Dye sensitized solar cells based on zinc oxide bottle brush

In this work, we report on the synthesis of zinc oxide (ZnO) bottle brush; by a cost effective and low temperature aqueous chemical route on fluorine doped tin oxide (FTO) coated conducting glass substrates. This bottle brush-like morphology enables 43% improvement in solar energy conversion efficiency as compared to the aligned nanorods (NRs). This improvement has been attributed to the more dye loading and effective light scattering within the photoelectrode. The light scattering increases the interaction between photons and dye molecules, hence increases the absorption. Also, the vertical NRs provide the direct path for electron transport for collection. The optical spectra reveal that the bottle brush-like structure has higher absorption as compared with the NRs.     

Field emission from nonaligned zinc oxide nanowires

Zinc oxide (ZnO) nanowires with an average diameter of 15 nm were grown using a vapor phase transport process. Field emission was achieved from these nanowires in spite of their random orientation. The electric field for the extraction of a 10 μA/cm² current density was measured to range from 4.4 to 5.0 V/μm, and that for a 1 mA/cm² current density from 7.6 to 8.7 V/μm, depending on whether the sample was submitted to a heat treatment. The results exhibit the potential application of ZnO nanowires as field emitters in future flat panel displays.     

Single-crystalline ZnO nanowires on zinc substrate by a simple hydrothermal synthesis method

A simple synthesis route to long ZnO nanowires with high aspect ratio of up to ∼ 1000 on zinc substrate in the NaOH aqueous solution was reported, without the assistance of any catalyst, templates or high temperature. We studied the key influencing factors including the reaction time and the solution concentration. With the increase of reaction time from 12 h to 24 h, the average length of ZnO nanowires would increase correspondingly. Through this synthesis route, we can obtain a mass of products and the method is both convenient and reproducible. The as-grown ZnO nanowires are single crystalline with a wurtzite structure.     

Aluminium doped zinc oxide sputtered from rotatable dual magnetrons for thin film silicon solar cells

This study addresses the electrical and optical properties as well as the surface structure after wet-chemical etching of mid-frequency magnetron sputtered aluminium doped zinc oxide (ZnO:Al) films on glass substrates from rotatable ceramic targets. Etching of an as-deposited ZnO:Al film in acid leads to rough surfaces with various feature sizes. The influence of working pressure and substrate temperature on the surface topography after etching was investigated. It was found that the growth model which Kluth et al. applied to films sputtered in radio frequency mode from planar ceramic target can be transferred to film growth from tube target. Furthermore, the influence of Ar gas flow and discharge power on the film properties was investigated. We achieved low resistivity of about 5.4 × 10^− 4 Ω·cm at high growth rates of 120 nm·m/min. Finally, surface textured ZnO:Al films were applied as substrates for microcrystalline silicon solar cells and high efficiencies of up to 8.49% were obtained.     

Humid environment stability of low pressure chemical vapor deposited boron doped zinc oxide used as transparent electrodes in thin film silicon solar cells

The stability in humid environment of low pressure chemical vapor deposited boron doped zinc oxide (LPCVD ZnO:B) used as transparent conductive oxide in thin film silicon solar cells is investigated. Damp heat treatment (exposure to humid and hot atmosphere) induces a degradation of the electrical properties of unprotected LPCVD ZnO:B layers. By combining analyses of the electrical and optical properties of the films, we are able to attribute this behavior to an increase of electron grain boundary scattering. This is in contrast to the intragrain scattering mechanisms, which are not affected by damp heat exposure. The ZnO stability is enhanced for heavily doped films due to easier tunneling through potential barrier at grain boundaries.     

The charge-transfer property and the performance of dye-sensitized solar cells of nitrogen doped zinc oxide

In this study two methods, namely the solution and annealing methods, were used to prepare nitrogen-doped ZnO. The X-ray photoelectron spectroscopy (XPS) was performed to identify the composition and chemical states of N-doped ZnO. The N doping by the solution method was found to effectively decrease the acceptor effects. Surface photovoltage measurements (SPS) revealed a redshift of the threshold wavelength for the N-doped ZnO. And the recombination of photoinduced electron–hole pairs in this semiconductor material was obviously suppressed. The N-doped ZnO (solution method) exhibits the best performances among all the materials, even superior to N-doped ZnO (annealing method). Its J_sc and η values (9.35 mA/cm² and 2.64%) have enhanced by several times compared with un-doped ZnO (J_sc, 2.85 mA/cm²; η, 0.67%). The overall conversion efficiency of ZnO-based dye-sensitized solar cells was successfully improved by the N doping.     

