CdS Quantum Dot-sensitized Solar Cells Research Articles

Graphene/zinc aluminum mixed metal oxides photo anode for CdS quantum dot-sensitized solar cell

In this study, graphene was used to enhance the photovoltaic performance of the CdS quantum dot-sensitized solar cells (QDSSCs). The zinc aluminum mixed metal oxides (MMO) obtained from layered double hydroxide (LDH) precursor and the graphene/MMO hybrid materials were used as photoanode of the CdS QDSSCs, respectively. Raman spectroscopy, x-ray diffraction (XRD) and energy-dispersive x-ray spectroscopy (EDS) confirmed the existence of graphene in the photoanodes. The incorporated graphene influenced the specific areas and improved the light harvesting, thus increasing the photogenerated electrons. The addition of graphene improves the power conversion efficiency (PCE) of the QDSSCs, and the highest PCE of the QDSSCs with graphene/Zn–Al MMO photoanode reached 0.18%. Electrochemical impedance measurements indicated that graphene helped to increase the electron transfer rate in the graphene/Zn–Al MMO photoanode and reduce the charge recombination rate. This work highlights that graphene can act as a fast pathway for photogenerated electrons.

Preparation and photovoltaic properties of CdS quantum dot-sensitized solar cell based on zinc tin mixed metal oxides

The present study reports a new type of quantum dot sensitized solar cells (QDSSCs) using the zinc tin mixed metal oxides (MMO) as the anode materials, which were obtained from the layered double hydroxide (LDH) precursor. The successive ionic layer adsorption and reaction (SILAR) method is applied to deposit CdS quantum dots. The effects of sensitizing cycles on the performance of CdS QDSSC are studied. Scanning electron microscopy (SEM), Transmission electron microscope (TEM) and X-ray diffraction (XRD) are used to identify the surface profile and crystal structure of the mixed metal oxides anode. The photovoltaic performance of the QDSSC is studied by the electrochemical method. The new CdS QDSSC exhibits power conversion efficiency (PCE) up to 0.48% when the anode was sensitized for eight cycles.

Improving the stability of CdS quantum dot sensitized solar cell using highly efficient and porous CuS counter electrode

Thin films from copper sulfide (CuxS) are the most commonly used electrocatalyst counter electrodes (CEs) for high-efficiency quantum dot sensitized solar cells (QDSSCs) because of its superior electrocatalytic activity in the presence of polysulfide electrolytes. In addition to the stability issues, the CuxS CEs are usually prepared by complicated, costly, time consuming, and less productive methods, which are inadequate for practical applications of QDSSCs. In this work, we present a simple approach for fabricating an efficient and stable CE for QDSSCs using pure covellite phase CuS nanoparticles (NPs) pre-prepared via a cheap, fast, and scalable chemical method. The catalyst ink was obtained by mixing the as-prepared CuS NPs with polyvinylidene fluoride, as a polymeric binder, which was then directly applied to a conductive fluorine-doped tin oxide substrate without any further high temperature post treatment. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements were used to investigate the electrocatalytic activity of the CuS NPs CE. The power conversion efficiency of 2.6% was achieved from CdS QDSSC assembled with CuS NPs CE, which was higher than 1.57% for conventional Cu2S/brass and 1.33% for Pt CEs under one-sun illumination. The CdS QDSSC with CuS NPs CE was also able to supply a constant photocurrent value without any obvious decrease under light soaking test, in contrast to the devices with Cu2S/brass and Pt CEs, which showed inferior stability. This remarkable photovoltaic performance was attributed to the nanoporous morphology and the excellent electrocatalytic activity of CuS NPs CE.

ZnS shell-like CdS quantum dot-sensitized solar cell grown by SILAR approach; effect of electrolyte, counter electrode, and shell thickness

Quantum Dot (QD) sensitized solar cells due to their high potential have attracted tremendous attention to become a low cost and reliable substitute for the fossil fuels. This study reports fabrication and optimization of the CdS QDs sensitized cells connected to ZnO nanowires (NWs) which were grown by hydrothermal method. Optimization process was done using a set of experiments, which were designed to systematically extract the best values. ZnS shell-like CdS QDs were synthesized on the surface of ZnO NWs by successive ionic layer adsorption and reaction approach. The effect of the different components on the charge transfer was studied. The cell with ZnO NW/CdS(4C)/ZnS(3C) as the photosensitizer, CuS as the counter electrode and Na2S 0.6 M, S 0.2 M and KCl 0.4 M in methanol/water (7:3) as the electrolyte exhibited the best performance with the efficiency of 0.419%. Although increasing the dot thickness was supposed to improve the cell performance, defects occurred during the growth, due to large mismatch of core and the shell, decay the cell's efficiency.

