CdSe Photoanodes Research Articles

Enhanced Photoelectrochemical Performance by Constructing CdS/CdSe Heterojunction Structure

The growing need for sustainable energy development has become a critical issue due to worsening environmental pollution and climate change. Among the various technologies, the photoelectrochemical technology has been recognized as one of the essential approaches for advancing sustainable energy production. Out of the semiconductor materials used in PEC systems, cadmium sulfide (CdS) and cadmium selenide (CdSe) have been widely studied as promising candidates due to their advantageous properties. CdS, with a bandgap of 2.4 eV and high photoactivity, and CdSe, with a narrower bandgap of 1.9 eV and excellent light absorption characteristics, offer complementary advantages. In this study, we synthesized the CdS and CdSe materials via hydrothermal and chemical bath deposition methods, respectively, to fabricate a CdS/CdSe heterojunction photoanode system. The heterojunction CdS/CdSe photoanode formed a type-II structure, which facilitated efficient charge separation and transfer. Moreover, the CdS/CdSe photoanode exhibited high light absorption properties with very low charge transfer resistance, attributed to the role of CdS particles beneath CdSe as an electron transfer layer and the porous structure of the composite material. As a result, the CdS/CdSe photoanode achieved high photocurrent density of 4.51 mA·cm<sup>-2</sup> comparing to their individual cases, representing a 78% improvement in PEC performance compared to the only CdSe photoanode case.

Formation of a potential barrier by a ZnSXSe1−X electron-blocking layer to improve the efficiency of CdSe0.3S0.7/CdSe quantum dot sensitized solar cells

We designed and fabricated multilayer quantum dots sensitized solar cells (QDSCs) with TiO2 NPs/CdSe0.3S0.7/CdSe/ZnSXSe1−X, X = S/S + Se = 0, 0.7, 0.8, 0.9, and 1 photoelectrodes to achieve optimum power conversion efficiency (PCE). In the corresponding structure, incoming light is absorbed by the CdSe0.3S0.7 and CdSe quantum dots (QDs), while the ZnSXSe1−X QDs act as an electron blocking layer or passivation layer, forming an energy barrier that restricts electron mobility from the light absorbers to the polysulfide electrolyte. The beneficial effect of the alloyed ZnSXSe1−X layer is the adjustability of its nanoparticle size/bandgap energy proportional to variations in the concentration of anionic precursors X, according to optical results. The PCE value of the reference cell with the TiO2 NPs/CdSe0.3S0.7/CdSe photoanode is 4.15 %. Following the coating of ZnSe, ZnS0.7Se0.3, ZnS0.8Se0.2, ZnS0.9Se0.1, and ZnS QDs via two successive ionic layer adsorption and reaction (SILAR) cycles (2Sc) on the CdSe0.3S0.7/CdSe co-sensitized photoelectrode increasing stability and improving the PCE value to 4.9 %, 5.40 %, 5.70, 5.25 %, and 5.05 %, respectively. Next, by modifying the thickness of the champion cell's passivation layer, the QDSCs with TiO2 NPs/CdSe0.3S0.7/CdSe/ZnS0.8Se0.2 (3Sc) photoelectrode exhibit maximum photovoltaic performance parameters of short circuit current density (JSC) = 26.25 mA/cm2, open circuit voltage (VOC) = 560 mV, fill factor (FF) = 0.42 % and PCE = 6.15 %. This improvement in performance is the result of decreased internal energy loss and recombination of charge carriers at the interface between the electrolyte and photoelectrode, which increases electron collection efficiency and electron injection efficiency in the visible region according to the external and internal quantum efficiency curves.

Engineering the synthesized colloidal CuInS2 passivation layer in interface modification for CdS/CdSe quantum dot solar cells.

