Ag2S quantum dot-sensitized solar cells

We present a new photosensitizer – Ag₂S quantum dots (QDs) – for solar cells. The QDs were grown by the successive ionic layer adsorption and reaction deposition method. The assembled Ag₂S-QD solar cells yield a best power conversion efficiency of 1.70% and a short-circuit current of 1.54 mA/cm² under 10.8% sun. The solar cells have a maximal external quantum efficiency (EQE) of 50% at λ = 530 nm and an average EQE of ～ 42% over the spectral range of 400–1000 nm. The effective photovoltaic range covers the visible and near-infrared spectral regions and is ～ 2–4 times broader than that of the cadmium chalcogenide systems — CdS and CdSe. The results show that Ag₂S QDs can be used as a highly efficient and broadband sensitizer for solar cells.     

TiO2@CdS core–shell nanorods films: Fabrication and dramatically enhanced photoelectrochemical properties

In this paper, we prepared TiO₂@CdS core–shell nanorods films electrodes using a simple and low-cost chemical bath deposition method. The core–shell nanorods films electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–vis spectrometry techniques. After applying these TiO₂@CdS core–shell nanorods electrodes in photovoltaic cells, we found that the photocurrent was dramatically enhanced, comparing with those of bare TiO₂ nanorods and CdS films electrodes. Moreover, TiO₂@CdS core–shell nanorods film electrode showed better cell performance than CdS nanoparticles deposited TiO₂ nanoparticles (P25) film electrode. A photocurrent of 1.31 mA/cm², a fill factor of 0.43, an open circuit photovoltage of 0.44 V, and a conversion efficiency of 0.8% were obtained under an illumination of 32 mW/cm², when the CdS nanoparticles deposited on TiO₂ nanorods film for about 20 min. The maximum quantum efficiency of 5.0% was obtained at an incident wavelength of 500 nm. We believe that TiO₂@CdS core–shell heterostructured nanorods are excellent candidates for studying some fundamental aspects on charge separation and transfer in the fields of photovoltaic cells and photocatalysis.     

CdS/TiO2–SrTiO3 heterostructure nanotube arrays for improved solar energy conversion efficiency

TiO₂–SrTiO₃ heterostructure nanotube arrays have been utilized as a novel oxide substrate for CdS quantum dot sensitized solar cells (QDSCs). SrTiO₃ on TiO₂ surface passivates surface states of TiO₂ and builds cascade-structured band alignment, which significantly reduces charge recombination at electrode surface. CdS/TiO₂–SrTiO₃ electrode exhibits a superior photoelectrochemical performance than CdS/TiO₂ electrode with ～ 70% increase in external quantum efficiency. This study suggests that the suppression of charge recombination at electrode surface is critical to efficient solar energy conversion.     

Electrochemically synthesized CdS nanoparticle-modified TiO2 nanotube-array photoelectrodes: Preparation,characterization, and application to photoelectrochemical cells

A novel electrodeposited CdS nanoparticle-modified highly-ordered TiO₂ nanotube-array photoelectrode and its application to photoelectrochemical cells is reported. Results show formation of a thin, nanoparticulate CdS layer, comprised of sphere-like 10–20 nm diameter nanoparticles, on the anodic synthesized TiO₂ nanotube-array (inner diameter of 70 nm, wall thickness 25 nm and ca. 400 nm length) electrode. The resulting CdS–TiO₂ photoelectrode has an as-fabricated bandgap of 2.53, and 2.41 eV bandgap after sintering at 350 °C in N₂ ambient. Photoelectrochemical properties are described in detail.     

Recognition of DNA based on changes in the fluorescence intensity of CdSe/CD QDs–phenanthroline systems

The CdSe quantum dots (QDs) modified by mercapto-β-cyclodextrin (CD) were synthesized and characterized by transmission electron microscopy, powder X-ray diffraction, excitation and emission spectra, and fluorescence lifetime. When λ_ex = 370 nm, the fluorescence peak of CdSe/CD QDs is at 525 nm. Phenanthroline (Phen) is able to quench their fluorescence, which can be recovered by the addition of DNA. The quenching and restoration of fluorescence intensity were found to be linearly proportional to the amount of Phen and DNA, respectively. The variation of the fluorescence intensity of the CdSe/CD QDs–Phen system was studied, and it was demonstrated to result from a static mechanism due to the formation of a Phen inclusion complex with the CdSe QDs modified by mercapto-β-cyclodextrin. The fluorescence recovery was due to the binding of DNA with Phen in the inclusion complex, leading to the freeing of the CdSe/CD QDs. The binding constants and sizes of the binding sites of the Phen–DNA interaction were calculated to be 1.33 × 10⁷ mol^?1 L and 10.79 bp.     

