Wire-supported CdSe nanowire array photoelectrochemical solar cells

Previous fiber-shaped solar cells are based on polymeric materials or dye-sensitized wide band-gap oxides. Here, we show that efficient fiber solar cells can be made from semiconducting nanostructures (e.g. CdSe) with smaller band-gap as the light absorption material. We directly grow a vertical array of CdSe nanowires uniformly around a core metal wire and make the device by covering the top of nanowires with a carbon nanotube (CNT) film as the porous transparent electrode. The CdSe-CNT fiber solar cells show power conversion efficiencies of 1-2% under AM 1.5 illumination after the nanowires are infiltrated with redox electrolyte. We do not use a secondary metal wire (e.g. Pt) as in conventional fiber-shaped devices, instead, the end part of the CNT film is condensed into a conductive yarn to serve as the secondary electrode. In addition, our CdSe nanowire-based photoelectrochemical fiber solar cells maintain good flexibility and stable performance upon rotation and bending to large angles.     

Toward highly efficient CdS/CdSe quantum dots-sensitized solar cells incorporating ordered photoanodes on transparent conductive substrates

A series of ordered photoanodic architectures (including ordered TiO(2) nanotube arrays (TNT), ZnO nanorods, ZnO/TiO(2) core/shell nanostructures) for CdS/CdSe sensitized solar cells (QDSCs), were fabricated directly on transparent conductive oxide glasses by a facile sol-gel assisted template process. The morphologies, optical and electrical properties of TNTs and CdS/CdSe co-sensitized TNTs have been demonstrated. The effect of CdSe deposition time on the cell performance was clarified, and the growth mechanism of the CdSe quantum dots on the surface of the TNTs has been proposed as well. Furthermore, the evolution of open-circuit photovoltage (V(oc)) towards CdSe deposition time has been investigated by electrochemical impedance spectroscopy (EIS). A promising light-to-electricity conversion efficiency of up to 4.61% has been achieved with 3 μm long TNT arrays, which is the best record for sandwich-type ordered TNT-based QDSCs.     

Preparation of free-standing nanowire arrays on conductive substrates

By combining supercritical drying technique with AAO template-assisted electrodeposition, noncollapsed, vertically aligned, and free-standing nanowire arrays on a conductive Au film have been fabricated. We also demonstrate that these free-standing nanowire arrays can be feasibly used for fabricating nanowire-based electrically driven devices.     

High-performance silicon nanowire array photoelectrochemical solar cells through surface passivation and modification

Nanowire solar cells: Pt nanoparticle (PtNP) decorated C/Si core/shell nanowire photoelectrochemical solar cells show high conversion efficiency of 10.86 % and excellent stability in aggressive electrolytes under 1-sun AM 1.5 G illumination. Superior device performance is achieved by improved surface passivation of the nanowires by carbon coating and enhanced interfacial charge transfer by PtNPs.     

Self-assembled hybrid polymer-TiO2 nanotube array heterojunction solar cells

Films comprised of 4 microm long titanium dioxide nanotube arrays were fabricated by anodizing Ti foils in an ethylene glycol based electrolyte. A carboxylated polythiophene derivative was self-assembled onto the TiO2 nanotube arrays by immersing them in a solution of the polymer. The binding sites of the carboxylate moiety along the polymer chain provide multiple anchoring sites to the substrate, making for a stable rugged film. Backside illuminated liquid junction solar cells based on TiO2 nanotube films sensitized by the self-assembled polymeric layer showed a short-circuit current density of 5.5 mA cm-2, a 0.7 V open circuit potential, and a 0.55 fill factor yielding power conversion efficiencies of 2.1% under AM 1.5 sun. A backside illuminated single heterojunction solid state solar cell using the same self-assembled polymer was demonstrated and yielded a photocurrent density as high as 2.0 mA cm-2. When a double heterojunction was formed by infiltrating a blend of poly(3-hexylthiophene) (P3HT) and C60-methanofullerene into the self-assembled polymer coated nanotube arrays, a photocurrent as high as 6.5 mA cm-2 was obtained under AM 1.5 sun with a corresponding efficiency of 1%. The photocurrent action spectra showed a maximum incident photon-to-electron conversion efficiency (IPCE) of 53% for the liquid junction cells and 25% for the single heterojunction solid state solar cells.     

Highly efficient photoelectrochemical hydrogen generation using a ZnO nanowire array and a CdSe/CdS co-sensitizer

Highly efficient photoelectrochemical (PEC) hydrogen generation was achieved by fabricating CdSe deposited ZnO/CdS core/shell nanowire (NW) array photoanodes by a facile three-step solution-based method. Well-defined electrical pathways in 1-dimensional (1D) NW structures allowed efficient charge carrier collection, and CdSe/CdS co-sensitization enabled utilization of the visible region in the solar spectrum. PEC devices using CdSe/CdS/ZnO NW arrays showed improved absorption spectra, and they demonstrated a remarkable enhancement in PEC performance. Our proposed structure is a promising candidate photoanode for solar energy-to-hydrogen conversion devices.     