Optimizing photovoltaic performance in CuInS2 and CdS quantum dot-sensitized solar cells by using an agar-based gel polymer electrolyte

Quantum dot-sensitized solar cells (QDSSCs) offer new opportunities to address the clean energy challenge, being one of the top candidates for third generation photovoltaics.

Enhancing Performance of CdS Quantum Dot-Sensitized Solar Cells by Two-Dimensional g-C3N4 Modified TiO2 Nanorods.

In present work, two-dimensional g-C3N4 was used to modify TiO2 nanorod array photoanodes for CdS quantum dot-sensitized solar cells (QDSSCs), and the improved cell performances were reported. Single crystal TiO2 nanorods are prepared by hydrothermal method on transparent conductive glass and spin-coated with g-C3N4. CdS quantum dots were deposited on the g-C3N4 modified TiO2 photoanodes via successive ionic layer adsorption and reaction method. Compared with pure TiO2 nanorod array photoanodes, the g-C3N4 modified photoanodes showed an obvious improvement in cell performances, and a champion efficiency of 2.31 % with open circuit voltage of 0.66 V, short circuit current density of 7.13 mA/cm2, and fill factor (FF) of 0.49 was achieved, giving 23 % enhancement in cell efficiency. The improved performances were due to the matching conduction bands and valence bands of g-C3N4 and TiO2, which greatly enhanced the separation and transfer of the photogenerated electrons and holes and effectively suppressed interfacial recombination. Present work provides a new direction for improving performance of QDSSCs.

One-step fabrication of copper sulfide nanoparticles decorated on graphene sheets as highly stable and efficient counter electrode for CdS-sensitized solar cells

Quantum-dot-sensitized solar cells (QDSSCs) are thin-film photovoltaics and highly promising as next-generation solar cells owing to their high theoretical efficiency, easy fabrication process, and low production cost. However, the practical photoconversion efficiencies (PCEs) of QDSSCs are still far below the theoretically estimated value owing to the lack of an applicable design of the materials and electrodes. In this work, we developed a highly stable and efficient counter electrode (CE) from copper sulfide nanocrystals and reduced graphene oxide (CuxS@RGO) for QDSSC applications. The CuxS@RGO electrocatalyst was successfully prepared by a facile one-pot hydrothermal method, then directly applied to a fluorine-doped tin oxide (FTO)-coated glass substrate by the simple drop-casting technique. Owing to the synergistic effect between CuxS nanocrystals and conductive RGO sheets, the CuxS@RGO CE showed high electrocatalytic activity for polysulfide electrolyte reduction. A CdS QDSSC based on the CuxS@RGO CE yielded a high and reproducible PCE of 2.36%, exceeding those of 1.57 and 1.33% obtained with the commonly used Cu2S/brass and Pt CEs, respectively. Moreover, the QDSSC with the CuxS@RGO CE showed excellent photostability in a light-soaking test without any obvious decay in the photocurrent, whereas the cell based on the Cu2S/brass CE was severely degraded.

The promising photo anode of graphene/zinc titanium mixed metal oxides for the CdS quantum dot-sensitized solar cell

In this study, the graphene sheets produced by supercritical CO2 exfoliation of graphite were used to improve the photovoltaic performance of the CdS quantum dot-sensitized solar cells (QDSSCs). The zinc titanium mixed metal oxides (MMO) based on layered double hydroxide (LDH) precursor and the graphene/MMO hybrid materials were used as photoanodes of the CdS QDSSCs, respectively. The presence of graphene in the photoanodes was confirmed by Raman spectroscopy, X-ray diffraction (XRD) and Energy-dispersive X-ray spectroscopy (EDS). The influence of graphene concentration on the performance of CdS QDSSCs was studied by electrochemical method. The addition of graphene enhanced QDs adsorption properties and lowered internal resistance, so the QDSSCs displayed higher power conversion efficiency (PCE). Accordingly, the highest PCE of the QDSSCs based on graphene/Zn-Ti MMO photoanode reached 0.44% and increased 37.5% in compared with that based on plain Zn-Ti MMO working electrodes.

