Beyond Photovoltaics: Semiconductor Nanoarchitectures for Liquid-Junction Solar Cells

Perovskite Photovoltaic Integrated CdS/TiO2 Photoanode for Unbiased Photoelectrochemical Hydrogen Generation

Photoelectrolysis of water using solar energy into storable and environment-friendly chemical fuel in the form of hydrogen provides a potential solution to address the environmental concerns and fulfill future energy requirements in a sustainable manner. Achieving efficient and spontaneous hydrogen evolution in water using solar light as the only energy input is a highly desirable but a difficult target. In this work, we report perovskite solar cell integrated CdS-based photoanode for unbiased photoelectrochemical hydrogen evolution. An integrated tandem device consisting of mesoporous CdS/TiO₂ photoanode paired with a triple-cation perovskite (Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃) solar cell is developed via a facile fabrication route. The proposed photovoltaic integrated photoanode presents an efficient tandem configuration with high optical transparency to long-wavelength photons and strong photoelectrochemical conversions from short-wavelength photons. On the basis of this integrated tandem device, an unbiased photocurrent density of 7.8 mA/cm² is demonstrated under AM1.5G illumination.

Hybrid PbS Quantum-Dot-in-Perovskite for High-Efficiency Perovskite Solar Cell

In this study, a facile and effective approach to synthesize high-quality perovskite-quantum dots (QDs) hybrid film is demonstrated, which dramatically improves the photovoltaic performance of a perovskite solar cell (PSC). Adding PbS QDs into CH3 NH3 PbI3 (MAPbI3 ) precursor to form a QD-in-perovskite structure is found to be beneficial for the crystallization of perovskite, revealed by enlarged grain size, reduced fragmentized grains, enhanced characteristic peak intensity, and large percentage of (220) plane in X-ray diffraction patterns. The hybrid film also shows higher carrier mobility, as evidenced by Hall Effect measurement. By taking all these advantages, the PSC based on MAPbI3 -PbS hybrid film leads to an improvement in power conversion efficiency by 14% compared to that based on pure perovskite, primarily ascribed to higher current density and fill factor (FF). Ultimately, an efficiency reaching up to 18.6% and a FF of over ≈0.77 are achieved based on the PSC with hybrid film. Such a simple hybridizing technique opens up a promising method to improve the performance of PSCs, and has strong potential to be applied to prepare other hybrid composite materials.

Comparison of Phonon Damping Behavior in Quantum Dots Capped with Organic and Inorganic Ligands

Surface ligand modification of colloidal semiconductor nanocrystals has been widely used as a means of controlling photoexcited-state generation, relaxation, and coupling to the environment. While progress has been made in understanding how surface ligand modification affects the behavior of electronic states, less is known about the influence of surface ligand modification on phonon behavior, which impacts relaxation dynamics and transport phenomena. In this work, we compare the dynamics of optical and acoustic phonons in CdTe quantum dots (QDs), CdTe/CdSe core/shell QDs capped with octadecylphosphonic acid ligands, and CdTe QDs capped with Se^2- to ascertain how ligand exchange from native aliphatic ligands to single-atom Se^2- ligands affects phonon behavior. We use transient absorption spectroscopy and observe modulations in the kinetics of excited-state decay due to QD lattice vibrations from both optical and acoustic phonons, which we describe using the damped oscillator model. The longitudinal optical phonons have similar frequencies and damping behavior in all three samples. In contrast, the longitudinal acoustic phonon mode in the Se^2--capped CdTe QDs is severely damped, much more so than in CdTe and CdTe/CdSe QDs capped with the native aliphatic ligands. We attribute these differences in the acoustic phonon behavior to the differences in how the QD dissipates vibrational energy to its surroundings as a function of ligand identity. Our results indicate that these inorganic surface-capping ligands enhance not only the electronic but also the mechanical coupling of nanocrystals with their environment.

