ZnO/TiO2 nanocable structured photoelectrodes for CdS/CdSe quantum dot co-sensitized solar cells

Radial ZnO nanorods decorating Co3O4 nanoparticles for highly selective and sensitive detection of the 3-hydroxy-2-butanone biomarker

Indirect monitoring of Listeria monocytogenes (LM) via a gas sensor that can detect the bacterial metabolite 3-hydroxy-2-butanone (3H-2B) is a newly emerged strategy. However, such sensors are required simultaneously endow with outstanding selectivity, high sensitivity, and ppb-level detection limit, which remains technologically challenging. Herein, we have developed highly selective and sensitive 3H-2B sensors that consist of zinc oxide nanorods decorated with cobaltosic oxide nanoparticles (ZnO NRs/Co₃O₄ NPs), which have been synthesized by combined optimized hydrothermal and annealing process. Specifically, the ZnO NRs/Co₃O₄ NPs exhibit ultrahigh sensitivity to 5 ppm 3H-2B (R_a/R_g = 550 at 260 °C). The sensor prototypes enable detection as low as 10 ppb 3H-2B, show excellent long-term stability, and present remarkable selectivity through interfering selectivity survey and principal component analysis (PCA). Such outstanding sensing performance is attributed to the modulated electron depletion layer by n-p heterojunctions and abundant gas diffusion pathways via the radial architecture, which was verified via electrochemical impedance spectroscopy test, Mott-Schottky measurement, and ultraviolet-visible absorption analysis. Our highly selective and sensitive ZnO NRs/Co₃O₄ NPs have the potential in the real-time detection of 3H-2B biomarker.

Quantum Dot Sensitized Solar Cell: Photoanodes, Counter Electrodes, and Electrolytes

In this study, we provide the reader with an overview of quantum dot application in solar cells to replace dye molecules, where the quantum dots play a key role in photon absorption and excited charge generation in the device. The brief shows the types of quantum dot sensitized solar cells and presents the obtained results of them for each type of cell, and provides the advantages and disadvantages. Lastly, methods are proposed to improve the efficiency performance in the next researching.

ZnO nanowires for solar cells: a comprehensive review

As an abundant and non-toxic wide band gap semiconductor with a high electron mobility, ZnO in the form of nanowires (NWs) has emerged as an important electron transporting material in a vast number of nanostructured solar cells. ZnO NWs are grown by low-cost chemical deposition techniques and their integration into solar cells presents, in principle, significant advantages including efficient optical absorption through light trapping phenomena and enhanced charge carrier separation and collection. However, they also raise some significant issues related to the control of the interface properties and to the technological integration. The present review is intended to report a detailed analysis of the state-of-the-art of all types of nanostructured solar cells integrating ZnO NWs, including extremely thin absorber solar cells, quantum dot solar cells, dye-sensitized solar cells, organic and hybrid solar cells, as well as halide perovskite-based solar cells.

Reducing the Schottky Barrier by SnS2 Underlayer Modification to Enhance Photoelectric Performance: The Case of Ag2S/FTO

The transfer and recombination of photoinduced charge carriers play the crucial roles in a photoelectric conversion system. In this work, the Ag₂S/fluorine-doped tinoxide (FTO) was used as the platform to understand the photoinduced charge carrier transfer and recombination at the light absorber and electrode interface. SnS₂ was evaporated onto the FTO surface to cooperate the Fermi level with Ag₂S, which reduced the Schottky barrier at the Ag₂S/FTO interface. Kelvin probe force microscopy measurements reveal that the Fermi level of FTO can be tuned from -4.93 to -4.75 eV by various SnS₂ with different evaporation amounts. Transient surface photovoltage tests confirm that the recombination of the photogenerated charge carrier can be drastically suppressed. The photoelectric conversion efficiency of the resulting solar cell devices has been significantly improved.