Co-sensitization of vertically aligned TiO2 nanotubes with two different sizes of CdSe quantum dots for broad spectrum

In order to absorb a broad spectrum in the visible region, vertically aligned TiO₂ nanotubes (TONTs) were co-sensitized by two different sizes of CdSe quantum dots (Q dots). The power conversion efficiency of co-sensitized Q dots solar cells showed 1.20%. The co-sensitization of Q dots showed higher performance than the single size sensitization. The incident photon-to-current conversion efficiency of co-sensitized TONTs electrode showed two absorption peaks at 520 and 550 nm demonstrating the sensitization of Q dots with two different sizes. This efficiency enhanced charge harvesting efficiency over the entire visible spectrum, particularly the 500–600 nm wavelength domains.     

Spectral broadening in quantum dots-sensitized photoelectrochemical solar cells based on CdSe and Mg-doped CdSe nanocrystals

In order to absorb a broad spectrum in visible region, a co-sensitized TiO₂ electrode was prepared by CdSe and Mg-doped CdSe quantum dots (Q dots). The power conversion efficiency of the co-sensitized Q dots photoelectrochemical solar cells (PECs) showed 1.03% under air mass 1.5 condition (I = 100 mW/cm²), which is higher than that of individual Q dots-sensitized PECs. The incident-photon-to-current conversion efficiency of the co-sensitized PECs showed absorption peaks at 541 and 578 nm corresponding to the two Q dots and displayed a broad spectral response over the entire visible spectrum in the 500–600 nm wavelength domains.     

Highly efficient CdSe quantum-dot-sensitized TiO2 photoelectrodes for solar cell applications

With 4.2 nm quantum-dots (QDs) as seeds on TiO₂ film, a highly efficient TiO₂ photoelectrode was prepared by a seed-growing process using chemical bath deposition technique, followed by a covering process with ZnS layer, and a post-sintering process at 400 °C. The assembled solar cells presented IPCE peak values of 73% and power conversion efficiency of 3.21% under AM 1.5 G irradiation.     

Bubble-like CdSe nanoclusters sensitized TiO2 nanotube arrays for improvement in solar cell

Solar cells were fabricated using novel bubble-like CdSe nanoclusters sensitized highly ordered titanium oxide nanotube (TiO₂ NT) array, prepared by anodization technique. The CdSe sensitization of TiO₂ NT arrays was carried out by a chemical bath deposition method with freshly prepared sodium selenosufite, ammonium hydroxide and cadmium acetate dehydrate at different deposition times: 20, 40 and 60 min. The adsorption of CdSe nanoclusters on the upper and inner surface of the TiO₂ NT arrays has been confirmed by field emission scanning electron and transmission electron microscopes. The results show the variation in cell a performance with different deposition times (20, 40, and 60 min) of CdSe on TiO₂ NT arrays. The solar cell with CdSe, deposited for 60 min, shows reasonably high photovoltaic property compared to the reported results of similar studies. This solar cell shows the maximum photoelectric conversion efficiency of 1.56% (photocurrent of 7.19 mA/cm²; photovoltage of 0.438 V; and fill factor of 49.5%) and average incident photon to current efficiency of 50.2%. The photocurrent, incident photon-current efficiency and electron lifetime have been improved due to the increase of covered area and size of bubble-like CdSe nanoclusters on TiO₂ NT arrays with the increase of deposition time.     

CdSe/TiO2 nanocrystalline solar cells

CdSe sensitized TiO₂ nanocrystalline solar cells were made with the participation of silicotungstic acid (STA) during the deposition of CdSe, the resulting Voc and Isc were 0.23 V cm^-2 and 10 mA cm^-2, respectively. The doping, time and microporous membrane effects were also discussed.     

Chemical bath deposition of CdS quantum dots on vertically aligned ZnO nanorods for quantum dots-sensitized solar cells

Formation of CdS quantum dots (Q dots) on the vertically aligned ZnO nanorods electrode was carried out by chemical bath deposition. The diameter and thickness of ZnO nanorods are ～100–150 nm and ～1.6 μm, respectively, and CdS Q dots on ZnO nanorods have a diameter of smaller than 15 nm. In application of the Q dots-sensitized solar cells, composite film exhibited a power conversion efficiency of 0.54% under air mass 1.5 condition (80 mW/cm²), and incident-photon-to-current conversion efficiency showed 18.6%.     