Nanoarchitectures in dye-sensitized solar cells: metal oxides, oxide perovskites and carbon-based materials

Dye-sensitized solar cells (DSSCs) have aroused great interest and been regarded as a potential renewable energy resource among the third-generation solar cell technologies to fulfill the 21^st century global energy demand. DSSCs have notable advantages such as low cost, easy fabrication process and being eco-friendly in nature. The progress of DSSCs over the last 20 years has been nearly constant due to some limitations, like poor long-term stability, narrow absorption spectrum, charge carrier transportation and collection losses and poor charge transfer mechanism for regeneration of dye molecules. The main challenge for the scientific community is to improve the performance of DSSCs by using different approaches, like finding new electrode materials with suitable nanoarchitectures, dyes in composition with promising semiconductors and metal quantum dot fluorescent dyes, and cost-effective hole transporting materials (HTMs). This review focuses on DSSC photo-physics, which includes charge separation, effective transportation, collection and recombination processes. Different nanostructured materials, including metal oxides, oxide perovskites and carbon-based composites, have been studied for photoanodes, and counter electrodes, which are crucial to achieve DSSC devices with higher efficiency and better stability.

Toxicity of engineered nanomaterials mediated by nano-bio-eco interactions

Engineered nanomaterials may adversely impact human health and environmental safety by nano-bio-eco interactions not fully understood. Their interaction with biotic and abiotic environments are varied and complicated, ranging from individual species to entire ecosystems. Their behavior, transport, fate, and toxicological profiles in these interactions, addressed in a pioneering study, are subsequently seldom reported. Biological, chemical, and physical dimension properties, the so-called multidimensional characterization, determine interactions. Intermediate species generated in the dynamic process of nanomaterial transformation increase the complexity of assessing nanotoxicity. We review recent progress in understanding these interactions, discuss the challenges of the study, and suggest future research directions.

Electrocatalytic and photocatalytic hydrogen evolution integrated with organic oxidation

We have summarized the recent progress in electrocatalytic and photocatalytic water splitting integrated with organic oxidation for efficient H₂ generation, which features no formation of explosive H₂/O₂ mixtures and reactive oxygen species, higher efficiency compared to conventional water splitting and potential co-production of value-added organic products.

Enhanced light-harvesting by plasmonic hollow gold nanospheres for photovoltaic performance

A 'sandwich'-structured TiO₂NR/HGN/CdS photoanode was successfully fabricated by the electrophoretic deposition of hollow gold nanospheres (HGNs) on the surface of TiO₂ nanorods (NRs). The HGNs presented a wide surface plasmon resonance character in the visible region from 540 to 630 nm, and further acted as the scatter elements and light energy 'antennas' to trap the local-field light near the TiO₂NR/CdS layer, resulting in the increase of the light harvesting. An outstanding enhancement in the photochemical behaviour of TiO₂NR/HGN/CdS photoanodes was attained by the contribution of HGNs in increasing the light absorption and the number of electron-hole pairs of photosensitive semiconductors. The optimized photochemical performance of TiO₂NR/HGN/CdS photoanodes by using plasmonic HGNs demonstrated their potential application in energy conversion devices.

Quantum dot-sensitized solar cells

A comprehensive overview of the development of quantum dot-sensitized solar cells (QDSCs) is presented.

Temperature dependent excited state dynamics in dual emissive CdSe nano-tetrapods

Excited state dynamics of dual emissive CdSe nano-tetrapods has been studied over several decades of time and broad range of temperature.

Comparative advantages of Zn–Cu–In–S alloy QDs in the construction of quantum dot-sensitized solar cells

Alloyed structures of quantum dot light-harvesting materials favor the suppression of unwanted charge recombination as well as acceleration of the charge extraction and therefore the improvement of photovoltaic performance of the resulting solar cell devices. Herein, the advantages of Zn–Cu–In–S (ZCIS) alloy QD serving as light-harvesting sensitizer materials in the construction of quantum dot-sensitized solar cells (QDSCs) were compared with core/shell structured CIS/ZnS, as well as pristine CIS QDs. The built QDSCs with alloyed Zn–Cu–In–S QDs as photosensitizer achieved an average power conversion efficiency (PCE) of 8.47% (V_oc = 0.613 V, J_sc = 22.62 mA cm⁻², FF = 0.610) under AM 1.5G one sun irradiation, which was enhanced by 21%, and 82% in comparison to those of CIS/ZnS, and CIS based solar cells, respectively. In comparison to cell device assembled by the plain CIS and core/shell structured CIS/ZnS, the enhanced photovoltaic performance in ZCIS QDSCs is mainly ascribed to the faster photon generated electron injection rate from QD into TiO₂ substrate, and the effective restraint of charge recombination, as confirmed by incident photon-to-current conversion efficiency (IPCE), open-circuit voltage decay (OCVD), as well as electrochemical impedance spectroscopy (EIS) measurements.

