Open structure ZnO/CdSe core/shell nanoneedle arrays for solar cells

Open structure ZnO/CdSe core/shell nanoneedle arrays were prepared on a conducting glass (SnO₂:F) substrate by solution deposition and electrochemical techniques. A uniform CdSe shell layer with a grain size of approximately several tens of nanometers was formed on the surface of ZnO nanoneedle cores after annealing at 400°C for 1.5 h. Fabricated solar cells based on these nanostructures exhibited a high short-circuit current density of about 10.5 mA/cm² and an overall power conversion efficiency of 1.07% with solar illumination of 100 mW/cm². Incident photo-to-current conversion efficiencies higher than 75% were also obtained.     

Optical simulations of P3HT/Si nanowire array hybrid solar cells

An optical simulation of poly(3-hexylthiophene) (P3HT)/Si nanowire array (NWA) hybrid solar cells was investigated to evaluate the optical design requirements of the system by using finite-difference time-domain (FDTD) method. Steady improvement of light absorption was obtained with increased P3HT coating shell thickness from 0 to 80 nm on Si NWA. Further increasing the thickness caused dramatic decrease of the light absorption. Combined with the analysis of ultimate photocurrents, an optimum geometric structure with a coating P3HT thickness of 80 nm was proposed. At this structure, the hybrid solar cells show the most efficient light absorption. The optimization of the geometric structure and further understanding of the optical characteristics may contribute to the development for the practical experiment of the promising hybrid solar cells.     

Ultraviolet-ozone-treated PEDOT:PSS as anode buffer layer for organic solar cells

ABSTRACT: Ultraviolet-ozone-treated poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)was used as the anode buffer layer in copper phthalocyanine (CuPc)/fullerene-based solar cells. The power conversion efficiency of the cells with appropriated UV-ozone treatment was found to increase about 20% compared to the reference cell. The improved performance is attributed to the increased work function of the PEDOT:PSS layer, which improves the contact condition between PEDOT:PSS and CuPc, hence increasing the extraction efficiency of the photogenerated holes and decreasing the recombination probability of holes and electrons in the active organic layers.     

Growth and characterization of ZnO/ZnTe core/shell nanowire arrays on transparent conducting oxide glass substrates

ABSTRACT: We report the growth and characterization of ZnO/ZnTe core/shell nanowire arrays on indium tin oxide. Coating of the ZnTe layer on well-aligned vertical ZnO nanowires has been demonstrated by scanning electron microscope, tunneling electron microscope, X-ray diffraction pattern, photoluminescence, and transmission studies. The ZnO/ZnTe core/shell nanowire arrays were then used as the active layer and carrier transport medium to fabricate a photovoltaic device. The enhanced photocurrent and faster response observed in ZnO/ZnTe, together with the quenching of the UV emission in the PL spectra, indicate that carrier separation in this structure plays an important role in determining their optical response. The results also indicate that core/shell structures can be made into useful photovoltaic devices.     

a-Si:H/SiNW shell/core for SiNW solar cell applications

Vertically aligned silicon nanowires have been synthesized by the chemical etching of silicon wafers. The influence of a hydrogenated amorphous silicon (a-Si:H) layer (shell) on top of a silicon nanowire (SiNW) solar cell has been investigated. The optical properties of a-Si:H/SiNWs and SiNWs are examined in terms of optical reflection and absorption properties. In the presence of the a-Si:H shell, 5.2% reflection ratio in the spectral range (250 to 1,000 nm) is achieved with a superior absorption property with an average over 87% of the incident light. In addition, the characteristics of the solar cell have been significantly improved, which exhibits higher open-circuit voltage, short-circuit current, and efficiency by more than 15%, 12%, and 37%, respectively, compared with planar SiNW solar cells. Based on the current–voltage measurements and morphology results, we show that the a-Si:H shell can passivate the defects generated by wet etching processes.     

n-ZnO/p-Si 3D heterojunction solar cells in Si holey arrays

A wafer-scale, low-cost solar cell based on n-ZnO/p-Si 3D heterojunction arrays on holey Si substrates has been fabricated. This device shows a power-conversion efficiency of 1.2% and high photosensitivity. The present n-ZnO/p-Si heterojunction architectures are envisaged as potentially valuable candidates for next-generation photovoltaics.     