A novel approach for the synthesis of nanocrystalline zinc oxide powders by room temperature co-precipitation method

A single step co-precipitation route has been employed for the first time in the preparation of ZnO nanoparticles using ammonium hydroxide and zinc nitrate tetrahydrate. The X-ray diffraction analysis revealed that the synthesized powder has the hexagonal (wurtzite) structure. The as-prepared ZnO powder was well crystalline, without any calcination. This is a promising result compared to those mentioned in the literature, in which crystallization of ZnO nanoparticles was detected at > 300 °C. The average crystallite size of the as-prepared ZnO nanopowder is 20-40 nm. The nanocrystalline ZnO could be sintered to ~ 95% of the theoretical density at 1300 °C in 4 h.     

Novel and simple synthesis of ZnO nanospheres through decomposing zinc borate nanoplatelets

Spherical zinc oxide (ZnO) nanoparticles had been successfully synthesized through decomposing zinc borate nanoplatelets at high temperature. The resulted ZnO nanospheres were characterized by X-ray diffraction (XRD), which indicated that ZnO had the hexagonal structure. Field-emission-scanning electron micrographs (SEM) revealed that ZnO nanoparticles had perfect spherical shape with narrow size distribution (average diameters 50 nm). These nanoparticles showed a broad emission band centered at 438 nm using an excitation wave of 325 nm at room temperature. Moreover, the sample was characterized by N₂ adsorption-desorption and the pore size distribution showed a sharp peak at 3.1 nm.     

Improving low pressure chemical vapor deposited zinc oxide contacts for thin film silicon solar cells by using rough glass substrates

Compared to zinc oxide grown (ZnO) on flat glass, rough etched glass substrates decrease the sheet resistance (R_sq) of zinc oxide layers grown on it. We explain this R_sq reduction from a higher thickness and an improved electron mobility for ZnO layers deposited on rough etched glass substrates. When using this etched glass substrate, we also obtain a large variety of surface texture by changing the thickness of the ZnO layer grown on it. This new combination of etched glass and ZnO layer shows improved light trapping potential compared to ZnO films grown on flat glass. With this new approach, Micromorph thin film silicon tandem solar cells with high total current densities (sum of the top and bottom cell current density) of up to 26.8 mA cm^− 2 were fabricated.     

Fabrication of P3HT/PCBM solar cloth by electrospinning technique

Electrospinning of a conjugated polymer is not possible due to the absence of chain entanglement (it exists as a rigid rod conformation in a solution), which is a prerequisite for electrospinning. In the present study, fabrication of core-shell nanofibers has been done by co-electrospinning of two components such as poly(3-hexyl thiophene) (P3HT) (a conducting polymer) or P3HT/PCBM as the core and poly(vinyl pyrrolidone) (PVP) as the shell. The TEM observation and FTIR analysis confirmed the encapsulation of the P3HT within the PVP polymer. Continuous P3HT or P3HT/PCBM nanofibers have been obtained by subsequent washing of the shell polymer template in a post-treatment step. These nanofibers were tested for solar cloth applications.     

Chemically deposited nickel oxide as counter electrode for dye sensitized solar cell

Nickel oxide (NiO) thin films have been synthesized by simple and inexpensive chemical bath deposition at low temperature. The synthesized thin films were annealed at 623 K and used for further characterization. Structural and morphological properties of the NiO thin film were characterized using X-ray diffraction and scanning electron microscope (SEM), respectively. The structural study shows the simple cubic formation of NiO thin films with average crystallite size of 9 nm. Honeycomb like surface morphology with porous structure was observed from the SEM study. NiO thin film electrode has been used as a counter electrode in dye sensitized solar cell. Finally, photovoltaic parameters such as short circuit current density (J_sc), open circuit voltage (V_oc), Fill Factor (FF) and efficiency (η) have been studied.     