Benefiting from the accelerative electron injection and retarded charge recombination, Zn–Cu–In–S alloy QD based QDSC achieved a PCE of 8.55%, which is 21%, and 82% higher than those of CIS/ZnS, and pristine CIS QDs based solar cells, respectively.

Absolute Energy Level Positions in CdSe Nanostructures from Potential-Modulated Absorption Spectroscopy (EMAS)

Semiconductor nanostructures such as CdSe quantum dots and colloidal nanoplatelets exhibit remarkable optical properties, making them interesting for applications in optoelectronics and photocatalysis. For both areas of application a detailed understanding of the electronic structure is essential to achieve highly efficient devices. The electronic structure can be probed using the fact that optical properties of semiconductor nanoparticles are found to be extremely sensitive to the presence of excess charges that can for instance be generated by means of an electrochemical charge transfer via an electrode. Here we present the use of EMAS as a versatile spectroelectrochemical method to obtain absolute band edge positions of CdSe nanostructures versus a well-defined reference electrode under ambient conditions. In this, the spectral properties of the nanoparticles are monitored with respect to an applied electrochemical potential. We developed a bleaching model that yields the lowest electronic state in the conduction band of the nanostructures. A change in the band edge positions caused by quantum confinement is shown both for CdSe quantum dots and for colloidal nanoplatelets. In the case of CdSe quantum dots these findings are in good agreement with tight binding calculations. The method presented is not limited to CdSe nanostructures but can be used as a universal tool. Hence, this technique allows the determination of absolute band edge positions of a large variety of materials used in various applications.

Atomistic Modeling of Quantum Dots at Experimentally Relevant Scales Using Charge Equilibration

Quantum dots (QDs) have been successfully employed within a vast array of fundamental and applied studies spanning all subdisciplines of chemistry. However, ab initio models of QD behavior are inherently limited by computational cost due to the large number of atoms within QDs of experimentally relevant size. This work builds upon the method of charge equilibration (qEQ) to account for system interactions unique to QDs (QD-qEQ) and demonstrates accuracy through calculated per-QD energies and dipole moments that agree generally with ab initio calculations and experimental observation, respectively. By forgoing electronic structure information, QD-qEQ exhibits a distinct advantage in its exceptionally low computational cost, which affords consideration of over 35,000 unique spherical wurtzite CdSe structures with radii ≤12.5 Å. A comparison of QD-qEQ calculations with experimental data relating to the phenomenon of CdSe magic size crystals (MSCs) affords statistical and structural insight into why MSCs are observed. Consideration of structures ≤12.5 Å reveals QD sizes corresponding with local minima in QD energy, correlating closely with experimentally observed MSCs. The physical origin of observed energy minima is assigned to QD structures with surfaces exhibiting large fractions of highly coordinated atoms, a physical trait postulated to yield fewer reaction sites for stepwise growth, resulting in MSC stability. The low computational cost along with the per-atom and per-structure electrostatic data afforded by QD-qEQ makes this method an enticing approach to address dynamic QD behavior and enables potential applications within a broad range of fields concomitant to those in which QD inclusion has already proven useful.

Controlled synthesis of near-infrared quantum dots for optoelectronic devices

We designed a facile approach for the synthesis of PbS quantum dots (QDs) using thiourea and lead acetate as sources of sulfur and lead, respectively. The sizes of the PbS QDs could be systematically controlled by simply adjusting the reaction parameters. Cd post-treatment via a cation exchange method was performed to increase the stability of QDs. As a proof of concept, colloidal PbS QDs synthesized by using air-stable thiourea were employed as light harvesters for both (i) solar driven photoelectrochemical (PEC) hydrogen generation and (ii) QDs sensitized solar cells (QDSSCs). For PEC hydrogen generation, similar saturated photocurrent densities are observed by using thiourea compared to bis(trimethylsilyl) sulfide, which is air-sensitive and unstable. For QDSSCs, the devices fabricated with QDs synthesized from thiourea reveal a better performance compared to devices fabricated with QDs synthesized from traditional bis(trimethylsilyl) sulfide. Our work demonstrates that this synthetic method is a promising alternative to the existing methodologies of PbS QDs and holds great potential for future solar technologies.