AgSbS2 semiconductor-sensitized solar cells

We present a ternary semiconductor nanoparticle sensitizer – AgSbS₂ – for solar cells. AgSbS₂ nanoparticles were grown using a two-stage successive ionic layer adsorption and reaction process. First, Ag₂S nanoparticles were grown on the surface of a nanoporous TiO₂ electrode. Secondly, a Sb–S film was coated on top of the Ag₂S. The double-layered structure was transformed into AgSbS₂ nanoparticles ~ 40 nm in diameter, after post-deposition heating at 350 °C. The AgSbS₂-sensitized TiO₂ electrodes were fabricated into liquid-junction solar cells. The best cell yielded a power conversion efficiency of 0.34% at 1 sun and 0.42% at 0.1 sun. The external quantum efficiency (EQE) spectrum covered the range of 380–680 nm with a maximal EQE of 10.5% at λ = 470 nm. The method can be applied to grow other systems of ternary semiconductor nanoparticles for solar absorbers.     

Highly efficient quasi-solid-state quantum-dot-sensitized solar cell based on hydrogel electrolytes

Chemically crosslinked polyacrylamide-based hydrogel has been first used as the polymer matrix to prepare quasi-solid-state polysulfide electrolyte for CdS/CdSe co-sensitized solar cells (QDSCs). The room temperature ionic conductivity of the gel electrolyte reaches 0.093 S·cm^?1. QDSCs based on this quasi-solid-state electrolyte can present up to 4.0% of light-to-electricity conversion efficiency. Meanwhile, the interfacial recombination at TiO₂/electrolyte interface of the cell is also investigated by Electrochemical Impedance Spectroscopy (EIS).     

Dye-sensitized solar cells using anodic TiO2 mesosponge: Improved efficiency by TiCl4 treatment

In the present work, we produce 15 μm thick titania mesosponge layers (TMSL) by a Ti anodization/etching process and use the layers in dye-sensitized solar cells (DSCs). We show that the solar cell efficiency can considerably be improved by a TiCl₄ hydrolysis treatment (increase of approx. 40% to an overall value of 4.9% under AM 1.5 illumination). This beneficial effect is due to the decoration of the ～10 nm wide channels present in TMSL with TiO₂ nanoparticles of approx. 3 nm diameter, which allow for a significantly higher specific dye loading of the TMS structure.     

Quantum dots co-sensitized solar cells: a new assembly process of CdS/CdSe linked to mesoscopic TiO2-nano-SiO2 hybrid film

A green and simple method was found to prepare CdS/CdSe co-sensitized photoelectrodes for the quantum dots sensitized solar cells application. All the assembly processes of CdS and CdSe quantum dots (QDs) were carried out in aqueous solution. CdS and CdSe QDs were sequentially assembled onto TiO₂-nano-SiO₂ hybrid film by two steps. Firstly, CdS QDs were deposited in situ over TiO₂-nano-SiO₂ hybrid film by the successive ionic layer adsorption and reaction (SILAR) process in water. Secondly, using 3-mercaptopropionic acid (3-MPA) as a linker molecule, the pre-prepared colloidal CdSe QDs (~3.0 nm) dissolved in water was linked onto the TiO₂-nano-SiO₂ hybrid film by the self-assembled monolayer technique with the mode of dropwise. The mode is simple and advantageous to saving materials and time. The results show that the photovoltaic performance of the cells is enhanced with the increase of SILAR cycles for TiO₂-nano-SiO₂/CdS photoelectrode. The power conversion efficiency of 2.15 % was achieved using the co-sensitization photoelectrode prepared by using 6 SILAR cycles of CdS plus CdSe (TiO₂-nano-SiO₂/CdS(6)/CdSe) under the illumination of one sun (AM1.5, 100 mW/cm²).     

Photoelectrochemical determination of inorganic mercury ions based on energy transfer between CdS quantum dots and Au nanoparticles

A novel photoelectrochemical (PEC) sensor for mercury ions (Hg^2 +) was fabricated based on the energy transfer (ET) between CdS quantum dots (QDs) and Au nanoparticles (NPs) with the formation of T–Hg^2 +–T pairs. In the presence of Hg^2 + ions, a T-rich single-strand (ss) DNA labeled with Au NPs could hybridize with another T-rich ssDNA anchored on the CdS QDs modified electrode, through T–Hg^2 +–T interactions, rendering the Au NPs in close proximity with the CdS QDs and hence the photocurrent decrease due to the ET between the CdS QDs and the Au NPs. Under the optimal condition, the photocurrent decrease was proportional to the Hg^2 + concentration, ranging from 3.0 × 10^− 9 to 1.0 × 10^− 7 M, with the detection limit of 6.0 × 10^− 10 M.     