Interface modification is an important means to enhance the photovoltaic performance of quantum dot sensitized solar cells (QDSCs). The TiO2/CdS/CdSe solar cells are sensitized with CdS QDs and CdSe QDs, which inevitably introduces a new interface to form a recombination center. Therefore, it is necessary to coat a passivation layer in order to effectively inhibit charge recombination at the CdS/CdSe interface. In this work, CuInS2 (CIS) has been introduced into the CdS/CdSe QD system as an inner passivation layer and the CdS/CIS/CdSe photoanode structure has been fabricated in an environmentally friendly manner. The extracted charge amount (Q) is used to express the charge separation efficiency, indicating that we have obtained outstanding charge extraction efficiency in CIS based CdS/CdSe QDSCs. As a result, the photocurrent density of the TiO2/CdS/CIS/CdSe photoanode significantly has increased from 19.01 mA cm-2 to 22.74 mA cm-2 (TiO2/CdS/CdSe photoanode), which demonstrates a higher photoconversion efficiency of 4.52% in comparison with that of TiO2/CdS/CdSe photoanode.

Analysis of Stacked-Photo-Anode for Photoelectrochemical Water Splitting Reaction

In photoelectrochemical water splitting, every impinging photon should not only be absorbed but also be utilized towards reaction. While increasing photoelectrode thickness in photoelectrochemical reactors facilitates photon absorption, it has a debilitating effect on efficiency if the thickness required for complete photon absorption is much more than the exciton diffusion length, which is a property determined by the material and its processing. To address this issue, we demonstrate a general experimental methodology with a stack of CdSe photoanodes wherein the thickness of each photoelectrode is of the order of exciton diffusion length and which improves overall photocurrent by about 50%.

Fabrication of pyramid-BiVO4/CdSe composite with controlled surface oxygen vacancies boosting efficient carriers’ separation for photocathodic protection

• A novel pyramid-BiVO 4 /CdSe photoanode with enriched oxygen vacancies was prepared. • Pyramid-BiVO 4 /CdSe heterojunction promotes solar harvesting and carrier separation. • The pyramid-BiVO 4 /CdSe photoanode exhibits superior PEC performance and stability. • The corrosion potential of 304SS coupled with 8V-BC photoanode drop 708 mV. In order to solve the bottleneck problem of weak efficiency of carriers’ separation and transfer in BiVO 4 photocatalyst, a novel pyramid-BiVO 4 with sufficient oxygen vacancies was successfully synthesized via a low-temperature solvothermal method. By adjusting solution pH and adding SDBS surfactant, the prepared samples could have a variety of controllable morphologies and exposed {0 0 1} facets, which were determined by SEM, XRD, and BET methods. XPS O1s peak and ESR signals indicated that pyramid-BiVO 4 exhibited higher oxygen vacancies concentration than others. Besides, CdSe quantum dots (QDs) were introduced to construct BiVO 4 /CdSe heterojunctions composite based photoanode to further promote solar harvesting and carrier separation. The photoelectrochemical experimental results showed that 304 stainless steel (304SS) coupled with 8V-BC photoanode showed an enhanced photocurrent density (608 μA·cm −2 ) and maximum potential drop (708 mV), which were equivalent to 5.06 times and 2.10 times that of the original BiVO 4 , respectively. Mechanism study illustrated that the ultra-high performance of the 8V-BC photoanode was attributed to the synergistic effect of enriched oxygen vacancies, exposed {0 0 1} facets, enlarged visible light absorption and larger specific surface area.

Effect of Organic Additives on Properties of Electrodeposited CdSe Photoanodes

Thin CdSe films were produced by electrodeposition at a constant potential onto glass/FTO conducting substrates from sulfuric acid electrolytes (pH 2.2) containing cadmium sulfate, sodium selenite, and addition of sodium lignosulfonates as a surfactant. The films were characterized by X-ray diffraction analysis, Raman spectroscopy, scanning electron microscopy, atomic-force microscopy, spectrophotometry, and photoelectrochemical measurements to examine their structure, composition, surface morphology, and electrical and optical properties. It was found that sodium lignosulfonate improves the electrical properties of the electrodeposited CdSe photoanodes. The operation of a CdSe/FTO/glass photoanode was tested in an electrochemical cell with electrolyte containing the Fe2+/3+ redox pair with various illumination sources.