Superior Inorganic Ion Cofactors of Tetraborate Species Attaining Highly Efficient Heterogeneous Electrocatalysis for Water Oxidation on Cobalt Oxyhydroxide Nanoparticles

A heterogeneous catalyst incorporating an inorganic ion cofactor for electrochemical water oxidation was exploited using a CoO(OH) nanoparticle layer-deposited electrode. The significant catalytic current for water oxidation was generated in a Na₂B₄O₇ solution at pH 9.4 when applying 0.94 V versus Ag/AgCl in contrast to no catalytic current generation in the K₂SO₄ solution at the same pH. HB₄O₇^- and B₄O₇^2- ions were indicated to act as key cofactors for the induced catalytic activity of the CoO(OH) layer. The Na₂B₄O₇ concentration dependence of the catalytic current was analyzed based on a Michaelis-Menten-type kinetics to provide an affinity constant of cofactors to the active sites, K_m = 28 ± 3.6 mM, and the maximum catalytic current density, I_max = 2.3 ± 0.13 mA cm^-2. The I_max value of HB₄O₇^- and B₄O₇^2- ions was 1.4 times higher than that (1.3 mA cm^-2) for the previously reported case of CO₃^2- ions. This could be explained by the shorter-range proton transfer from the active site to the proton-accepting cofactor because of the larger size and more flexible conformation of HB₄O₇^- and B₄O₇^2- ions compared with that of CO₃^2- ions.

Size dependence of efficiency of PbS quantum dots in NiO-based dye sensitised solar cells and mechanistic charge transfer investigation

Quantum dots (QDs) are very attractive materials for solar cells due to their high absorption coefficients, size dependence and easy tunability of their optical and electronic properties due to quantum confinement. Particularly interesting are PbS QDs owing to their broad spectral absorption until long wavelengths, their easy processability and low cost. Here, we used control of the PbS QD size to understand charge transfer processes at the interfaces of a NiO semiconductor and explain the optimal QD size in photovoltaic devices. Towards this goal, we have synthesized a series of PbS QDs with different diameters (2.8 nm to 4 nm) and investigated charge transfer dynamics by time resolved spectroscopy and their ability to act as sensitizers in nanocrystalline NiO based solar cells using the cobalt tris(4,4'-ditert-butyl-2,2'-bipyridine) complex as a redox mediator. We found that PbS QDs with an average diameter of 3.0 nm show the highest performance in terms of efficient charge transfer and light harvesting efficiency. Our study showed that hole injection from the PbS QDs to the NiO valence band (VB) is an efficient process even with low injection driving force (-0.3 eV) and occurs in 6-10 ns. Furthermore we found that direct electrolyte reduction (photoinduced electron transfer to the cobalt redox mediator) also occurs in parallel to the hole injection with a rate constant of similar magnitude (10-20 ns). In spite of its large driving force, the rate constant of the oxidative quenching of PbS by Co(iii) diminishes more steeply than hole injection on NiO when the diameter of PbS increases. This is understood as the consequence of increasing the trap states that limit electron shift. We believe that our detailed findings will advance the future design of QD sensitized photocathodes.

Elucidating the role of surface passivating ligand structural parameters in hole wave function delocalization in semiconductor cluster molecules

This article describes the mechanisms underlying electronic interactions between surface passivating ligands and (CdSe)₃₄ semiconductor cluster molecules (SCMs) that facilitate band-gap engineering through the delocalization of hole wave functions without altering their inorganic core. We show here both experimentally and through density functional theory calculations that the expansion of the hole wave function beyond the SCM boundary into the ligand monolayer depends not only on the pre-binding energetic alignment of interfacial orbitals between the SCM and surface passivating ligands but is also strongly influenced by definable ligand structural parameters such as the extent of their π-conjugation [π-delocalization energy; pyrene (Py), anthracene (Anth), naphthalene (Naph), and phenyl (Ph)], binding mode [dithiocarbamate (DTC, -NH-CS₂^-), carboxylate (-COO^-), and amine (-NH₂)], and binding head group [-SH, -SeH, and -TeH]. We observe an unprecedentedly large ∼650 meV red-shift in the lowest energy optical absorption band of (CdSe)₃₄ SCMs upon passivating their surface with Py-DTC ligands and the trend is found to be Ph- < Naph- < Anth- < Py-DTC. This shift is reversible upon removal of Py-DTC by triethylphosphine gold(i) chloride treatment at room temperature. Furthermore, we performed temperature-dependent (80-300 K) photoluminescence lifetime measurements, which show longer lifetime at lower temperature, suggesting a strong influence of hole wave function delocalization rather than carrier trapping and/or phonon-mediated relaxation. Taken together, knowledge of how ligands electronically interact with the SCM surface is crucial to semiconductor nanomaterial research in general because it allows the tuning of electronic properties of nanomaterials for better charge separation and enhanced charge transfer, which in turn will increase optoelectronic device and photocatalytic efficiencies.

