Conduction Band Of CdS Research Articles

CdS QDs interspersed onto MOF-808 as adsorptive photocatalyst for efficient visible-light driven degradation of ciprofloxacin

CdS Quantum dots (QDs) anchored onto the surface of MOF-808 (hereafter designated as CdS QDs@MOF-808) were constructed by solvothermal method and applied for degradation of ciprofloxacin (CIP) under visible light irradiation. The impacts of pH values and initial concentrations of CIP on adsorption and photocatalytic activity were explored in detail. The as-prepared CdS QDs@MOF-808 composites showed enhanced synergistic adsorption capacity and photocatalytic properties, especially for the CM-20 sample with 20 % CdS QDs loading exhibiting about 5.2 times adsorption capacity (130 mg/g) and approximately 5.5 times photocatalytic removal rate ( 82 %) for CIP compared with the pristine CdS and MOF-808. Various techniques such as XPS, UV‐vis DRS, Zeta potential, EIS, PL as well as transient photocurrent responses have demonstrated that the synergistic effect of CdS QDs and MOF-808 is ascribed to the enhanced electrostatic interactions and Zr-S forces, improving the utilization of visible light and effectively photogenerated electrons transported from the conduction band of CdS to that of MOF-808. Gas chromatography-mass spectroscopy (GC-MS) was used to detect the possible intermediates in the degradation process of CIP.

Phase-Controlled Multi-Dimensional-Structure SnS/SnS2/CdS Nanocomposite for Development of Solar-Driven Hydrogen Evolution Photocatalyst.

The quest for water-splitting photocatalysts to generate hydrogen as a clean energy source from two-dimensional (2D) materials has enormous implications for sustainable energy solutions. Photocatalytic water splitting, a major field of interest, is focused on the efficient production of hydrogen from renewable resources such as water using 2D materials. Tin sulfide and tin disulfide, collectively known as SnS and SnS2, respectively, are metal sulfide compounds that have gained attention for their photocatalytic properties. Their unique electronic structures and morphological characteristics make them promising candidates for harnessing solar energy for environmental and energy-related purposes. CdS/SnS/SnS2 photocatalysts with two Sn phases (II and IV) were synthesized using a solvothermal method in this study. CdS was successfully placed on a broad SnS/SnS2 plane after a series of characterizations. We found that it is composited in the same way as a core-shell shape. When the SnS/SnS2 phase ratio was dominated by SnS and the structure was composited with CdS, the degradation efficiency was optimal. This material demonstrated high photocatalytic hydrogenation efficiency as well as efficient photocatalytic removal of Cr(VI) over 120 min. Because of the broad light absorption of CdS, the specific surface area, which is the reaction site, became very large. Second, it served as a transport medium for electron transfer from the conduction band (CB) of the SnS to the CB of the SnS2. Because of the composite, these electrons flowed into the CB of CdS, improving the separation efficiency of the photogenerated carriers even further. This material, which was easily composited, also effectively prevented mineral corrosion, which is a major issue with CdS.

In Situ Fabrication of CdS/Cd(OH)2 for Effective Visible Light-Driven Photocatalysis.

Photocatalytic hydrogen production is a promising technology that can generate renewable energy. However, light absorption and fast electron transfer are two main challenges that restrict the practical application of photocatalysis. Moreover, most of the composite photocatalysts that possess better photocatalytic performance are fabricated by various methods, many of which are complicated and in which, the key conditions are hard to control. Herein, we developed a simple method to prepare CdS/Cd(OH)2 samples via an in situ synthesis approach during the photocatalytic reaction process. The optimal hydrogen generation rate of CdS/Cd(OH)2 that could be obtained was 15.2 mmol·h-1·g-1, greater than that of CdS, which generates 2.6 mmol·h-1·g-1 under visible light irradiation. Meanwhile, the CdS-3 sample shows superior HER performance during recycling tests and exhibits relatively steady photocatalytic performance in the 10 h experiment. Expanded absorption of visible light, decreased recombination possibility for photo-induced carriers and a more negative conduction band position are mainly responsible for the enhanced photocatalytic hydrogen evolution performance. Photo-induced electrons will be motivated to the conduction band of CdS under the irradiation of visible light and will further transfer to Cd(OH)2 to react with H+ to produce H2. The in situ-formed Cd(OH)2 could effectively facilitate the electron transfer and reduce the recombination possibility of photo-generated electron-hole pairs.