Multiworking Electrode Flexible Fiber-Type Quantum Dot-Sensitized Solar Cells

Flexible fiber-type CdS quantum dot-sensitized solar cells (CdS FF-QDSSCs), in which all the components are assembled into a flexible plastic capillary tube, are designed and fabricated. In each FF-QDSSC, a Pt wire along the capillary tube axis acts as the counter electrode. A number of surrounding Ti wires coated with CdS-sensitized ZnO nanorods act as the working electrodes. This design provides the cells with good flexibility and all-direction light harvesting capability. The photovoltaic performances of the FF-QDSSCs can be effectively improved by increasing the number of the working electrodes up to six. The conversion efficiency of the cell with six working electrodes (FF-QDSSC-6) is more than five times that of the cell with only one working electrode. Furthermore, for simultaneously illuminating the cell from all the directions perpendicular to the capillary tube, an Al reflector is placed behind the cell. This measure raised the maximum power output of an FF-QDSSC-6 by 55%.

A novel PbS/TiO2 composite counter electrode for CdS quantum dot-sensitized ZnO nanorods solar cells

A series of novel PbS/TiO2 nanotubes was fabricated as counter electrodes (CEs) through a combination of anodic oxidation and successive ionic-layer adsorption and reaction methods. The photovoltaic-conversion efficiency of ZnO nanorods sensitized with CdS quantum dots using the optimized PbS(6)/TiO2 CE increased by nearly 440.8% and 227.5% compared with the efficiency of nanorods using planar Pt and bare TiO2 CE, respectively. Thus, the novel PbS/TiO2 composite CE was a promising catalytic electrode with excellent electrocatalytic activity for the reduction of charge carriers in polysulfide electrolyte.

Investigation of the role of Mn dopant in CdS quantum dot sensitized solar cell

Mn-doping into CdS quantum dots (QDs) has been demonstrated a useful way to enhance the power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs), the detailed systematic study is needed to get a better fundamental understanding. This work focuses on the study of the effects of Mn dopant on light harvesting, charge transfer, and charge collection of the solar cells. The results indicate that the Mn-doping into CdS QDs increases the light absorbance and extends the light absorption range, which results in the enhancement of the photo-generated current density. In addition, both the electron transport rate and the electron diffusion length are also increased with the introduction of Mn dopant. So the charge collection efficiency (ηcc) of the solar cell increases from 89.9% for CdS sample to 96.7% for Mn/CdS sample. As a result, the PCE of Mn/CdS QDSC reaches 3.29%, which is much higher than that of CdS QDSC (2.01%).

Employing 4-methoxybenzoic acid interfacial-modification to enhance the photovoltaic performance of CdS quantum dot-sensitized solar cells

The effect of incorporating self-assembled monolayers of 4-methoxybenzoic acid (MBA) on CdS quantum dot-sensitized (QDSSC) solar cells based on ZnO nanorods was evaluated. The MBA was deposited on the ZnO photoanode, with the deposition time being a process variable. Photoluminescence spectra indicated that the MBA modification can suppress the photogenerated electron–hole recombination processes and presumably passivate the surface defects. The ultraviolet photoemission spectroscopy results prove that MBA forms an energy barrier at the interface of ZnO and CdS which may retard the back transfer of electrons. Overall the inclusion of MBA imparts a weak positive enhancement of the photovoltaic performance of these QDSSCs and this is an approach that may be developed to give stronger effects using alternative chemistries.

ZnO Hierarchical Nanostructure Photoanode in a CdS Quantum Dot-Sensitized Solar Cell.

A hierarchical array of ZnO nanocones covered with ZnO nanospikes was hydrothermally fabricated and employed as the photoanode in a CdS quantum dot-sensitized solar cell (QDSSC). This QDSSC outperformed the QDSSC based on a simple ZnO nanocone photoanode in all the four principal photovoltaic parameters. Using the hierarchical photoanode dramatically increased the short circuit current density and also slightly raised the open circuit voltage and the fill factor. As a result, the conversion efficiency of the QDSSC based on the hierarchical photoanode was more than twice that of the QDSSC based on the simple ZnO nanocone photoanode. This improvement is attributable to both the enlarged specific area of the photoanode and the reduction in the recombination of the photoexcited electrons.

