obvious red-shift from 1140 to 1910 nm with the change in crystal structure and morphology. The post-treatment temperature played an important role in tuning the plasmonic resonance of the products, which was closely associated with the variation of the crystal structure, morphology and surface properties.

A simple heating-up colloidal approach has been developed to synthesize quaternary Cu–In–Zn–S (CIZS) nanocystals with different emission colors, which can be tuned by varying the Cu:In:Zn precursor ratios. The as-obtained products have a quasi-triangular shape with a small size distribution, and their crystal phase can be varied from cubic zinc-blende to hexagonal wurtzite structure with an increase of Cu stoichiometry. The inductively coupled plasma optical emission spectrometry (ICP-OES) results reveal that the as-obtained CIZS nanocrystals are Cu-deficient, and the Cu-vacancies have a significant effect on their optical properties. Moreover, the photoluminescence (PL) spectra of the CIZS nanocrystals recorded at different growth periods indicate that the partial cation exchange of Cu+ and In3+ with Zn2+ takes charge of the growth process. After coating a ZnS shell over the CIZS nanocrystals, the PL quantum yield (PLQY) is improved greatly and a blue-shift of the PL peak is observed as compared to that of plain CIZS nanocrystals. More interestingly, the highly luminescent CIZS/ZnS core/shell nanocrystals with different colors have been incorporated into poly(dimethylsiloxane) (PDMS) to be fabricated on an engraved “BJTU” glass substrate, and the as-obtained PDMS membranes exhibit a bright emission under UV light, which also show good stability when they are bent arbitrarily or immersed in water. This heating-up method has also been extended to the preparation of five-component Cu–Ag–In–Zn–S and Cu–Mn–In–Zn–S nanocrystals, which possess a cubic zinc-blende crystal structure and have bright luminescence. Our work may shed light on the synthesis of multi-component semiconductor nanocrystals.

With Ar plasma treatment of the indium tin oxide (ITO) cathode, we achieve efficient inverted bulk heterojunction solar cells based on poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester, which do not require electron selective layer. The plasma treatment improves the power conversion efficiency of the device from 1.07% to 3.57% with a fill factor of 66%, open-circuit voltage of 0.60 V, and short-circuit current of 9.03 mA cm−2. This result is comparable to the regular inverted devices with an additional electron selective layer. The Kelvin probe detects a reduction in the ITO work function of ∼0.45 eV after plasma treatment, which finally leads to an increase in the built-in potential and faster carrier extraction. As a result, good device performance is achieved. Because the electron selective layer becomes unnecessary, our strategy suggests a simple way to achieve efficient inverted organic solar cells.

Colloidal djurleite nanocrystals exhibit a well-defined and strong localized surface plasmon resonance absorption in the near-infrared region, which arises from the excess free holes in the valence band. The near-infrared localized surface plasmon resonance absorption wavelength of the as-obtained djurleite nanocrystals can be modulated by varying their size and shape, which are controlled through the variation of the reaction conditions during the synthesis. For a given size, the plasmonic behavior of the spherical nanocrystals exhibits an obvious surface-dependent shift due to the different electron-donating abilities of the surface ligands, which leads to the change of hole density. Moreover, the plasmonic band of the djurleite nanocrystals shifts to a shorter wavelength upon exposure to air for longer time, during which no crystal structure is altered, and this blue-shift may be attributed to the increasing density of copper vacancies. The experimental results of the near-infrared plasmonic behavior are in good agreement with the calculated results based on the Mie–Drude model.

A simple one-pot colloidal method has been described to engineer ternary CuInS2 nanocrystals with different crystal phases and morphologies, in which dodecanethiol is chosen as the sulfur source and the capping ligands. By a careful choice of the anions in the metal precursors and manipulation of the reaction conditions including the reactant molar ratios and the reaction temperature, CuInS2 nanocrystals with chalcopyrite, zincblende and wurtzite phases have been successfully synthesized. The type of anion in the metal precursors has been found to be essential for determining the crystal phase and morphology of the as-obtained CuInS2 nanocrystals. In particular, the presence of Cl− ions plays an important role in the formation of CuInS2 nanoplates with a wurtzite–zincblende polytypism structure. In addition, the molar ratios of Cu to In precursors have a significant effect on the crystal phase and morphology, and the intermediate Cu2S–CuInS2 heteronanostructures are formed which are critical for the anisotropic growth of CuInS2 nanocrystals. Furthermore, the optical absorption results of the as-obtained CuInS2 nanocrystals exhibit a strong dependence on the crystal phase and size.