Constructing Spatially Separated Cage-Like Z-scheme Heterojunction Photocatalyst for Enhancing Photocatalytic H2 Evolution.

Heterojunctions coupled into micro-mesoscopic structures is an attractive strategy to optimize the light harvesting and carrier separation of semiconductor photocatalysts. A self-templating method of ion exchange is reported to synthesize an exquisite hollow cage-structured Ag2 S@CdS/ZnS that direct Z-scheme heterojunction photocatalyst. On the ultrathin shell of the cage, Ag2 S, CdS, and ZnS with Zn-vacancies (VZn ) are arranged sequentially from outside to inside. Among them, the photogenerated electrons are excited by ZnS to the VZn energy level and then recombine with the photogenerated holes that are generated by CdS, while the electrons remained in the CdS conduction band are further transferred to Ag2 S. The ingenious cooperation of the Z-scheme heterojunction with the hollow structure optimizes the photogenerated charges transport channel, spatially separated the oxidation and reduction half-reactions, decreases the charge recombination probability, and simultaneously improves the light harvesting efficiency. As a result, the photocatalytic hydrogen evolution activity of the optimal sample is 136.6 and 17.3 times higher than that of cage-like ZnS with VZn and CdS by, respectively. This unique strategy demonstrates the tremendous potential of the incorporation of heterojunction construction to morphology design of photocatalytic materials, and also provided a reasonable route for designing other efficient synergistic photocatalytic reactions.

Tunable Selectivity of Photocatalytic Benzyl Alcohol Transformation over Ag-Ion-Exchanged CdS Nanowires

Existing methods for the photocatalytic transformation of aromatic alcohols to value-added products via C–C cross-coupling are inefficient and insufficiently selective. Herein, a series of cadmium sulfide nanowires (CdS NWs) loaded with Ag2S (denoted as Ag2S@CdS NWs) are constructed via a simple Ag+ exchange protocol for the photocatalytic transformation of benzyl alcohol. We successfully demonstrated that the selectivity toward specific products in the photocatalytic transformation of benzyl alcohol over Ag+-exchanged CdS NWs is controlled by varying the amount of exchanged Ag+ ions. Notably, the product of the photocatalytic reaction was dependent on the amount of Ag+ ions exchanged: with a Ag+ exchange of <5 mol %, the C–C coupling product was obtained with >90% selectivity and >95% transformation yield owing to photoinduced electron transfer from the conduction band of CdS to Ag2S. Conversely, with a Ag+ exchange of >7 mol %, a cocatalyst in which Ag2S and Ag are mixed was produced, and benzaldehyde was obtained with >90% selectivity and >90% transformation yield because of photoinduced hole transfer from the valence band of CdS to Ag2S/Ag. This study proves that Ag2S@CdS NWs can be used as a basis for the development of heterojunction photocatalysts for the conversion of aromatic alcohols into value-added products via C–C cross-coupling reactions or photooxidation toward aromatic aldehyde.

Enhancement of opto-electrical properties in Co doped CdS–TiO2 nanocomposite thin film as photoanode for Semiconductor Sensitized Solar Cells (SSSCs)