Hidden energy levels? Carrier transport ability of CdS/CdS1-xSex quantum dot solar cells impacted by Cd-Cd level formation

In quantum dot sensitized solar cells (QDSSC), a cascade energy level structure controlled by assembly of cadmium-chalcogenide quantum dots can remarkably improve the sunlight harvesting and charge carrier lifetime. Despite the advantages of using co-sensitizers, energy conversion efficiencies are still low. An increased understanding of the causes of the low photoconversion efficiency (PCE) will contribute to the development of a straightforward approach to improve solar cell performance by exploiting co-sensitization. Herein we discuss how an excess of cadmium causes structural disorder and defect levels impacting the PCE of QDSSC devices. Thus, outer CdS1-xSex/inner CdS QD-co-sensitized B,N,F-co-doped-TiO2 nanotubes (BNF-TNT) were prepared. Chalcogenides were deposited by the SILAR method on BNF-TNT, varying the load of CdS as the inner sensitizer, while for CdS1-xSex, five SILAR cycles were used (5-CdS1-xSex), controlling the nominal S/Se molar ratio of the ternary alloy. Cd defects named as Cd-Cd energy levels were observed during CdS sensitization. Although incorporation of outer CdS1-xSex provides a tunable band gap to achieve good band alignment for carrier separation, Cd-Cd energy levels in the sensitizers act as recombination centers, limiting the overall electron flow at the BNF-TNT/CdS/CdS1-xSex interface. A maximum PCE of 2.58% was reached under standard AM 1.5G solar illumination at 100 mW cm-2. Additional limitations of SILAR as a deposition strategy of QDs are also found to influence the PCE of QDSSC.

Design of SnO₂ Aggregate/Nanosheet Composite Structures Based on Function-Matching Strategy for Enhanced Dye-Sensitized Solar Cell Performance

Hierarchical SnO₂ nanocrystallites aggregates (NAs) were prepared with a simple room temperature–based aqueous solution method followed by simple freeze-drying treatment. The as-prepared SnO₂ NAs were subsequently combined with SnO₂ nanosheet–based structures from the viewpoint of a function-matching strategy, and under an optimized condition, a power conversion efficiency (PCE) of 5.59% was obtained for the resultant hybrid photoanode, a remarkable 60% enhancement compared to that of dye-sensitized solar cells (DSCs) fabricated with bare SnO₂ NAs architecture. The significantly enhanced efficiency can be attributed to the combination of the desirable electron transport property obtained by the intentionally introduced SnO₂ nanosheets (NSs) and the effectively retained inherent characteristics of SnO₂ NAs, i.e., large surface area and strong light-scattering effect. This work provides a promising approach for the rapid development of highly efficient SnO₂ photoanode film-based DSCs with the properties of simplicity of operation and control over the photoanode composition.

Heterostructured TiO2/NiTiO3 Nanorod Arrays for Inorganic Sensitized Solar Cells with Significantly Enhanced Photovoltaic Performance and Stability

Organic dyes used in the conventional dye-sensitized solar cells (DSSCs) suffer from poor light stability and high cost. In this work, we demonstrate a new inorganic sensitized solar cell based on ordered one-dimensional semiconductor nanorod arrays of TiO₂/NiTiO₃ (NTO) heterostructures prepared via a facile two-step hydrothermal approach. The semiconductor heterostructure arrays are highly desirable and promising for DSSCs because of their direct charge transport capability and slow charge recombination rate. The low-cost NTO inorganic semiconductor possesses an appropriate band gap that matches well with TiO₂, which behaves like a "dye" to enable efficient light harvesting and fast electron-hole separation. The solar cells constructed by the ordered TiO₂/NTO heterostructure photoanodes show a significantly improved power conversion efficiency, high fill factor, and more promising, outstanding life stability. The present work will open up an avenue to design heterostructured inorganics for high-performance solar cells.