Enhanced performance of branched TiO2 nanorod based Mn-doped CdS and Mn-doped CdSe quantum dot-sensitized solar cell

TiO2 branched nanostructures could be efficient as photoanodes for quantum dot-sensitized solar cells (QDSCs) due to their large surface area for QD deposition. In this study, Mn-doped CdS/Mn-doped CdSe deposited branched TiO2 nanorods were fabricated to enhance the photovoltaic performance of QDSCs. Mn doping in CdS and CdSe retards the recombination losses of electrons, while branched TiO2 nanorods facilitate effective electron transport and compensate for the low surface area of the nanorod structure. As a result, the charge-transfer resistance (RCT), electron lifetime (τe), and the amount of QD deposition were significantly improved with branched TiO2 nanorod based Mn-doped CdS/Mn-doped CdSe quantum dot-sensitized solar cell.

Decrease of back recombination rate in CdS quantum dots sensitized solar cells using reduced graphene oxide**Project supported by the Fund from Taif University, Saudi Arabia (Grant No. 1/435/3524).

The photovoltaic performance of CdS quantum dots sensitized solar cells (QDSSCs) using the 0.2 wt% of reduced graphene oxide and TiO2 nanoparticles (RGO+TiO2 nanocomposite) photoanode is investigated. CdS QDs are adsorbed onto RGO+TiO2 nanocomposite films by the successive ionic layer adsorption and reaction (SILAR) technique for several cycles. The current density–voltage (J–V) characteristic curves of the assembled QDSSCs are measured at AM1.5 simulated sunlight. The optimal photovoltaic performance for CdS QDSSC was achieved for six SILAR cycles. Solar cells based on the RGO+TiO2 nanocomposite photoanode achieve a 33% increase in conversion efficiency (η) compared with those based on plain TiO2 nanoparticle (NP) photoanodes. The electron back recombination rates decrease significantly for CdS QDSSCs based on RGO+TiO2 nanocomposite photoanodes. The lifetime constant (τ) for CdS QDSSC based on the RGO+TiO2 nanocomposite photoanode is at least one order of magnitude larger than that based on the bare TiO2 NPs photoanode.

Effect of the nature of cationic precursors for SILAR deposition on the performance of CdS and PbS/CdS quantum dot-sensitized solar cells

In this work, the influences of cationic precursors on the quality of photoelectrode, consequently on the performance of the quantum dot-sensitized solar cells (QDSCs) have been studied. CdS QDSCs have been prepared using successive ionic layer absorption and reaction (SILAR) method. Three cadmium precursors including nitrate (Cd(NO3)2), chloride (CdCl2), and acetate (Cd(Ac)2) were employed for the synthesis and absorption of CdS nanoparticles on nanostructure TiO2 film. The loading amount and nanoparticle size of the CdS on mesoporous TiO2 film showed a significant difference while using various cadmium precursors in the same SILAR cycles. Both the light-harvesting ability and the obtained incident photon-to-current conversion efficiency values show the trend of deposition rate caused by cadmium precursors. Further, it was proposed that an effective cationic precursor could provide a good connection between QD sensitizer and TiO2 interface by electrochemical impedance spectroscopy analysis. Under AM 1.5 G full one sun illumination, the final power conversion efficiency of CdS QDSC based on Cd(Ac)2 was 2.10 %, and PCE values of 1.57 and 1.20 % were obtained for solar cells sensitized by CdS QDs prepared by CdCl2 and Cd(NO3)2, respectively. The cationic precursor effect was further applied in PbS/CdS co-sensitized solar cells. The PbS/CdS QDSCs based on acetate cationic precursors provide a photocurrent of 19.24 mA/cm2 and PCE of 3.23 % in comparison with 11.26 mA and 2.13 % obtained with nitrate acetate salts. Noticeably, the CdS and PbS/CdS QDSCs based on various cationic precursors prepared by SILAR exhibited good photocurrent stability under several light on–off cycles.