Cobalt doped CdS–TiO 2 nanocomposite thin films were coated on glass substrates by bottom up approaching methods. ZnS nanolayer over cobalt doped CdS–TiO 2 films act as a protective layer of CdS nanocrystal which enhances the photo stability. The structural, optical, electrical and surface morphological properties of ZnS-cobalt CdS–TiO 2 composite thin film were systematically evaluated. Structural analysis indicates that Co 2+ ions have been successfully incorporated in CdS site. The doping of cobalt in ZnS–CdS–TiO 2 film gives rise to an increase in the lattice parameter while the band gap decreased with increasing cobalt concentration. The bandgap of doped film decreases indicating the easy way of electron transfer from valence band to conduction band of CdS and TiO 2 . Surface morphological studies shows the diffusion of cobalt doped CdS nanoparticles into TiO 2 nanoporous structure of the composite film . The emission peaks in photoluminescence spectrum of ZnS-cobalt CdS–TiO 2 film proved the clear interaction of cobalt dopant with CdS nanocrystals. An enhancement in conductivity was observed due to incorporation of cobalt in CdS site and the resistance value (∼47%) was significantly decreased for cobalt doped CdS under illumination condition. Electrical analysis proved that the doped film is preferred as conductive electrode in solar cells than undoped film. • Cobalt doped CdS–TiO 2 composite thin films were synthesized by simple wet chemical method. • Interlocked CdS nanocrystals observed in SEM analysis, facilitate easy penetration into TiO 2 nanoporous structure of the composite film. • The doped film exhibit shifting of absorption edge towards longer wavelength (red shift), indicates decreased optical band gap. • The doped film shows superior electrical performance due to decreased resistance, preferred as conductive electrode in solar cells.

Modulation of the Band Bending of CdS by Fluorination to Facilitate Photoinduced Electron Transfer for Efficient H2 Evolution over Pt/CdS

The potential barrier (Schottky barrier), embodied in the upward band bending of an n-type semiconductor at the interface of a Pt-loaded semiconductor, often makes it difficult for the interfacial photoinduced electron transfer from the conduction band of the semiconductor to the loaded Pt, giving rise to the recombination probability of the photogenerated charges. In this work, we prepared fluorinated CdS by a facile hydrothermal process in the presence of NH4F. With the assistance of the noble metal Pt, the fluorinated CdS exhibits a superior photocatalytic H2 evolution to pristine CdS. Various characterization results revealed that the incorporation of the fluorine anions into the CdS lattice by fluorination apparently lowers the Fermi level to weaken the upward band bending of CdS at the Pt/CdS interface, favoring the interfacial photoinduced electron transfer from the conduction band of CdS to the loaded Pt for an efficient H2 evolution. This work highlights the role of weakening the potential barrier at the Pt/CdS interface in promoting the interfacial photoinduced electron transfer for efficient H2 evolution.

Slow Auger Recombination of Trapped Excitons Enables Efficient Multiple Electron Transfer in CdS-Pt Nanorod Heterostructures.

Solar-to-fuel conversion reaction often requires multiple proton-coupled electron transfer (PCET) processes powered by the energetic electrons and/or holes generated by the absorption of multiple photons. The effective coupling of multiple electron transfer from the light absorber with the multiple PCET reactions at the catalytic center is one of the key challenges in efficient and selective conversion of solar energy to chemical fuels. In this paper, we examine the dynamics of multiple electron transfer in quantum confined CdS nanorods with a Pt tip, in which the CdS rod functions as the light absorber and the Pt tip the catalytic center. By excitation-fluence-dependent transient absorption spectroscopic measurements, we show that the multiexciton Auger recombination rate in CdS rods follows a carrier-collision model, knA = n2(n - 1)/4k2A, with a biexciton lifetime (1/k2A) of 2.0 ± 0.2 ns. In CdS-Pt nanorods, electron transfer kinetics from the CdS conduction band edge to the Pt show negligible dependence on the excitation fluence, occurring with a half-life time of 5.6 ± 0.6 ps. The efficiency of multiple exciton dissociation by multiple electron transfer to Pt decreases from 100% in biexciton states to ∼41% at 22 exciton state due to the competition with Auger recombination. The half-lifetime of the n-charge separated state recombination (with n electrons in the Pt and n holes in the CdS) decreases from 10 μs in the single charge separated state to 42 ns in nine charge separated states. Our findings suggest the possibility of driving multielectron photocatalytic reactions under intense illumination and controlling product selectivity through multielectron transfer.

Photocatalytic Penicillin Degradation Performance and the Mechanism of the Fragmented TiO2 Modified by CdS Quantum Dots.