Hybrid heterojunction solar cell based on organic-inorganic silicon nanowire array architecture

Silicon nanowire arrays (SiNWs) on a planar silicon wafer can be fabricated by a simple metal-assisted wet chemical etching method. They can offer an excellent light harvesting capability through light scattering and trapping. In this work, we demonstrated that the organic-inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%. The high efficiency was ascribed to two aspects: one was the improvement of the light absorption by SiNWs structure on the planar components; the other was the enhancement of charge extraction efficiency, resulting from the novel top contact by forming a thin organic layer shell around the individual silicon nanowire. On the contrary, the sole planar junction solar cell only exhibited a PCE of 6.01%, due to the lower light trapping capability and the less hole extraction efficiency. It indicated that both the SiNWs structure and the thin organic layer top contact were critical to achieve a high performance organic/silicon solar cell.     

Cost-effective dye-sensitized solar cells consisting of two metal foils instead of transparent conductive oxide glass

A cost-effective structure for dye-sensitized solar cells (DSSCs) without using transparent conductive oxide (TCO) is reported. Instead of high-cost F/SnO(2) glass (FTO-glass) or woven metal mesh, a Ti foil and a perforation-patterned stainless steel (StSt) foil are introduced as the substrates for a counter-electrode and a photo-electrode, respectively.     

Synthesis of nickel nanowires via electroless nanowire deposition on micropatterned substrates

Electroless nanowire deposition on micropatterned substrates (ENDOM) is a promising new technique by which to direct the synthesis and precise placement of metallic nanowires. ENDOM is generally applicable to the preparation of metallic, semiconducting, and even insulating nanowires on technologically relevant substrates, is inexpensive, and can achieve high growth rates. The deposited nanowires are ultralong (centimeters) and can be patterned in arbitrary shapes. We demonstrate ENDOM using the growth of nickel nanowires. By controlling the deposition time, the width of the nanowires can be varied from 200 to 1000 nm and the height can be varied from 7 to 20 nm.     

利用鲑鱼精DNA为模板构建CdS纳米线

以鲑鱼精DNA为模板合成了CdS纳米粒子，透射电子显微观察表明所生成的CdS是一种直径约为3nm的线形结构，紫外-可见吸收光谱，拉曼光谱和X-射线光电子能谱结果表明，CdS纳米粒子的生长点为DNA中的磷酸根，并且在这一体系中可能存在从CdS到DNA中碱基的电子转移。     

Photoassisted interfacial charge transfers at inhomogeneous semiconducting film-electrolyte junction in photoelectrochemical cells: Case of CdS and CdS(Al) sprayed films on to conductive glass

Photoassisted charge transfers at conductive glass based CdS and Al-doped CdS sprayed films only 0.5 μm thick in contact with an electrolyte are studied. Al is found to improve the photocurrent.     

Multilayer assembly of nanowire arrays for dye-sensitized solar cells

Vertically ordered nanostructures synthesized directly on transparent conducting oxide have shown great promise for overcoming the limitations of current dye-sensitized solar cells (DSCs) based on random networks of nanoparticles. However, the synthesis of such structures with a high internal surface area has been challenging. Here we demonstrate a convenient approach that involves alternate cycles of nanowire growth and self-assembled monolayer coating processes for synthesizing multilayer assemblies of ZnO nanowire arrays and using the assemblies for fabrication of DSCs. The assembled multilayer ZnO nanowire arrays possess an internal surface area that is more than 5 times larger than what one can possibly obtain with single-layer nanowire arrays. DSCs fabricated using such multilayer arrays yield a power conversion efficiency of 7%, which is comparable to that of TiO(2) nanoparticle-based DSCs. The ordered structure with a high internal surface area opens up opportunities for further improvement of DSCs.     

Current density enhancement for quantum dot-sensitized solar cells by modulation on the quantum dot loading amount of anatase nanowire array photoelectrodes

Journal of Solid State Electrochemistry - A second spin-coating process was employed for CuInS2 quantum dot (QD)-sensitized TiO2 nanowire-based solar cells, which is anticipated to increase the QD...     

Sea urchin TiO2-nanoparticle hybrid composite photoelectrodes for CdS/CdSe/ZnS quantum-dot-sensitized solar cells

The sea urchin TiO(2) (SU TiO(2)) particles composed of radially aligned rutile TiO(2) nanowires are successfully synthesized through the simple solvothermal process. SU TiO(2) was incorporated into the TiO(2) nanoparticle (NP) network to construct the SU-NP composite film, and applied to the CdS/CdSe/ZnS quantum-dot-sensitized solar cells (QDSSCs). A conversion efficiency of 4.2% was achieved with a short-circuit photocurrent density of 18.2 mA cm(-2) and an open-circuit voltage of 531 mV, which corresponds to ～20% improvement as compared with the values obtained from the reference cell made of the NP film. We attribute this extraordinary result to the light scattering effect and efficient charge collection.     