Influence of particle size on the photoactivity of Ti/TiO2 thin film electrodes,and enhanced photoelectrocatalytic degradation of indigo carmine dye

Photoanodes based on Ti/TiO₂ thin films were prepared by the sol–gel method, using either tetraisopropoxide (Ti(OPri)₄) or modified tetraisopropoxide, producing electrodes with different sized nanoparticle coatings, termed nanoporous (20 nm) or nanoparticulated (10 nm) electrodes. The anatase form dominated the composition of the nanoparticulated electrode, which presented a higher surface area, a flat band potential shift of ?160 mV and a 50% improvement in photoactivity, compared to the nanoporous electrode. 100% color removal, and 75% mineralization, of indigo carmine dye were achieved after 15 min of photoelectrocatalytic treatment using a nanoparticulated Ti/TiO₂ electrode operated at a current density of 0.4 mA cm^?2. Our findings indicate that the use of nanoparticulated electrodes, under UV irradiation and with controlled current density, is an efficient alternative for the removal of food dye contaminants during wastewater treatment.     

Tunable electrochemiluminescence of CdSe@ZnSe quantum dots by adjusting ZnSe shell thickness

CdSe quantum dots as cores capped with ZnSe shell (CdSe@ZnSe QDs) via a facile and eco-friendly strategy have been synthesized in aqueous solution for the first time. The electrochemiluminescence (ECL) of CdSe@ZnSe QDs was greatly enhanced compared to that of CdSe QDs. In particular, the ECL properties of the resulting CdSe@ZnSe QDs were found to be controllable by adjusting the thickness of ZnSe shells. Benefiting from the enhanced ECL intensity, the sensor based on CdSe@ZnSe QDs could accurately quantify dopamine from 10.0 nM to 3.0 μM with a detection limit of 3.6 nM.     

Energy Relay from an Unconventional Yellow Dye to CdS/CdSe Quantum Dots for Enhanced Solar Cell Performance

A new design for a quasi‐solid‐state Forster resonance energy transfer (FRET) enabled solar cell with unattached Lucifer yellow (LY) dye molecules as donors and CdS/CdSe quantum dots (QDs) tethered to titania (TiO₂) as acceptors is presented. The Forster radius is experimentally determined to be 5.29 nm. Sequential energy transfer from the LY dye to the QDs and electron transfer from the QDs to TiO₂ is followed by fluorescence quenching and electron lifetime studies. Cells with a donor–acceptor architecture (TiO₂/CdS/CdSe/ZnS‐LY/S^2?‐multi‐walled carbon nanotubes) show a maximum incident photon‐to‐current conversion efficiency of 53 % at 530 nm. This is the highest efficiency among Ru‐dye free FRET‐enabled quantum dot solar cells (QDSCs), and is much higher than the donor or acceptor‐only cells. The FRET‐enhanced solar cell performance over the majority of the visible spectrum paves the way to harnessing the untapped potential of the LY dye as an energy relay fluorophore for the entire gamut of dye sensitized, organic, or hybrid solar cells.     

Highly efficient dye-sensitized SnO2 solar cells having sufficient electron diffusion length

Dye-sensitized solar cells (DSCs) were fabricated from mesoporous SnO₂ electrodes, which were prepared from nano-sized SnO₂ particles. Current–voltage characteristics of the DSCs were compared with DSCs prepared from conventional TiO₂ electrodes, which have similar amount of adsorbed dye with the SnO₂. As a result, short-circuit current of the SnO₂DSC were comparable with that of the TiO₂DSCs, and more than 15 mA/cm² was obtained with the SnO₂ at the thickness of 10 μm under one sun conditions. Electron diffusion coefficients and lifetimes in the SnO₂ and TiO₂ electrodes were measured, showing slower diffusion and longer lifetime in the SnO₂DSC than in the TiO₂. The results imply that the electron transport and transfer dynamics in such electrodes is dominated by the influence of intra-band charge traps, and the control of the trap conditions would be the key strategy to employ various metal oxides for such solar cells.