One-Pot Synthesis of Nickel-Modified Carbon Nitride Layers Toward Efficient Photoelectrochemical Cells

A new method to significantly enhance the photoelectrochemical properties of phenyl-modified carbon nitride layers via the insertion of nickel ions into carbon nitride layers is reported. The nickel ions are embedded within the carbon nitride layers by manipulating the interaction of Ni ions and molten organic molecules at elevated temperature prior to their condensation. A detailed analysis of the chemical and photophysical properties suggests that the nickel ions dissolve in the molten molecules, leading to the homogeneous distribution of nickel atoms within the carbon nitride layers. We found that the nickel atoms can alter the growth mechanism of carbon nitride layers, resulting in extended light absorption, charge transfer properties, and the total photoelectrochemical performance. For the most photoactive electrode, the Ni ions have an oxidation state of 2.8, as confirmed by soft X-ray absorption spectroscopy. Furthermore, important parameters such as absorption coefficient, exciton lifetime, and diffusion length were studied in depth, providing substantial progress in our understanding of the photoelectrochemical properties of carbon nitride films. This work opens new opportunities for the growth of carbon nitride layers and similar materials on different surfaces and provides important progress in our understanding of the photophysical and photoelectrochemical properties of carbon nitride layers toward their implantation in photoelectronic and other devices.

Modifying Titania Using the Molten-Salt-Assisted Self-Assembly Process for Cadmium Selenide-Quantum Dot-Sensitized Photoanodes

Sensitizing titania with semiconducting quantum dots (QDs) is an important field for the development of third-generation photovoltaics. Many methods have been developed to effectively incorporate QDs over the surface of mesoporous titania, assembled from the 20-25 nm titania nanoparticles. Here, we introduce a molten-salt-assisted self-assembly (MASA) method to fabricate CdSe-modified mesoporous titania photoanodes. A mixture of ethanol, two surfactants (cetyltrimethylammonium bromide and 10-lauryl ether), silica (tetramethyl orthosilicate) or titania source (Ti(OC₄H₉)₄, acid (HNO₃), and cadmium nitrate solution was infiltrated into the pores of mesoporous titania (assembled using Degussa 25, P25) and immediately calcined at 450 °C to obtain mesoporous cadmium oxide-silica-titania (meso-CdO-SiO₂-P25) or cadmium titanate-titania (meso-CdTiO₃-P25) films. The MASA process is a simple method to smoothly coat or fill the pores of titania with mesoporous CdO-SiO₂ or CdTiO₃ that can be reacted under an H₂Se atmosphere to convert cadmium species to CdSe at 100 °C. Etching of the silica films with a very dilute hydrogen fluoride solution produces mesoporous CdSe-titania (meso-CdSe-P25) electrodes. The method is flexible to adjust the CdSe/TiO₂ mole ratio over a very broad range in the films. The films were characterized at every stage of the preparation to demonstrate the effectiveness of the method. The electrodes were also tested in a simple two-electrode solar cell to demonstrate the performance of the electrodes that have a power conversion efficiency of 3.35%.

An efficient charge separation and photocurrent generation in the carbon dot-zinc oxide nanoparticle composite

The development of light harvesting systems based on heterostructures for efficient conversion of solar energy to renewable energy is an emerging area of research. Here, we have designed heterostructures by using carbon dots (C-dots) and zinc oxide nanoparticles (ZnO NP) to develop an efficient light harvesting system. Interestingly, the conduction band and the valence band positions of ZnO NP are lower than the LUMO and HOMO positions of C-dots in this type II heterostructure of C dot-ZnO NP, which causes efficient charge separation and photocurrent generation. Steady state and time resolved spectroscopic studies reveal that an efficient photoinduced electron transfer occurs from C dots to ZnO NP and a simultaneous hole transfer occurs from the valence band of ZnO NP to the HOMO of C dots. The calculated rate of electron transfer is found to be 3.7 × 10⁹ s^-1 and the rate of hole transfer is found to be 3.6 × 10⁷ s^-1. The enhancement of photocurrent (11 fold) under solar light irradiation of the C dot-ZnO NP heterostructure opens up new possibilities to design efficient light harvesting systems.