Controlled synthesis and characterization of 10 nm thick Al2O3 nanowires

α-Al₂O₃ nanowires, with diameter around 10 nm, were synthesized in bulk quantity by heating the mixture of pure aluminum and graphite powders at 900 °C. Scarcity of oxygen is regarded as the reason for the growth of the small diameter α-Al₂O₃ nanowires at relatively low temperature. The product was characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The Oxygen vacancies in the nanowires lead to the strong photoluminescence in the wavelength range of 400-700 nm with its peak at 527 nm.     

Preparation of TiO2 paste using poly(vinylpyrrolidone) for dye sensitized solar cells

The surface morphology of titanium oxide (TiO₂) films as a photoanode in dye sensitized solar cells plays a vital role in converting light to electricity. Therefore, TiO₂ films were prepared using TiO₂ paste with different compositions of poly(vinylpyrrolidone) (PVP) as a binder to optimize their physico-chemical properties. The paste was prepared with commercial TiO₂ powder mixed with acetylacetone, PVP, 4-octylphenol polyethoxylate, acetic acid and ethanol. The chemical composition remains the same for all pastes except PVP. The quantity of the PVP was optimized in such a way that it provides a thick film with a good network connection. The impact of the quantity of PVP in the TiO₂ paste was analyzed. The prepared TiO₂ film structure was characterized by X-ray diffraction. The surface morphology was analyzed by scanning electron microscopy. The electrochemical performance of the prepared TiO₂ as a photoanode was also investigated. Among the four different photoanodes, the cells fabricated with a TiO₂ film prepared with 0.4 g of PVP exhibited the highest power conversion efficiency of 6.77%, short-circuit photocurrent density and open circuit voltage of 12.38 mA/cm² and 0.77 V, respectively.     

The structural and electrical properties of Zn-Sn-O buffer layers and their effect on CdTe solar cell performance

Thin films of zinc-tin-oxide (ZTO) have been deposited on SnO₂:F coated glass substrates by co-sputtering of SnO₂ and ZnO. The deposition conditions for ZTO were controlled in order to vary film stoichiometry. The electro-optical and structural properties of ZTO have been studied as a function of their stoichiometric ratio and post-deposition annealing conditions. The same films were subsequently utilized as part of a bi-layer transparent front contact for the fabrication of CdTe solar cells: glass/SnO₂:F/ZTO. The performance of these devices suggested that the ZTO deposition and cell processing conditions can be optimized for enhanced device performance in particular for devices with thin CdS. Specifically, high blue spectral response (> 70% at 450 nm), accompanied by high open-circuit voltages (830 mV), and fill factors (70⁺%) have been demonstrated. Best solar cell performance was obtained for multi-phase ZTO films deposited at substrate temperatures of 400°C and a Zn/Sn ratio of 2.0, and which contained the binary phase of ZnO₂.     

Natively textured surface aluminum-doped zinc oxide transparent conductive layers for thin film solar cells via pulsed direct-current reactive magnetron sputtering

Natively textured surface aluminum-doped zinc oxide (ZnO:Al) layers for thin film solar cells were directly deposited without any surface treatments via pulsed direct-current reactive magnetron sputtering on glass substrates. Such an in-situ texturing method for sputtered ZnO:Al thin films has the advantages of efficiently reducing production costs and dramatically saving time in photovoltaic industrial processing. High purity metallic Zn-Al (purity: 99.999%, Al 2.0 wt.%) target and oxygen (purity: 99.999%) were used as source materials. During the reactive sputtering process, the oxygen gas flow rate was controlled using plasma emission monitoring. The performance of the textured surface ZnO:Al transparent conductive oxides (TCOs) thin films can be modified by changing the number of deposition rounds (i.e. thin-film thicknesses). The initially milky ZnO:Al TCO thin films deposited at a substrate temperature of ~ 553 K exhibit rough crater-like surface morphology with high transparencies (T ~ 80-85% in visible range) and excellent electrical properties (ρ ~ 3.4 × 10^− 4 Ω cm). Finally, the textured-surface ZnO:Al TCO thin films were preliminarily applied in pin-type silicon thin film solar cells.     