Electrical properties of nitric acid and DMSO treated PEDOT:PSS/n-Si hybrid heterostructures for optoelectronic applications

Organic/inorganic heterostructures are an emerging and interesting field of research for optoelectronics. In this work, an efficient organic/inorganic hybrid heterojunction between PEDOT:PSS and n-type Silicon has been fabricated for optoelectronic applications. Samples with varying thickness of PEDOT:PSS were prepared by spin coating technique and the electrical conductivity of organic layers was modified using DMSO as additive. Post fabrication, the hybrid heterostructures were treated with HNO₃ vapor so as to enhance the conductivity of the organic layer. Surface treatment with HNO₃ was found to lower the roughness of the organic layer and enhance the transparency of the layer. I–V characteristics reveal optimized behavior of HNO₃ treated PEDOT:PSS layer with a low Ideality factor (n~3.2) and a barrier height (Φ_B) of 0.8 eV. The findings of the study provide a promising efficient method to enhance the electrical and device properties of PEDOT:PSS/n-Si heterostructures for optoelectronic applications. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48952.     

Electrodeposition of CdSe coatings on ZnO nanowire arrays for extremely thin absorber solar cells

We report on electrodeposition of CdSe coatings onto ZnO nanowire arrays and determine the effect of processing conditions on material properties such as morphology and microstructure. CdSe-coated ZnO nanowire arrays have potential use in extremely thin absorber (ETA) solar cells, where CdSe absorbs visible light and injects photoexcited electrons into the ZnO nanowires. We show that room-temperature electrodeposition enables growth of CdSe coatings that are highly crystalline, uniform, and conformal with precise control over thickness and microstructure. X-ray diffraction and transmission electron microscopy show nanocrystalline CdSe in both hexagonal and cubic phases with grain size ∼5 nm. Coating morphology depends on electrodeposition current density. Uniform and conformal coatings were achieved using moderate current densities of ∼2 mA cm⁻² for nanowires with roughness factor of ∼10, while lower current densities resulted in sparse nucleation and growth of larger, isolated islands. Electrodeposition charge density controls the thickness of the CdSe coating, which was exploited to investigate the evolution of the morphology at early stages of nucleation and growth. UV–vis transmission spectroscopy and photoelectrochemical solar cell measurements demonstrate that CdSe effectively sensitizes ZnO nanowires to visible light.     

In situ-prepared composite materials of PEDOT: PSS buffer layer-metal nanoparticles and their application to organic solar cells

We report an enhancement in the efficiency of organic solar cells via the incorporation of gold (Au) or silver (Ag) nanoparticles (NPs) in the hole-transporting buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which was formed on an indium tin oxide (ITO) surface by the spin-coating of PEDOT:PSS-Au or Ag NPs composite solution. The composite solution was synthesized by a simple in situ preparation method which involved the reduction of chloroauric acid (HAuCl₄) or silver nitrate (AgNO₃) with sodium borohydride (NaBH₄) solution in the presence of aqueous PEDOT:PSS media. The NPs were well dispersed in the PEDOT:PSS media and showed a characteristic absorption peak due to the surface plasmon resonance effect. Organic solar cells with the structure of ITO/PEDOT:PSS-Au, Ag NPs/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/LiF/Al exhibited an 8% improvement in their power conversion efficiency mainly due to the enlarged surface roughness of the PEDOT:PSS, which lead to an improvement in the charge collection and ultimately improvements in the short-circuit current density and fill factor.     

Improved photovoltaic performance of silicon nanowire/organic hybrid solar cells by incorporating silver nanoparticles

Silicon nanowire (SiNW) arrays show an excellent light-trapping characteristic and high mobility for carriers. Surface plasmon resonance of silver nanoparticles (AgNPs) can be used to increase light scattering and absorption in solar cells. We fabricated a new kind of SiNW/organic hybrid solar cell by introducing AgNPs. Reflection spectra confirm the improved light scattering of AgNP-decorated SiNW arrays. A double-junction tandem structure was designed to manufacture our hybrid cells. Both short-circuit current and external quantum efficiency measurements show an enhancement in optical absorption of organic layer, especially at lower wavelengths.     