High efficiency hybrid solar cells using post-deposition ligand exchange by monothiols

High-performance hybrid solar cells (HSCs) based on P3HT?:?CdSe QD blends are achieved through post-deposition ligand exchange by n-butanethiol (n-BT) with a high power conversion efficiency of 3.09%. The mechanism by which n-BT modifies the surface structures of CdSe QDs and thus improves the HSCs performance is investigated.     

Ion-exchange synthesis and improved photovoltaic performance of CdS/Ag2S heterostructures for inorganic-organic hybrid solar cells

A facile ultrasound-assisted ion exchange route was developed for the synthesis of CdS/Ag₂S heterojunctions by ion exchange between the nanostructured CdS film and [Ag(NH₃)₂]⁺ under ultrasonication. The CdS/Ag₂S heterojunction film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis DRS spectroscopy, photoelectrochemical measurements, and the transient photovoltage (TPV) technique. CdSAg₂S heterojunctions exhibit a dense morphology, enhanced visible light absorption and stronger photocurrent response than the pure CdS films. Poly(3-hexylthiophene) (P3HT) was then spin coated into the CdS/Ag₂S framework. Hybrid solar cells constructed with FTO/CdS/Ag₂S/P3HT/Au display relatively higher power conversion efficiency than FTO/CdS/P3HT/Au.     

Synthesis of uniform CdS nanowires in high yield and its single nanowire electrical property

Large-scale high quality CdS nanowires with uniform diameter were synthesized by using a rapid and simple solvothermal route. Field emission scan electron microscopy (FESEM) and transmission electron microscopy (TEM) images show that the CdS nanowires have diameter of about 26 nm and length up to several micrometres. High resolution TEM (HRTEM) study indicates the single-crystalline nature of CdS nanowires with an oriented growth along the c-axis direction. The optical properties of the products were characterized by UV-vis absorption spectra, photoluminescence spectra and Raman spectra. The resistivity, electron concentration and electron mobility of single NW are calculated by fitting the symmetric I-V curves measured on single NW by the metal-semiconductor-metal model based on thermionic field emission theory.     

Dye-sensitized solar cells based on anatase TiO2 nanoparticle/nanowire composites

Dye-sensitized solar cells were fabricated based on the composites of anatase TiO2 nanoparticles and single crystalline anatase TiO2 nanowires. Nanoparticle/nanowire composites can possess the advantages of both building blocks, i.e., the high surface area of nanoparticle aggregates and the rapid electron transport rate and the light scattering effect of single-crystalline nanowires. Three different composites were prepared with 5 wt %, 20 wt %, and 77 wt % nanowires, respectively. The performances of composite solar cells were compared with pure nanoparticle cells at a series of film thickness. With low nanowire concentrations (5 wt % and 20 wt %), the composite films maintain similar specific surface area as the pure nanoparticle films, while the composite cells show higher short-circuit current density and open-circuit voltage. An enhancement of power efficiency from 6.7% for pure nanoparticle cells to 8.6% for the composite cell with 20 wt % nanowires has been achieved under 1 Sun AM1.5 illumination (100 mW/cm2). For the composite film with 77 wt % nanowires, the nanowires became the major phase. Their less compact packing resulted in significant decrease of the specific surface area, and thus the current density. However, with the increase of film thickness, the current density showed a continuous increase in the whole thickness range up to 17 microm, indicating the improved electron diffusion length due to the formed nanowire network. The nanowires also helped to preserve crack-free thick films. These results show that employing nanoparticle/nanowire composites represents a promising approach for further improving the efficiencies of sensitized solar cells.     

Synthesis and characterization of conductive polypyrrole grown on the sulfonated surface of polyethylene films

Chemical synthesis of polypyrrole (PPy) was carried out in the presence of FeCl₃ aqueous solution. The grown PPy is fixed on the sulfonated surface of polyethylene (SPE) films, where the sulfonic groups act as counteranions to balance the positive charge of PPy, giving the composite material of PPy–SPE. For reasons of comparison, two types of polyethylene (PE) have been used, low and high densities with different degrees of sulfonation, SD (g/m²), defined as the ratio of weight increase to the area of the two surfaces of the sample. A series of reaction times was used to evaluate the variation of the electrical conductivity, σ (S/cm), of polypyrrole. It was found that σ increases as reaction time increases. To characterize the samples, Fourier transform infrared (FTIR) spectroscopy and conductivity measurements were performed.     

Performance enhancement of CdS nanorod arrays/P3HT hybrid solar cells via N719 dye interface modification

Improved hybrid solar cells consisting of vertical aligned cadmium sulfide (CdS) nanorod arrays and interpenetrating polythiophene (P3HT) have been achieved via modification of CdS nanorod surface by using conjugated N719 dye. The complete infiltration of P3HT between CdS nanorods interspacing was verified by scanning electron microscopy. By employing absorption and photoluminescence spectra, and current-voltage characterization the interaction between N719 molecules and CdS nanorods/P3HT interface was explored, and the role of N719 dye on the improvement of device performance was discussed.