Study on the bulk junction type organic solar cells with double zinc oxide layer

The optical and photovoltaic properties of a photovoltaic cell with a structure of indium–tin oxide (ITO)/double ZnO/poly(3-hexylthiophene) (PAT6):PCBM/Ag have been investigated. The double layer ZnO was a composite of a sputtered ZnO layer and oriented zinc oxide nanopillars layer which was fabricated by a new method at low temperature (343 K). It is concluded that the double layer ZnO plays an important role in collecting photogenerated electrons and acts as a conducting path to the electrode. Insertion of the double layer ZnO in the photovoltaic cells produced enhanced performance with the power conversion efficiency of 1.42% under AM1.5 illumination.     

Novel Ga-doped ZnO nanocrystal ink: Synthesis and characterization

Ga-doped ZnO (GZO) nanocrystals were synthesized via the hot-injection method for the first time. The characterizations of its structure, composition, morphology, and absorption properties were conducted by using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and UV-vis absorption spectroscopy. The results indicated that GZO nanocrystals were single phase polycrystalline within a range of 5―10 nm. Optical measurements illustrated that GZO nanocrystals have a tunable band gap from 3.35 to 3.81 eV, depending on the Ga doping level. GZO nanocrystals were dispersed in nonpolar solvents to form a nanocrystal ink which could remain stable after a month of storage. The GZO thin film was fabricated by spin coating the GZO nanocrystal ink and annealing in air. The electrical resistivity of the film was measured to be 7.5 × 10⁻² Ω cm. This method, which eliminated the requirement of high vacuum and high temperature, was a promising alternative for transparent conducting oxide (TCO) fabrication.     

Covalent functionalization of zinc oxide nanowires for high sensitivity p-nitrophenol detection in biological systems

High-quality zinc oxide (ZnO) nanowires were synthesized using the atmospheric chemical vapor deposition technique and were appropriately characterized. Subsequently, the nanowire surface was covalently grafted with 1-pyrenebutyric acid (PBA) fluorophore, and surface-sensitive X-ray photoelectron spectroscopy and Fourier transform infrared-attenuated total reflectance spectroscopy were utilized to confirm the functionalization of 1-pyrenebutyric acid on the nanowire surface. Additionally, photoluminescence (PL) measurements were used to evaluate the optical behavior of pristine nanowires. Through fluorescence quenching of 1-pyrenebutyric acid by p-nitrophenol, a detection limit of 28 ppb was estimated. Based on these findings, ZnO nanowires functionalized with 1-pyrenebutyric acid are envisaged as extremely sensitive platforms for the ultra-trace detection of p-nitrophenol in biological systems.     

Preparation of SnS films with zinc blende structure by successive ionic layer adsorption and reaction method

Polycrystalline SnS thin films have been prepared by a modified SILAR (successive ionic layer adsorption and reaction) method, in which certain quantity of NH₄Cl was added to the cation precursor solution. The films have a novel zinc blende structure. The obtained SnS films are slightly rich in Sn component. There are small amounts of O impurity existing in the films, but no other impurity such as N or Cl is found in the films. The dark conductivity of the films is about 10^-6Ω^-1cm^-1. The polycrystalline films have a direct (forbidden) bandgap of 1.71 eV. The optical adsorption coefficient is above 10⁴ cm^-1 when the photon energy is larger than 1.4 eV.     

Synthesis of zinc and zinc oxide nanoparticles from zinc electrode using plasma in liquid

Nanoparticles are synthesized efficiently from zinc electrode by microwave plasma in liquid. The nanoparticles synthesized from alcohol resulted in pure zinc particles in the shape of spheres or hexagonal cylinders with a production rate of 3.3 g/h, and energy consumption of 267 J/mg for 1 mg. Whereas the nanoparticles synthesized in pure water are composed of Zn and ZnO. The Zn reacts with water through heat or the passage of time to become ZnO, releasing hydrogen gas. An upper disk placed 1 mm away from the electrode along with the bubbles generated simultaneously with the plasma ignition plays a key role in the synthesis of nanoparticles.