In this study, a novel method was adopted to construct a CdS–TiO2 heterostructure to degrade penicillin under sunlight. A potato extract was used during the synthesis process of CdS QDs as a stabilizer and a modifier. The CdS–TiO2 composite with a heterostructure delivers high photocatalytic degradation efficiency. In detail, 0.6 mg/mL of CdS–TiO2 can successfully decompose penicillin after 2 h, and 5‰ CdS–TiO2 shows the optimal degradation efficiency with the degradation rate reaching 88%. Furthermore, the underlying mechanisms of the penicillin decomposition reaction were investigated by the EPR test and trapping experiment. It was found that the high photocatalytic degradation efficiency was attributed to the heterojunction of CdS–TiO2, which successfully suppresses the recombination of the conduction band of CdS and the valence band of TiO2. Moreover, it was confirmed that the reaction is the O2-consuming process, and introducing O2 can greatly accelerate the generation of a superoxide radical during the photocatalytic degradation process, which eventually improves the degradation of penicillin and shortens the degradation time. Finally, this work provides the possible penicillin degradation pathways, which will inspire the researchers to explore and design novel photocatalysts in the field of wastewater treatment in the future.

CdS nanorods supported copper-nickel hydroxide for hydrogen production under direct sunlight irradiation

A series of composite photocatalysts based on CdS nanorods decorated with Cu/Ni hydroxides were prepared via deposition precipitation method at room temperature (total metal loading ≈ 3 wt%). The performance of these photocatalysts was evaluated for H2 production through water dissociation reaction under direct sunlight. The 2.4Cu(OH)20.6Ni(OH)2/CdS photocatalyst with a total 3 wt% nominal metal cocatalyst loading demonstrated an excellent hydrogen production activity of ~20 mmol h−1g−1, that is 2 and 20 times greater than the benchmark Au/CdS and pristine CdS photocatalysts, respectively. Detailed analyses based on UV–Visible diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), steady state photoluminescence (PL) and energy dispersive spectroscopy (EDS) suggested cocatalysts Cu/Ni hydroxides were transformed into their metallic states during photoreaction. Cu° was produced by the transfer of electrons due to the as available position of CdS conduction band (E°=0.61 V) to surface Cu(OH)2 nanoclusters (Cu(OH)2/Cu°, E°= 0.224 V) whereas Ni° was produced by the shift in conduction band level of CdS under continuous sunlight illumination (Ni(OH)2/Ni°, E°= 0.72 V). Based on these observations, the mechanism of hydrogen production from water splitting over Cu/Ni(hydroxides)-CdS was described.

Blue-light photoelectrochemical aptasensor for kanamycin based on synergistic strategy by Schottky junction and sensitization

The sensitive, selective, and accurate analysis of kanamycin (KAN), a common aminoglycoside antibiotic, is vital to ensure human health and food safety. Here, a well-designed photoelectrochemical (PEC) KAN aptasensor was proposed based on the synergistic strategy by Schottky junction and sensitization. A Schottky junction of CuO/Pd nanocomposite was used as a PEC substrate to immobilize an aptamer. The Schottky barrier not only provided an electron-transfer irreversible passage from CuO to Pd shell but also generated a local surface plasmon resonance between CuO and Pd shell, thus improving the efficient charge separation and light absorption. Complementary-DNA-functionalized CdS quantum dots (CdS QDs) were introduced onto the surface of CuO/Pd via hybridization of the target aptamer to improve the response of the PEC aptasensor further. When CdS was close to Pd shell, the Fermi energy level of CdS was readjusted under the action of the sensitization. The photogenerated hot electrons on the conduction band of CdS were transferred into Pd by a powerful interfacial electric field. Upon blue-light irradiation, the change of photocurrent depended upon the amount of stored negative charge on the surface of the Pd shell and stored positive charge on the valence band of CdS before and after incubation with KAN. Using the photocurrent change as a response signal for the quantitative detection of KAN, the PEC aptasensor exhibited a low detection limit of 20 pM with a wide linear range of 0.1–500 nM. Thus, the developed PEC aptasensor has great potential for applications in various fields.