Dual-Functional Surfactant-Templated Strategy for Synthesis of an In Situ N2 -Intercalated Mesoporous WO3 Photoanode for Efficient Visible-Light-Driven Water Oxidation

N₂ -Intercalated crystalline mesoporous tungsten trioxide (WO₃ ) was synthesized by a thermal decomposition technique with dodecylamine (DDA) as a surfactant template with a dual role as an N-atom source for N₂ intercalation, alongside its conventional structure-directing role (by micelle formation) to induce a mesoporous structure. N₂ physisorption analysis showed that the specific surface area (57.3 m²  g^-1 ) of WO₃ templated with DDA (WO₃ -DDA) is 2.3 times higher than that of 24.5 m²  g^-1 for WO₃ prepared without DDA (WO₃ -bulk), due to the mesoporous structure of WO₃ -DDA. The Raman and X-ray photoelectron spectra of WO₃ -DDA indicated intercalation of N₂ into the WO₃ lattice above 450 °C. The UV/Vis diffuse-reflectance spectra exhibited a significant shift of the absorption edge by 28 nm, from 459 nm (2.70 eV) to 487 nm (2.54 eV), due to N₂ intercalation. This could be explained by the bandgap narrowing of WO₃ -DDA by formation of a new intermediate N 2p orbital between the conduction and valance bands of WO₃ . A WO₃ -DDA-coated indium tin oxide (ITO) electrode calcined at 450 °C generated a photoanodic current under visible-light irradiation below 490 nm due to photoelectrochemical water oxidation, as opposed to below 470 nm for ITO/WO₃ -bulk. The incident photon-to-current conversion efficiency (IPCE=24.5 %) at 420 nm and 0.5 V versus Ag/AgCl was higher than that of 2.5 % for ITO/WO₃ -bulk by one order of magnitude due to N₂ intercalation and the mesoporous structure of WO₃ -DDA.

Alloying Strategy in Cu-In-Ga-Se Quantum Dots for High Efficiency Quantum Dot Sensitized Solar Cells

I-III-VI₂ group "green" quantum dots (QDs) are attracting increasing attention in photoelectronic conversion applications. Herein, on the basis of the "simultaneous nucleation and growth" approach, Cu-In-Ga-Se (CIGSe) QDs with light harvesting range of about 1000 nm were synthesized and used as sensitizer to construct quantum dot sensitized solar cells (QDSCs). Inductively coupled plasma atomic emission spectrometry (ICP-AES), wild-angle X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses demonstrate that the Ga element was alloyed in the Cu-In-Se (CISe) host. Ultraviolet photoelectron spectroscopy (UPS) and femtosecond (fs) resolution transient absorption (TA) measurement results indicate that the alloying strategy could optimize the electronic structure in the obtained CIGSe QD material, thus matching well with TiO₂ substrate and favoring the photogenerated electron extraction. Open circuit voltage decay (OCVD) and impedance spectroscopy (IS) tests indicate that the intrinsic recombination in CIGSe QDSCs was well suppressed relative to that in CISe QDSCs. As a result, CIGSe based QDSCs with use of titanium mesh supported mesoporous carbon counter electrode exhibited a champion efficiency of 11.49% (J_sc = 25.01 mA/cm², V_oc = 0.740 V, FF = 0.621) under the irradiation of full one sun in comparison with 9.46% for CISe QDSCs.