Zinc-aluminum oxide solid solution nanosheets obtained by pyrolysis of layered double hydroxide as the photoanodes for dye-sensitized solar cells

Due to the superiority of metal-doped ZnO compared to TiO₂, the Zn-M (M = Al³⁺, Ga³⁺, Cr³⁺, Ti⁴⁺, Ce⁴⁺) mixed metal oxide solid solutions have been extensively studied for photocatalytic and photovoltaic applications. In this work, a systematic research has proceeded for the preparation of a zinc-aluminum oxide semiconductor as a photoanode for the dye-sensitized solar cells (DSSCs) by a simple pyrolysis route with the Zn-Al layered double hydroxide (LDH) as a precursor. The Zn-Al oxide solid solution has been applied for DSSCs as an electron acceptor, which is used to study the influence of different Al content and sintering temperature on the device efficiency. Finally, the Zn-Al oxide solid solution with calcination temperature 600 °C and Al 27 at.% content exhibits the best performance. The photoelectric efficiency improved 100 times when the Al³⁺ content decreased from 44 to 27 at.%. The Zn_xAl_yO solid solution show a reasonable efficiency as photoanode materials in DSSCs, with the best preliminary performance reported so far, and shows its potential application for the photovoltaic devices.

Charge recombination control for high efficiency CdS/CdSe quantum dot co-sensitized solar cells with multi-ZnS layers

ZnS as an inorganic passivation agent has been proven to be effective in suppressing charge recombination and enhancing power conversion efficiency (PCE) in quantum dot-sensitized solar cells (QDSCs).

Assembly of CdS nanoparticles on boron and fluoride co-doped TiO2 nanofilm for solar energy conversion applications

Boron and fluoride co-doped TiO₂ nanomaterial is successfully synthetized using a facile process, followed by chemical bath deposition in an organic solution to ensure high wettability and superior penetration ability of the B/F co-doped TiO₂ films.

High Efficiency CdS/CdSe Quantum Dot Sensitized Solar Cells with Two ZnSe Layers

CdS/CdSe quantum dot sensitized solar cells (QDSCs) have been intensively investigated; however, most of the reported power conversion efficiency (PCE) is still lower than 7% due to serious charge recombination and a low loading amount of QDs. Therefore, suppressing charge recombination and enhancing light absorption are required to improve the performance of QDSCs. The present study demonstrated successful design and fabrication of QDSCs with a high efficiency of 7.24% based on CdS/CdSe QDs with two ZnSe layers inserted at the interfaces between QDs and TiO₂ and electrolyte. The effects of two ZnSe layers on the performance of the QDSCs were systematically investigated. The results indicated that the inner ZnSe buffer layer located between QDs and TiO₂ serves as a seed layer to enhance the subsequent deposition of CdS/CdSe QDs, which leads to higher loading amount and covering ratio of QDs on the TiO₂ photoanode. The outer ZnSe layer located between QDs and electrolyte behaves as an effective passivation layer, which not only reduces the surface charge recombination, but also enhances the light harvesting.

CdS/CdSe Co-sensitized Solar Cells Based on Hierarchically Structured SnO2/TiO2 Hybrid Films

SnO2 nanosheet-structured films were prepared on a fluorine-doped tin oxide (FTO) substrate using ZnO nanosheet as template. The as-prepared SnO2 nanosheets contained plenty of nano-voids and were generally vertical to the substrate. TiO2 nanoparticles were homogeneously deposited into the intervals between the SnO2 nanosheets to prepare a hierarchically structured SnO2/TiO2 hybrid film. The hybrid films were co-sensitized with CdS and CdSe quantum dots. The sensitized solar cells assembled with the SnO2/TiO2 hybrid film showed much higher photoelectricity conversion efficiency than the cells assembled with pure TiO2 films. The lifetime of photoinduced electron was also investigated through electrochemical impedance spectroscopy, which showed that the SnO2/TiO2 hybrid film electrode is as long as the TiO2 film electrode.

Efficiency Enhancement of Quantum Dot Sensitized TiO2/ZnO Nanorod Arrays Solar Cells by Plasmonic Ag Nanoparticles

A high efficiency quantum dot sensitized solar cell (QDSC) based on Ag nanoparticles (NPs) decorated TiO₂/ZnO nanorod arrays (NAs) photoelectrode has been constructed. The incorporation of Ag NPs to TiO₂/ZnO NAs photoelectrode not only increases light harvesting efficiency and facilitates exciton dissociation but also decreases surface charge recombination and prolongs electron lifetime, which collectively contribute to improving the J_sc of the CdS/CdSe QDs cosensitized solar cells. The direct contact of Ag NPs with TiO₂ NPs is undergoing Fermi level alignment; thus, the apparent Fermi level is supposed to trigger an upward shift of more negative potential, which results in an increase the V_oc of the QDSCs. As a result, the power conversion efficiency of the QDSCs with Ag NPs decorated TiO₂/ZnO NAs photoelectrode reached 5.92%, which is about 22% enhancement of the efficiency for the solar cells without Ag NPs (4.80%).