Controllable synthesis of branched ZnO/Si nanowire arrays with hierarchical structure

A rational approach for creating branched ZnO/Si nanowire arrays with hierarchical structure was developed based on a combination of three simple and cost-effective synthesis pathways. The crucial procedure included growth of crystalline Si nanowire arrays as backbones by chemical etching of Si substrates, deposition of ZnO thin film as a seed layer by magnetron sputtering, and fabrication of ZnO nanowire arrays as branches by hydrothermal growth. The successful synthesis of ZnO/Si heterogeneous nanostructures was confirmed by morphologic, structural, and optical characterizations. The roles of key experimental parameters, such as the etchant solution, the substrate direction, and the seed layer on the hierarchical nanostructure formation, were systematically investigated. It was demonstrated that an etchant solution with an appropriate redox potential of the oxidant was crucial for a moderate etching speed to achieve a well-aligned Si nanowire array with solid and round surface. Meanwhile, the presence of gravity gradient was a key issue for the growth of branched ZnO nanowire arrays. The substrate should be placed vertically or facedown in contrast to the solution surface during the hydrothermal growth. Otherwise, only the condensation of the ZnO nanoparticles took place in a form of film on the substrate surface. The seed layer played another important role in the growth of ZnO nanowire arrays, as it provided nucleation sites and determined the growing direction and density of the nanowire arrays for reducing the thermodynamic barrier. The results of this study might provide insight on the synthesis of hierarchical three-dimensional nanostructure materials and offer an approach for the development of complex devices and advanced applications.     

Investigations on performance of PEDOT:PSS/V2O5 hybrid symmetric supercapacitor with redox electrolyte

Nanocomposites of PEDOT:PSS with V₂O₅ nanoparticles are synthesized by simple physical mixing of the two with different weight percentages of the latter and their performance as supercapacitor electrode materials is verified. Best performance is obtained for an optimum weight percent of 16.8% of V₂O₅. The specific capacitance and specific energy of the composite with 16.8% V₂O₅ increases by more than two fold, with increase in specific power, as compared to that of pristine PEDOT:PSS device. This is attributed to increase in conductivity brought about by the presence of V₂O₅ nanoparticles, easier transportation and intimate contact of electrolyte ions with the nanolayers of V₂O₅ due to the intercalation of PEDOT:PSS between the layers, and additional redox reactions due to various oxidation states of vanadium element, besides redox electrolyte effects. This is further confirmed by the reduced ESR of the composite device as compared to that of pristine PEDOT:PSS device.     

Humidity Sensor Based on PEO/PEDOT:PSS Blends for Breath Monitoring

The discrimination of humidity in exhaled breath is of utmost importance to turn breath analysis into an efficient noninvasive tool for early diagnosis or treatment monitoring of several diseases. Herein, by assembling different ratios of the conductive poly(3,4-ethylenedioxythiophene): polystyrene sulfonate with the polymer matrix polyethylene oxide (PEO), humidity chemiresistor-based sensors are designed and investigated. The testing results display a broad relative humidity detection range (6–92%), repeatability, reproducibility, and good reversibility. Meanwhile, the sensors possess good reliability for distinct temperatures and in the presence of typical volatile organic compounds found in human exhaled air. The hygroscopic idiosyncrasy of PEO is attributed to be the main responsible for the high sensibility toward humidity. In a proof-of-principle for detection of respiration humidity, the outcome shows the ability of the chemiresistors to detect the humidity variation in a real case of breath exposure up to 2 s intervals. The 30 d trial of stability readings shows a standard deviation of only 2.6%. These sensing devices appear as a new array component able to distinguish moisture from biomarkers of diagnosed diseases in breath analysis.     

Fabrication of morphology controllable rutile TiO2 nanowire arrays by solvothermal route for dye-sensitized solar cells

Highly ordered, vertically oriented TiO₂ nanowire arrays (TNAs) are synthesized directly on transparent conducting substrate by solvothermal procedure without any template. The X-ray diffraction (XRD) pattern shows that TiO₂ array is in rutile phase growing along the (0 0 2) direction. The field-emission scanning electron microscopy (FE-SEM) images of the samples indicate that the TiO₂ array surface morphology and orientation are highly dependent on the synthesis conditions. In a typical condition of solvothermal at 180 °C for 2 h, the TNAs are composed of nanowires 10 ± 2 nm in width, and several nanowires bunch together to form a larger secondary structure of 60 ± 10 nm wide. Dye-sensitized solar cell (DSSC) assembled with the TNAs grown on the FTO glass as photoanode under illumination of simulated AM 1.5G solar light (100 mW cm⁻²) achieves an overall photoelectric conversion efficiency of 1.64%.     