Synthesis and characterization of successive Z-scheme CdS/Bi2MoO6/BiOBr heterojunction photocatalyst with efficient performance for antibiotic degradation

A novel CdS/Bi 2 MoO 6 /BiOBr successive Z-scheme photocatalyst has been synthesized by a solvothermal-precipitation method. The structure, composition, morphology and optical property of the ternary composite were investigated. The maximum degradation rate of CdS/Bi 2 MoO 6 /BiOBr for tetracycline hydrochloride (TC) can reach 94.41% under visible light, while its degradation rate was 10.43, 2.89, and 2.43 times higher than that of pure Bi 2 MoO 6 , BiOBr and Bi 2 MoO 6 /BiOBr, respectively. Besides, the CdS/Bi 2 MoO 6 /BiOBr composite showed stable catalytic performance after three successive reuses. The improved photocatalytic and stability could be ascribed to the extended visible-light absorption capability, effective separation of electron-hole pairs and layered stable structure. Photoluminescence spectroscopy and electrochemical impedance spectroscopy proved that the composite had more efficient charge separation efficiency. The energy band structure and free radical capturing experiments proved that the redox reaction mainly occurred in the conduction band of CdS and the valence band of BiOBr in this composite, so a possible successive Z-scheme heterojunction mechanism is proposed. This work also provides a feasible idea for the treatment of TC in wastewater. A novel CdS/Bi 2 MoO 6 /BiOBr heterojunction photocatalyst, with high catalytic activity for tetracycline hydrochloride (TC), was synthesized and evaluated. Notably, this ternary composite showed higher degradation rate pure Bi 2 MoO 6 , BiOBr and CdS. Based on the characterization results, the possible mechanism of electron transmission was proposed. • A novel CdS/Bi 2 MoO 6 /BiOBr photocatalyst was synthesized with successive heterojunction. • CdS/Bi 2 MoO 6 /BiOBr has good catalytic activity for tetracycline hydrochloride. • The catalyst has a good separation efficiency of photogenerated electron-hole pairs. • The catalyst shows excellent cycle stability.

Integrating the plasmonic sensitizer and electron relay into ZnO/Au/CdS sandwich nanotube array photoanode for efficient solar-to-hydrogen conversion with 3.2% efficiency

Herein, both plasmonic sensitizer and electron relay are integrated into ZnO/Au/CdS sandwich nanotube array (NTA) to construct a novel photoanode for efficient solar-to-hydrogen conversion via photoelectrochemical (PEC) cell. Under bias-free simulated solar light illumination, a photocurrent of the ZnO/Au/CdS sandwich NTA photoanode is up to 6.5 mA/cm2, 24 times that of ZnO, and 14 times that of ZnO/Au NTA photoanodes, respectively. Furthermore, the highest solar-to-hydrogen efficiency of the ZnO/Au/CdS sandwich NTA photoanode is 3.2% at 0.72 eV vs. RHE, 23 times as high as that of ZnO/Au and 80-folds that of the pure ZnO NTA photoanodes, respectively. The PEC and photoluminescence measurements experimentally demonstrate that the Aunanoparticles not only serve as plasmonic sensitizer to efficiently transfer the electrons from the defect level of ZnO to its conduction band via resonance coupling action of the plasmon and defect energy emission, but also serve as electron relay to transfer the electrons from the conduction band of CdS to that of ZnO, enabling the ZnO/Au/CdS sandwich NTAs to achieve greatly enhanced PEC water splitting activity. This work offers a new strategy for integrating both plasmonic sensitizer and electron relay into a photoanode for efficient conversion of solar energy to chemical energy.

Graphene-Amplified Photoelectric Response of CdS Nanoparticles for Cu2+ Sensor.

Graphene/CdS composites were synthesized through the direct deposition of CdS nanoparticles on graphene sheets. The high conductivity of graphene sheets and the intimate heterointerfacial connection between graphene sheets and CdS nanoparticles provided prominent advantages for enhancing light absorption and facilitating the transfer of photogenerated carriers from CdS nanoparticles, thus leading to an effectively separation of electron-hole pairs and consequently an improvement in photocurrent intensity. A highly sensitive and selective photoelectrochemical sensor for detecting copper ions (Cu2+) was developed based on the interaction between Cu2+ and CdS by forming CuxS-coated CdS nanoparticles, which serves as the recombination centers, impedes the transfer of electron from the conduction band of CdS to graphene sheets, and consequently leads to a decrease in photocurrent intensity. The sheets not only effectively transferred the photogenerated electrons deriving from CdS nanoparticles but also resulted in an enhancement in photocurrent intensity in the presence of various metal ions except Cu2+. The sheets amplified the photoelectric response of CdS semiconductor for Cu2+ sensing, in which the photocurrent intensity decreased dramatically.