A structure of CdS/CuxS quantum dots sensitized solar cells

This work introduces a type of CdS/Cu_xS quantum dots (QDs) as sensitizers in quantum dot sensitized solar cells by in-situ cationic exchange reaction method where CdS photoanode is directly immersed in CuCl₂ methanol solution to replace Cd²⁺ by Cu²⁺. The p-type Cu_xS layer on the surface of the CdS QDs can be considered as hole transport material, which not only enhances the light harvesting of photoanode but also boosts the charge separation after photo-excitation. Therefore, both the electron collection efficiency and power conversion efficiency of the solar cell are improved from 80% to 92% and from 1.21% to 2.78%, respectively.

CdS/CdSe co-sensitized hierarchical TiO2 nanofiber/ZnO nanosheet heterojunction photoanode for quantum dot-sensitized solar cells

Hierarchical ZnO nanosheets branched TiO₂ non-woven fabric film is used as efficient photoanode for QDSSCs.

Anatase TiO2 nanosheets with exposed highly reactive (001) facets as an efficient photoanode for quantum dot-sensitized solar cells

Two-dimensional (2D) anatase TiO₂ nanosheets (TiO₂-NSs) with exposed (001) crystal planes were obtained via a simple one-pot hydrothermal route, and a high efficient CdSe quantum dots solar cell was obtained based on the TiO₂ nanosheets photoanode.

Strain-tuned optoelectronic properties of hollow gallium sulphide microspheres

Sulfide semiconductors have attracted considerable attention. The main challenge is to prepare materials with a designable morphology, a controllable band structure and optoelectronic properties. Herein, we report a facile chemical transportation reaction for the synthesis of Ga2S3 microspheres with novel hollow morphologies and partially filled volumes. Even without any extrinsic dopant, photoluminescence (PL) emission wavelength could be facilely tuned from 635 to 665 nm, depending on its intrinsic inhomogeneous strain distribution. Geometric phase analysis (GPA) based on high-resolution transmission electron microscopy (HRTEM) imaging reveals that the strain distribution and the associated PL properties can be accurately controlled by changing the growth temperature gradient, which depends on the distance between the boats used for raw material evaporation and microsphere deposition. The stacking-fault density, lattice distortion degree and strain distribution at the shell interfacial region of the Ga2S3 microspheres could be readily adjusted. Ab initio first-principles calculations confirm that the lowest conductive band (LCB) is dominated by S-3s and Ga-4p states, which shift to the low-energy band as a result of the introduction of tensile strain, well in accordance with the observed PL evolution. Therefore, based on our strain driving strategy, novel guidelines toward the reasonable design of sulfide semiconductors with tunable photoluminescence properties are proposed.

Control of Nanostructures and Interfaces of Metal Oxide Semiconductors for Quantum-Dots-Sensitized Solar Cells

Nanostructured metal oxide semiconductors (MOS), such as TiO2 and ZnO, have been regarded as an attractive material for the quantum dots sensitized solar cells (QDSCs), owing to their large specific surface area for loading a large amount of quantum dots (QDs) and strong scattering effect for capturing a sufficient fraction of photons. However, the large surface area of such nanostructures also provides easy pathways for charge recombination, and surface defects and connections between adjacent nanoparticles may retard effective charge injection and charge transport, leading to a loss of power conversion efficiency. Introduction of the surface modification for MOS or QDs has been thought an effective approach to improve the performance of QDSC. In this paper, the recent advances in the control of nanostructures and interfaces in QDSCs and prospects for the further development with higher power conversion efficiency (PCE) have been discussed.