Accumulation of Solar Hydrogen in the Photoelectrochemical System Based on CdSe Photoanode and MH Cathode

The film photoanodes based on CdSe and NT-TiO2/CdSe have been formed by the electrochemical and painting methods. It is shown that the introduction of graphene oxide into the structure of the semiconductor CdSe film promotes absorption of light and leads to improvement in their characteristics by 25-30 %. The compatibility of the cathode based on composite of hydrogen-sorbing intermetallic alloys LaNi4.5Mn0.5 + LaNi3.5Al0.7Mn0.8 with current-conductive additives in pair with the CdSe photoanode is shown. It was found that 95 – 98 % of the total current generated under the influence of sunlight at the anodes was used on the formation and accumulation of hydrogen by cathodes.

PREPARED QUANTUM DOTS SENSITIZED SOLAR CELLS BASED ON TiO2/CdS:Mn2+/CdSe PHOTOANODE

In this study, we have prepared and investigated the optical properties of the TiO2/CdS:Mn2+/CdSe photoanode as the function of Mn2+ doping concentration and thickness. The results show that the peaks of the UV-Vis spectra shifted toward longer wavelength while Mn2+ doping concentrations or thickness of the films were changed. The main cause of the red-shifting in UV-Vis spectra may come from the increasing of photoanode light-harvesting capacity. In addition, the results also demonstrated by the boosting performance of quantum dots sensitized solar cells from 2.07% for TiO2/CdS/CdSe photoanode to 2.5% for TiO2/CdS:Mn2+/CdSe photoanode.

The photoelectrochemical cell with hydrogen accumulation at the conditions of natural insolation

The film photoanodes based on CdSe and NT-TiO2/CdSe have been formed by the electrochemical and painting methods. It is shown that the introduction of graphene oxide into the structure of the semiconductor CdSe film promotes absorption of light and leads to improvement in their characteristics by 25-30 %. The compatibility of the cathode based on composite of hydrogen-sorbing intermetallic alloys LaNi4.5Mn0.5 + LaNi3.5Al0.7Mn0.8 with current-conductive additives in pair with the CdSe photoanode is shown. It was found that 95 – 98 % of the total current generated under the influence of sunlight at the anodes was used on the formation and accumulation of hydrogen by cathodes.

High current density cation-exchanged SnO2–CdSe/ZnSe and SnO2–CdSe/SnSe quantum-dot photoelectrochemical cells

The 9.74 mA cm−2current density of SnO2–CdSe photoanode is enhanced to 19.82 and 28.40 mA cm−2on SnO2–CdSe/ZnSe and SnO2–CdSe/SnSe surface modifications, respectively, through a process of cation-exchange.

Distinctly Improved Photocurrent and Stability in TiO2 Nanotube Arrays by Ladder Band Structure

Introducing a ternary interlayer into binary heterostructures to construct a ladder band structure provides a promising way for photoelectrochemical water splitting. Here, we design and fabricate a sandwich structure on TiO2 nanotubes using CdSxSe1–x as the interlayer to obtain a matching band alignment. The photoelectrochemical (PEC) properties of composite photoanodes are optimized by the order of sensitization and elements ratio, wherein the TiO2/CdS/CdS0.5Se0.5/CdSe photoanode shows a significantly enhanced photocurrent of 14.78 mA cm–2 at −0.2 V vs SCE, exhibiting a nearly 15-fold enhancement, over 1 order of magnitude. The quantum efficiency apparently increases to 40% at a range of 400–520 nm, resulting from the fact that a sensitizing layer with a matching band alignment can facilitate the separation of photogenerated electron–hole pairs and also extend the absorption range to the visible region due to its narrow bandgaps. Furthermore, its stability was distinctly improved by coating MoS2 on the s...

Improved photovoltaic performance of quantum dot-sensitized solar cells using multi-layered semiconductors with the effect of a ZnSe passivation layer

ZnSe was deposited on a TiO2/PbS/CdS/CdSe photoanode, which was more efficient in reducing electron recombination in the QDSSCs.

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%.