Novel photocatalyst incorporating Ni-Co layered double hydroxides with P-doped CdS for enhancing photocatalytic activity towards hydrogen evolution

Designing durable and highly active photocatalysts for hydrogen evolution via water splitting is still very challenging. Novel NiCo-LDH/P-CdS hybrid photocatalysts are fabricated by combining strategies of P-doping and in-situ loading of NiCo-LDH. P-doping creates a mid-gap at the bottom of the conduction band of CdS, which facilitates to prolong the life-time of the photo-induced electrons. Subsequently, the in-situ loading of NiCo-LDH is able to form heterojunctions between NiCo-LDH and P-CdS that not only promote the separation efficiency of carriers, but also effectively reduce the light corrosion phenomenon commonly observed in CdS. The as-prepared 2 mol% NiCo-LDH/40 wt% P-CdS sample shows a high visible-light catalytic H2 production rate of 8.665 mmol·h−1 g−1, which is 45 times higher than pure CdS. The apparent quantum yield is determined to be 14.0% at 420 nm monochromatic light. Based on the calculation of density function theory (DFT), the rational photocatalytic mechanism has been proposed and is well consistent with the experimental results. Our study not only demonstrates a facile, eco-friendly and scalable strategy to synthesize highly efficient photocatalysts, but also provides a new viewpoint of the rational design and synthesis of advanced photocatalysts by harnessing the strong synergistic effects through simultaneously tuning and optimizing the electronic structure and surface.

Citric Acid Capped CdS Quantum Dots for Fluorescence Detection of Copper Ions (II) in Aqueous Solution.

Citric acid capped CdS quantum dots (CA-CdS QDs), a new assembled fluorescent probe for copper ions (Cu2+), was synthesized successfully by a simple hydrothermal method. In this work, the fluorescence sensor for the detection of heavy and transition metal (HTM) ions has been extensively studied in aqueous solution. The results of the present study indicate that the obtained CA-CdS QDs could detect Cu2+ with high sensitivity and selectivity. It found that the existence of Cu2+ has a significant fluorescence quenching with a large red shifted (from greenish-yellow to yellowish-orange), but not in the presence of 17 other HTM ions. As a result, Cu2S, the energy level below the CdS conduction band, could be formed at the surface of the CA-CdS QDs and leads to the quenching of fluorescence of CA-CdS QDs. Under optimal conditions, the copper ions detection range using the synthesized fluorescence sensor was 1.0 × 10‒8 M to 5.0 × 10‒5 M and the limit of detection (LOD) is 9.2 × 10‒9 M. Besides, the as-synthesized CA-CdS QDs sensor exhibited good selectivity toward Cu2+ relative to other common metal ions. Thus, the CA-CdS QDs has potential applications for detecting Cu2+ in real water samples.

Highly efficient visible-light driven solar-fuel production over tetra(4-carboxyphenyl)porphyrin iron(III) chloride using CdS/Bi2S3 heterostructure as photosensitizer

Fabrication of hybrid system coupling inorganic semiconductor photosensitizer with molecular catalyst provides a promising approach to achieve highly efficient CO2 reduction into solar fuels, as the semiconductor nanomaterials can meet the prerequisites of visible-light photoresponse and high charge-separation efficiency for achieving high photocatalytic efficiency. In this work, CdS/Bi2S3 heterostructures have been prepared via an ion-exchange reaction and employed as the photosensitizer to couple with tetra(4-carboxyphenyl)porphyrin iron(III) chloride (FeTCPP) molecular catalyst for photoreduction of CO2 into CO and H2 under visible-light irradiation. The sulfur vacancy in CdS surface can be reduced by the formation of CdS/Bi2S3 heterostructure. The content of Bi2S3 can be modulated via tailoring the ion-exchange reaction time. The resulting effect on the performace of CO2 photoreduction has been investigated in detail. Benefiting from the enhanced separation and utilization of charge carriers, CdS/Bi2S3-0.5 h/FeTCPP hybrid catalyst exhibits 8.2 times CO yield (1.93 mmol/g/h) and 1.7 times H2 yield (6.08 mmol/g/h) of CdS/FeTCPP hybrid catalyst. More important, the results of energy level alignment, electron spin resonance and photocatalysis indicate that electron-transfer direction can be changed once the CdS/Bi2S3 heterostructure is coupled with FeTCPP. In the CdS/Bi2S3 heterostructure, electrons transfer mainly from the conduction band of CdS to Bi2S3, while it is mainly from the conduction band of CdS to FeTCPP in the CdS/Bi2S3/FeTCPP hybrid.