Remarkable enhancement of photovoltaic performance of ZnO/CdTe core–shell nanorod array solar cells through interface passivation with a TiO2 layer

The power conversion efficiency of the ZnO/CdTe core–shell nanorod array solar cell can be dramatically improved with a thin passivation TiO₂ layer on the interface.

Surface engineering of ZnO nanostructures for semiconductor-sensitized solar cells

Semiconductor-sensitized solar cells (SSCs) are emerging as promising devices for achieving efficient and low-cost solar-energy conversion. The recent progress in the development of ZnO-nanostructure-based SSCs is reviewed here, and the key issues for their efficiency improvement, such as enhancing light harvesting and increasing carrier generation, separation, and collection, are highlighted from aspects of surface-engineering techniques. The impact of other factors such as electrolyte and counter electrodes on the photovoltaic performance is also addressed. The current challenges and perspectives for the further advance of ZnO-based SSCs are discussed.

Hierarchically structured ZnO nanorods-nanosheets for improved quantum-dot-sensitized solar cells

ZnO nanorods (NRs) and nanosheets (NSs) were fabricated by adjusting the growth orientation of ZnO crystals in the reaction solution, respectively. The thin ZnO NSs were slowly assembled on the surface of NRs to form a hierarchically structured NR-NS photoelectrode for constructing CdS/CdSe quantum-dot-sensitized solar cells (QDSCs). This hierarchical structure had two advantages in improving the power conversion efficiency (PCE) of the solar cells: (a) it increased the surface area and modified the surface profile of the ZnO NRs to aid in harvesting more quantum dots, which leads to a high short-current density (Jsc); (b) it facilitated transportation of the electrons in this compact structure to reduce the charge recombination, which led to enhancement of the open-circuit voltage (Voc) and fill factor (FF). As a result, the QDSC assembled with the hierarchical NR-NS photoelectrode exhibited a high PCE of 3.28%, which is twice as much as that of the NR photoelectrode (1.37%).

TiO2@CdSe/CdS core–shell hollow nanospheres solar paint

TiO₂@CdSe/CdS hollow nanospheres solar paint were fabricated and directly applied in quantum dot-sensitized solar cell. The reliable conversion efficiency of 0.79 was achieved with a current density of 6.6 mA cm⁻².

Hybrid bulk heterojunction solar cells based on the cooperative interaction of liquid crystals within quantum dots and diblock copolymers

In this article, the conjugated rod-rod polythiophene diblock copolymers comprising a regioregular poly(3-hexylthiophene) (P3HT) segment and a side-chain liquid-crystalline polythiophene segment bearing cyanobiphenyl mesogenic pendants (PTcbp), polythiophene-b-poly{3-[10-(4'-cyanobiphenyloxy)decyl]thiophene} (P3HT-b-PTcbp), were rationally designed and synthesized. It was observed that the diblock copolymers could self-assemble into high crystalline and oriented nanofibrils upon 1,2-dichlorobenzene solvent vapor annealing, originating from the crystallization of two segments and the orientation of cyanobiphenyl side-chain mesogens. Hybrid bulk heterojunction (BHJ) solar cells were then fabricated using P3HT-b-PTcbp as electron donors and ZnO and CdS quantum dots (QDs) modified by 4'-hydroxy-[1,1'-biphenyl]-4-carbonitrile (cbp) liquid-crystalline ligands (cbp@ZnO and cbp@CdS) as electron acceptors. The interaction between the cbp ligands on the surface of ZnO and CdS QDs and cyanobiphenyl side-chain mesogens of diblock copolymers promoted the cooperative self-assembly and controllable well-dispersion of QDs in the polymer matrix and, as a consequence, yielded an intimately contacted polymer-QD nanocomposites. The power conversion efficiency (PCE) of the device based on P3HT-b-PTcbp/cbp@ZnO hybrids was improved by 2.6 times compared with that of P3HT/ZnO hybrids from 0.58 to 0.97. In addition, an overall PCE of a homologous device based on the P3HT-b-PTcbp/cbp@CdS hybrid active layer reached 2.3%. The research paved the way for the further development of high-efficiency hybrid BHJ solar cells by introducing block copolymer nanofibrils with favored crystalline domain orientations and liquid-crystalline organization properties.