Core-shell PbS/Sn:In2O3 and branched PbIn2S4/Sn:In2O3 nanowires in quantum dot sensitized solar cells

Core-shell PbS/Sn:In₂O₃ and branched PbIn₂S₄/Sn:In₂O₃ nanowires have been obtained via the deposition of Pb over Sn:In₂O₃ nanowires and post growth processing under H₂S between 100 °C-200 °C and 300 °C-500 °C respectively. The PbS/Sn:In₂O₃ nanowires have diameters of 50-250 nm and consist of cubic PbS and In₂O₃ while the PbIn₂S₄/Sn:In₂O₃ nanowires consist of PbIn₂S₄ branches with diameters of 10-30 nm and an orthorhombic crystal structure. We discuss the growth mechanisms and also show that the density of electrons in the n-type Sn:In₂O₃ core is strongly dependent on the thickness of the p-type PbS shell, which must be smaller than 30 nm to prevent core depletion, via the self-consistent solution of the Poisson-Schrödinger equations in the effective mass approximation. The PbS/Sn:In₂O₃ and PbIn₂S₄/Sn:In₂O₃ nanowire networks had resistances of 100-200 Ω due to the large carrier densities and exhibited defect related photoluminescence at 2.2 eV and 1.5 eV respectively. We show that PbS in contact with polysulfide electrolyte has ohmic like behavior but the PbS/Sn:In₂O₃ nanowires gave, rectifying current voltage characteristics as a counter electrode in a quantum dot sensitized solar cell using a conventional ITO/TiO₂/CdS/CdSe photo anode, an open circuit voltage of ≈0.5 V, and short circuit current density of ≈1 mA cm^-2. In contrast the branched PbIn₂S₄/Sn:In₂O₃ nanowires exhibited a higher current carrying capability of ≈7 mA cm^-2 and higher power conversion efficiency of ≈2%.

Metal doped mesoporous FeOOH nanorods for high performance supercapacitors

In the present study, the effect of doping of foreign atoms on the parent atoms and the application of the resultant material for energy storage are successfully investigated.

Light-driven hydrogen production from aqueous solutions based on a new Dubois-type nickel catalyst

We developed a new water soluble CdSe/Ni hybrid, which yields remarkable photon-to-H₂ efficiency among all noble-metal free systems based on synthetic Ni molecular catalysts.

Roles of the methyl and methylene groups of mercapto acids in the photoluminescence efficiency and carrier trapping dynamics of CdTe QDs

Highly luminescent CdTe QDs capped by mercapto acids are developed and the influence of capping agents on luminescence and carrier trapping dynamics is studied.

Loss channels in triplet–triplet annihilation photon upconversion: importance of annihilator singlet and triplet surface shapes

Differences in triplet–triplet annihilation photon upconversion efficiencies between structurally similar annihilators can be understood in terms of singlet and triplet surface shapes.

A novel TiO2 nanostructure as photoanode for highly efficient CdSe quantum dot-sensitized solar cells

For sensitized solar cells, photoanodes combining the advantages of TiO₂ nanoparticles (high specific surface area) and one-dimensional (1D) nanostructures (fast transport channels) are ideal for obtaining highly efficient sensitized solar cells.

Improving Loading Amount and Performance of Quantum Dot-Sensitized Solar Cells through Metal Salt Solutions Treatment on Photoanode

Increasing QD loading amount on photoanode and suppressing charge recombination are prerequisite for high-efficiency quantum dot-sensitized solar cells (QDSCs). Herein, a facile technique for enhancing the loading amount of QDs on photoanode and therefore improving the photovoltaic performance of the resultant cell devices is developed by pipetting metal salt aqueous solutions on TiO₂ film electrode and then evaporating at elevated temperature. The effect of different metal salt solutions was investigated, and experimental results indicated that the isoelectric point (IEP) of metal ions influenced the loading amount of QDs and consequently the photovoltaic performance of the resultant cell devices. The influence of anions was also investigated, and the results indicated that anions of strong acid made no difference, while acetate anion hampered the performance of solar cells. Infrared spectroscopy confirmed the formation of oxyhydroxides, whose behavior was responsible for QD loading amount and thus solar cell performance. Suppressed charge recombination based on Mg²⁺ treatment under optimal conditions was confirmed by impedance spectroscopy as well as transient photovoltage decay measurement. Combined with high-QD loading amount and retarded charge recombination, the champion cell based on Mg²⁺ treatment exhibited an efficiency of 9.73% (J_sc = 27.28 mA/cm², V_oc = 0.609 V, FF = 0.585) under AM 1.5 G full 1 sun irradiation. The obtained efficiency was one of the best performances for liquid-junction QDSCs, which exhibited a 10% improvement over the untreated cells with the highest efficiency of 8.85%.