Synthesis and studies on effect of indium doping on physical properties of electrodeposited CdSe thin films

Semiconducting CdSe and indium doped CdSe (In: CdSe) thin films have been synthesized on stainless steel and fluorine doped tin oxide coated glass substrates in an aqueous medium using a potentiostatic mode of electrodeposition. The doping concentration of indium has been optimized to 0.15 vol% using the reliable photoelectrochemical technique. To study the effect of indium doping these films are characterized using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping, Raman spectroscopy, contact angle measurement and UV–visible spectrophotometry techniques. CdSe and In: CdSe thin films are low crystalline with a cubic crystal structure. The valence states of CdSe and In: CdSe thin films are analyzed by means of XPS. Undoped CdSe thin film shows fiberlike morphology, which transforms into a beautiful web of nanofibers upon doping. The Elemental composition of both films analyzed by means of energy dispersive X-ray spectroscopy. Raman studies show transverse optical and longitudinal optical modes of phonon. Indium doping improves the hydrophilic nature of CdSe photoanode. The optical band gap (direct) found to be decreased from 2.02 to 1.67 eV upon indium doping. Both films are photoactive in nature.

Influence of Mn+2 incorporation in CdSe quantum dots for high performance of CdS–CdSe quantum dot sensitized solar cells

Quantum dot sensitized solar cells (QDSSCs) have attracted considerable attention recently and become promising candidates for realizing a cost-effective and facile fabrication of solar cell with improved photovoltaic performance. QDs were directly grown on the TiO2 mesostructure by the successive ionic layer absorption and reaction (SILAR) technique. QDSSC based on CdS–CdSe photoanode achieves a power conversion efficiency of 3.42% under AM 1.5 G one sun illumination. The loading of Mn+2 metal ions was applied to a CdSe (CdS–Mn–CdSe) photoanode to enhance the absorption in QDSSCs, which greatly improved the power conversion efficiency. Without the passivation layer, the solar cell based on a CdS–Mn–CdSe QD-sensitized TiO2 photoelectrode shows higher Jsc (14.67 mA/cm2), Voc (0.590 V) and power conversion efficiency (4.42%) comparing to Mn-undoped CdS–CdSe QD sensitized TiO2 (Jsc: 11.29 mA/cm2, Voc: 0.568 V, and efficiency: 3.42%), which can be ascribed to superior light absorption, faster electron transport and slower charge recombination for the former. The effective electron lifetime of the device with CdS–Mn–CdSe was higher than those with CdS–CdSe, leading to more efficient electron–hole separation and slower electron recombination. The effects of Mn+2 metal ions on the chemical, physical, and photovoltaic properties of the QDSSCs have been investigated have been investigated by X-ray photon spectroscopy (XPS), UV–vis spectra, photocurrent–voltage (J–V) characteristics and electrochemical impedance spectra (EIS).

Thiocyanate functionalized ionic liquid electrolyte for photoelectrochemical study of cadmium selenide pebbles

A thiocyanate functionalized ionic liquid based electrolyte is developed for the application in CdSe thin film solar cell. An aqueous solvent consisting of polysulfide and thiocyanate functionalized IL has been found as the optimum solvent for preparing the liquid electrolytes. This solvent ratio appears to give higher cell efficiency compared to pure aqueous polysulfide electrolyte. Polysulfide and thiocyanate functionalized IL give rise to a good redox couple in the electrolyte for photoelectrochemical performance. The CdSe photoanode used for solar cell study has been synthesized by a simple and cost-effective one-step, one-pot chemical bath deposition method onto the F: SnO2 substrates. The as-deposited films were annealed at temperatures 100, 200, 300 and 400°C, respectively for 1h in ambient air. The maximum current density of 3.55mA/cm2 for the sample annealed at 300°C is observed in the polysulfide electrolyte with the power conversion efficiency 0.76%. Addition of thiocyanate functionalized IL in polysulfide produced the highest current density of 4.93mA/cm2 with the two fold increase in the power conversion efficiency up to 1.32%.