Hierarchical macroporous Zn(2)SnO(4)-ZnO nanorod composite photoelectrodes for efficient CdS/CdSe quantum dot co-sensitized solar cells

A hierarchical macroporous Zn2SnO4-ZnO nanorod composite film is prepared through a drop-casting process of PS@Zn2SnO4 and subsequent hydrothermal growth of ZnO nanorod. CdS/CdSe co-sensitized solar cells based on the macroporous Zn2SnO4-ZnO nanorod composite photoelectrode exhibits an enhancement of 34.4% in power conversion efficiency (1.68%) compared to the pristine macroporous Zn2SnO4 photoelectrode (1.25%). Especially worth noting is that the growth of ZnO nanorods contributes greatly to the enlargement of surface area and improvement of light scattering ability of the composite film, which dominates the increase of Jsc values and eventual power conversion efficiency. QDSSCs based on the optimized 9 μm thick composite photoanode film exhibits a power conversion efficiency of 2.08%, which is the highest value for the reported QDs sensitized solar cells based on the Zn2SnO4 photoelectrode.

Improved performance of CuInS2 quantum dot-sensitized solar cells based on a multilayered architecture

This article describes a CuInS2 quantum dot (QD)-sensitized solar cell (QDSSC) with a multilayered architecture and a cascaded energy-gap structure fabricated using a successive ionic-layer adsorption and reaction process. We initially used different metal chalcogenides as interfacial buffer layers to improve unmatched band alignments between the TiO2 and CuInS2 QD sensitizers. In this design, the photovoltaic performance, in terms of the short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF), and power conversion efficiency (PCE), was significantly improved. Both JSC and VOC were improved in CuInS2-based QDSSCs in the presence of interfacial buffer layers because of proper band alignment across the heterointerface and the negative band edge movement of TiO2. The PCE of CuInS2-based QDSSCs containing In2Se3 interfacial buffer layers was 1.35%, with JSC=5.83 mA/cm2, VOC=595 mV, and FF=39.0%. We also examined the use of alternative CdS and CdSe hybrid-sensitized layers, which were sequentially deposited onto the In2Se3/CuInS2 configuration for creating favorable cascaded energy-gap structures. Both JSC (11.3 mA cm(-2)) and FF (47.3%) for the CuInS2/CdSe hybrid-sensitized cells were higher than those for CuInS2-based cells (JSC=5.83 mA cm(-2) and FF=39.0%). In addition, the hybrid-sensitized cells had PCEs that were 1.3 times those of cells containing identically pretreated In2Se3 interfacial buffer layers. Additionally, we determined that ZnSe served as a good passivation layer on the surface of CuInS2/CdSe hybrid-sensitized QDs, prevented current leakage from the QDs to electrolytes, and lowered interfacial charge recombination. Under simulated illumination (AM 1.5, 100 mW cm(-2)), multilayered QDSSCs with distinct architectures delivered a maximum external quantum efficiency of 80% at 500 nm and a maximum PCE of 4.55%, approximately 9 times that of QDSSCs fabricated with pristine CuInS2.

Photovoltaic property of a vertically aligned carbon nanotube hexagonal network assembled with CdS quantum dots

A vertically aligned carbon nanotube (VACNT) hexagonal network was fabricated by plasma enhanced chemical vapor deposition as an electrode scaffold to assemble CdS quantum dots (QDs). The quantum dot sensitized solar cell (QDSSC) based on a VACNT/CdS hexagonal network shows a short circuit current density of 4.7 mA/cm(2), which is almost twice of that based on screen-printed CNT/CdS thin film with the same thickness. The enhancement of the short circuit current could be attributed to the unique morphology of the VACNT hexagonal network, which provides direct and percolating pathways for the electrons to transfer, enhances the spectral transmission through the hexagonal microchannels to the photoactive QD sites, and also presents more surface area to assembled CdS QDs without consuming extra substrate space. The photovoltaic property of the VACNT/CdS hexagonal network indicates its potential application in the energy conversion devices.