Synthesis and magneto-transport properties of single PEDOT/Ni and PEDOT/Ni30Fe70 core/shell nanowires

Single polyethylenedioxythiophene (PEDOT) nanowires bridging pairs of electrodes were utilized as positive templates to create PEDOT/Ni and PEDOT/Ni₃₀Fe₇₀ core/shell nanowires by electrodepositing ferromagnetic material (i.e., Ni and Ni₃₀Fe₇₀) on the entire assembly, including both the electrodes and nanowire. The temperature dependence of the electrical resistance indicated that electrons are transported predominately through the ferromagnetic shell. The magnetoresistive (MR) behavior of the core/shell nanowires was investigated as a function of temperature, magnetic field orientation, shell thickness, and composition. The MR behavior of the PEDOT/Ni core/shell nanowires was anomalous for low applied magnetic fields, deviating from expected anisotropic magnetoresistance, with positive ΔR/R_O values for all field orientations. PEDOT/Ni₃₀Fe₇₀ core/shell nanowires displayed the opposite behavior, with negative ΔR/R_O for both longitudinal and transverse field orientations. The origin of this magnetoresistive behavior is postulated to be a geometry induced domain wall effect.     

Improvement of the physical properties of ZnO/CdTe core-shell nanowire arrays by CdCl2 heat treatment for solar cells

CdTe is an important compound semiconductor for solar cells, and its use in nanowire-based heterostructures may become a critical requirement, owing to the potential scarcity of tellurium. The effects of the CdCl₂ heat treatment are investigated on the physical properties of vertically aligned ZnO/CdTe core-shell nanowire arrays grown by combining chemical bath deposition with close space sublimation. It is found that recrystallization phenomena are induced by the CdCl₂ heat treatment in the CdTe shell composed of nanograins: its crystallinity is improved while grain growth and texture randomization occur. The presence of a tellurium crystalline phase that may decorate grain boundaries is also revealed. The CdCl₂ heat treatment further favors the chlorine doping of the CdTe shell with the formation of chlorine A-centers and can result in the passivation of grain boundaries. The absorption properties of ZnO/CdTe core-shell nanowire arrays are highly efficient, and more than 80% of the incident light can be absorbed in the spectral range of the solar irradiance. The resulting photovoltaic properties of solar cells made from ZnO/CdTe core-shell nanowire arrays covered with CuSCN/Au back-side contact are also improved after the CdCl₂ heat treatment. However, recombination and trap phenomena are expected to operate, and the collection of the holes that are mainly photo-generated in the CdTe shell from the CuSCN/Au back-side contact is presumably identified as the main critical point in these solar cells.     

MXene Reinforced PAA/PEDOT:PSS/MXene Conductive Hydrogel for Highly Sensitive Strain Sensors

Conductive hydrogel has a vital application prospect in flexible electronic fields such as electronic skin and force sensors. Developing conductive hydrogel with significant toughness and high sensitivity is urgently needed for application research. In this work, a strong and sensitive strain sensor based on conductive hydrogel is demonstrated by introducing MXene (Ti3C2Tx) into the micelle crosslinked polyacrylic acid (PAA)/poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) hydrogel network. The functional polymer micelle crosslinkers can dissipate external stress by deformation, endowing the hydrogel with high strength. The combination of MXene both improves the polymer network structure and the conductive pathways, further enhancing the mechanical properties and sensing performance. Resultantly, the flexible strain sensor base on PAA/PEDOT:PSS/MXene conductive hydrogel exhibits excellent sensing performance with a high gauge factor of 20.86, a large strain detection range of 1000%, as well as good adhesion on different interfaces. Thus, it can be used to monitor various movements of the human body and identify all kinds of handwriting, showing great potential into wearable electronics.     

Block copolymer grafted-silica particles: a core/double shell hybrid inorganic/organic material

Hybrid inorganic/organic materials consisting of a poly(n-butyl acrylate)-b-poly(styrene) diblock copolymer anchored to silica particles were synthesized via ‘grafting from’ technique using a controlled/living free radical polymerization named stable free radical polymerization. XPS and FTIR analysis were used to control the effectiveness of the chemical modification of the silica particles. Thermal characterizations were performed by thermal gravimetric analysis (TGA) and by differential scattering calorimetry (DSC). The TGA permitted the determination of the quantity of grafted polymer and thus the grafting density; DSC was used to study the influence of the silica and blocks of the copolymer on their thermal behaviors. The glass transition temperature of the grafted copolymers was compared to these of free polymers or copolymers homologues.