Enhanced photoconductivity in CdS/betanin composite nanostructures.

Development of novel materials for thin film solar cells are gaining significant attention due to their tunable wide bandgap and extensive application potential in flexible energy harvesters. CdS is a known window material for thin film solar cells. Tuning of the photoconductivity of CdS by doping, substitution and grain size tailoring is widely attempted by researchers. Inorganic core/shell structures like CdS/CdSe, CdS/ZnS etc. are other possible candidates with band gap tailorability. However, such attempts are rare in tailoring the photoconductivity by providing an organic shell over the inorganic core. Here the authors synthesised CdS/betanin core/shell structures using wet chemical routes. Spectroscopic studies show that the composite structure is core/shell like, with CdS as the core and betanin (a natural dye), as the outer shell with an average core particle size of 10 nm. The absorption spectra of the composite system show the signature of an additional band in the lower wavelength region and it is redshifted with increase in betanin percentage. The intermediate band observed in the energy of ∼1.75 eV, helps CdS to enhance the rate of absorption. Simultaneous absorbance of lower and higher energy photons from the solar radiation can increase the efficiency of CdS based solar cells. A huge enhancement in conductivity is observed in CdS/betanin composites on illumination with white light due to the transfer of photogenerated electrons from the conduction band of betanin dye to the conduction band of CdS.

Surface step decoration of isolated atom as electron pumping: Atomic-level insights into visible-light hydrogen evolution

Here we realize the decoration of isolated platinum atoms onto the surface step of CdS nanowires. The single-atom co-catalyst with high stability can realize maximum atom efficiency and significantly boost electron-hole separation efficiency in chromophore units, generating a greatly enhanced photocatalytic hydrogen evolution performance, 7.69 times as high as Pt nanoparticles do and 63.77 times higher than that of bare CdS nanowires. Directional migrations of photogenerated excitons from the conduction band of CdS to catalytic platinum centers have been witnessed by transient absorption spectroscopy, leading to the supply of long-lived electrons for highly efficient photocatalytic hydrogen evolution. Density functional theory calculations further confirm that the excellent catalytic performance is associated with positively charged platinum sites with partially vacant 5d orbitals, which change distribution of charge density and facilitate higher excited carrier density.

Influences of donor defect passivation on the performance of Cu(In,Ga)Se2 thin-film solar cell

In this work, the study of donor defect passivation in CIGS solar cell was simulated by wxAMPS software. The effects of near-interface shallow donor defect and bulk donor defect on the performances of solar cell were investigated mainly through changing the state densities and their position distributions. The results show that the high density of the near-interface shallow donor defect state decreases the open circuit voltage. By contrast, the low density of the near-interface shallow donor defect state has the higher open circuit voltage and short-circuit current density. But it easily leads to the CdS conduction band offset increased, then raising carrier recombination rate which decreases the fill factor. For the passivation of the bulk donor defect in the absorption layer, the performances of the CIGS solar cell are much dependent on the position distribution of donor defect state density. Among them, the decrease of the state density in the space charge region can improve the open-circuit voltage. Meanwhile, the reduction of the state density in the quasi-neutral region can increase the short-circuit current density. With the bulk donor defect state density decreased, the conversion efficiency will saturate due to the limitation of the acceptor concentration. When the donor defect state density is low enough, the influence of capture cross section on the device performance is reduced. The conversion efficiencies varying with passivation region were compared from two directions (CdS to Mo and Mo to CdS). It was found the passivation of the donor defect in the transition region where the position from the quasi-neutral region to the space charge region in the absorption was critical to the improvement in the conversion efficiency of the solar cell under a suitable alkali element concentration.