The photovoltaic performance of CdS quantum dots sensitized solar cell using graphene/TiO2 working electrode

Graphene/titania (G/TiO2) nanocomposite photoanodes were fabricated for CdS quantum dots sensitized solar cells (QDSSCs) applications. The effect of G/TiO2 ratio (0, 0.1, 0.2, 0.5, and 1.0wt.%) on the photovoltaic performance of CdS QDSSCs was investigated. CdS QDs were deposited onto G/TiO2 nanocomposite films by successive ionic layer adsorption and reaction (SILAR) technique for six cycles. The current density–voltage (J–V) characteristic curves of the assembled solar cells were measured at AM1.5 simulated sunlight. The optimal G/TiO2 ratio was 0.2wt.% for photovoltaic performance. CdS QDSSCs based on 0.2wt.% G/TiO2 nanocomposite photoanode achieve 32% increase in conversion efficiency (η) compared with those based on plain TiO2 NPs photoanode. The photovoltage–decay curves of the assembled cell were recorded. The electron–hole back recombination rates decrease significantly for CdS QDSSCs based on 0.2wt.% ratio of G/TiO2 nanocomposite photoanode. The lifetime constants (τ) is much larger for CdS QDSSCs based on 0.2wt.% ratio of G/TiO2 nanocomposite photoanode compared to those based on plain TiO2 NPs photoanodes.

Morphology of the Electrospun TiO2 on the Photovoltaic Properties of CdS Quantum Dot-Sensitized Solar Cells.

Various TiO2 building blocks i.e., spheres (S-TiO2), rods (R-TiO2) grains (G-TiO2) were produced by electrospinning technique and sensitized by CdS via successive ionic layer adsorption and reaction (SILAR) to investigate their morphological effect on the photovoltaic properties of quantum dot-sensitized solar cells (QDSCs). It was found that QDSCs with G-TiO2 achieved the highest overall conversion efficiency of 1.74% under one-sun AM1.5G illumination, which corresponds to an increase of -100% (0.87%) compared with S-TiO2 and -35% (1.29%) with R-TiO2, respectively. Electrochemical impedance spectroscopy shows a largest recombination resistance for G-TiO2 cells amongst the three which accounts for its superior photovoltaic performance.

A strategy to improve the energy conversion efficiency and stability of quantum dot-sensitized solar cells using manganese-doped cadmium sulfide quantum dots.

This article describes the effect of manganese (Mn) doping in CdS to improve the photovoltaic performance of quantum dot sensitized solar cells (QDSSCs). The performances of the QDSSCs are examined in detail using a polysulfide electrolyte with a copper sulfide (CuS) counter electrode. Under the illumination of one sun (AM 1.5 G, 100 mW cm(-2)), 10 molar% Mn-doped CdS QDSSCs exhibit a power conversion efficiency (η) of 2.85%, which is higher than the value of 2.11% obtained with bare CdS. The improved photovoltaic performance is due to the impurities from Mn(2+) doping of CdS, which have an impact on the structure of the host material and decrease the surface roughness. The surface roughness and morphology of Mn-doped CdS nanoparticles can be characterised from atomic force microscopy images. Furthermore, the cell device based on the Mn-CdS electrode shows superior stability in the sulfide/polysulfide electrolyte in a working state for over 10 h, resulting in a highly reproducible performance, which is a serious challenge for the Mn-doped solar cell. Our finding provides an effective method for the fabrication of Mn-doped CdS QDs, which can pave the way to further improve the efficiency of future QDSSCs.

A bifacial quantum dot-sensitized solar cell with all–cadmium sulfide photoanode

Pursuit of a high power conversion efficiency and reduction of electricity-generation cost has been a persistent objective for quantum dot-sensitized solar cells (QDSSCs). We present here the fabrication of a QDSSC comprising a nanoflower-structured CdS anode, a liquid electrolyte having S2−/Sn2− redox couples, and a transparent CoSe counter electrode. Nanoflower-structured CdS anodes are prepared by a successive ionic layer adsorption and reaction (SILAR) method and subsequently hydrothermal strategy free of any surfactant or template. The CdS nanoparticles synthesized by a SILAR method act as “seed crystal” for growth of CdS nanoflowers. The average electron lifetime is markedly elevated in nanoflower-structured CdS anode in comparison with CdS nanoparticle or nanoporous CdS microsphere anode. Herein, we study the effect of synthesis method on CdS morphology and solar cell's photovoltaic performance, showing a power conversion efficiency of 1.67% and 1.17% for nanoflower-structured CdS QDSSC under front and rear irradiations, respectively.