Comparative Study of Tungsten Monocarbide and Platinum as Counter Electrodes in Polysulfide-Based Photoelectrochemical Solar Cells

The stability and the electrocatalytic activity of polycrystalline tungsten monocarbide (WC) and platinum (Pt) electrodes in a concentrated polysulfide electrolyte were examined in an electrochemical half-cell and an integrated photoelectrochemical cell (PEC) device. Cyclic voltammetry and linear sweep voltammetry measurements found WC electrodes to be approximately twice as active as Pt electrodes toward polysulfide reduction. Electrochemical and X-ray photoelectron spectroscopy (XPS) measurements indicated that WC was stable in a polysulfide electrolyte, with no appreciable W sulfide formation. In contrast, XPS showed significant levels of sulfide species on the Pt surface, which might explain the differences in the electrochemical behavior of the two electrode materials. The performance of integrated PEC devices comprised of thin-film CdSe photoanodes and WC or Pt counter electrodes in a polysulfide electrolyte was consistent with that predicted from electrochemical half-cell measurements.

Photocorrosion of Coupled CdS/CdSe Photoelectrodes Coated with ZnO: Atomic Force Microscopy and X‐Ray Diffraction Studies

The stability of photoelectrochemical cells based on chemically deposited CdS/CdSe coupled films has been examined. Changes in surface structure and composition of coated and uncoated coupled films as well as CdSe films have been examined by atomic force microscopy and X‐ray diffraction. The superior stability at short times of the coupled system, compared to CdSe, is related to the increase in the hexagonal character (stronger bonding) and the smaller recombination rate of the photogenerated carriers. At large operation times, the lower stability of the coupled system is related to band opening, which increases the oxidation rates of the passivating Se/S layer. The recrystallization illuminated CdSe photoanodes, and coupled films working in the dark can be explained by the presence of surface states and back reactions. Stable short‐circuit currents were obtained with coupled films coated with a thin layer (350 Å) of ZnO. It is likely that oxidation and redeposition of the protective ZnO film competes for hole consumption. The rough morphology of the coated photoelectrodes correlates to a substantial increase in surface area that resembles ZnO particulate film electrodes sensitized by CdSe and CdS.

Influence of surface treatments on CdSe thin films in photoelectro-chemical solar energy conversion

Photovoltaic performance of semiconductor-liquid junction solar cell using electro-codeposited thin filmn-CdSe is found to improve significantly by proper surface treatments. The solid state parameters of annealed films are calculated and compared with those of unannealed film-based cells. Chemical etching is found to improve short circuit current and fill factor whereas photoelectrochemical etching technique improves the stability of photoanode in polysulphide electrolyte. Annealing promotes incipient fusion of small crystallites, thus reducing the grain boundaries which are known to act as recombination centres for minority carriers and trapping centre for majority carriers. The conversion efficiency and stability are found to improve by chemical etching of the semiconductor layer because chemical etching pins Fermi level of CdSe photoanode and promotes exchange current density.

Photoelectrochemical oxidation of water at CdS and CdSe anodes coated with composites of conducting polymer containing RuO 2

CdS and CdSe single-crystal electrodes were modified by coating with composites of electrically conducting poly(bithiophene)-poly(pyrrole) copolymer and hydrophobia poly(vinyl chloride) (PVC), in combination with catalytic dispersion of RuO 2. These modifications were used in order to stabilize the semiconductor photoanodes during visible light-induced oxidation of water to oxygen. Simultaneous detection of evolved oxygen and dissolved cadmium ions shows a stabilization (i.e. fraction of the total photocurrent producing oxygen) of 85% for both CdS and CdSe. Adhesiveness, and hence stabilization efficiency, is enhanced by pre-coating the semiconductor with poly(bithiophene). The power efficiency of the self-driven CdS-based photoelectrolysis cell under 50 mV/cm 2 tungsten-halogen light is 0.42%. CdSe-based cells require the help of an external power source in order to achieve water cleavage. The efficiency of the photoassisted CdSe photoanode was estimated to 0.98%. Low efficiencies are explained by the high optical absorption of the protecting film, the transmittance of which is only 6%.