CdS Quantum Dot-sensitized Solar Cells Research Articles

Synthesis, characterization and electrochemical impedance study of CdS quantum dot-sensitized solar cell with reduced graphene oxide/TiO2 composite photoanode

Synthesis, characterization and electrochemical impedance study of CdS quantum dot-sensitized solar cell with reduced graphene oxide/TiO2 composite photoanode

Efficient triple-layer photoanode incorporated with nitrogen-doped TiO<sub>2</sub> nanocrystals for CdS quantum dot-sensitized solar cells

The Ceylon Journal of Science is a peer-reviewed journal published quarterly by the University of Peradeniya, Sri Lanka in March, June, September and December. It is aimed at publishing high quality research articles on topics related to different disciplines in Science. The journal accepts original research articles, book reviews, reviews and mini-reviews, short communications, opinions, research notes, and commentaries and notes. The Journal has its own website https://site.pdn.ac.lk/cjs/. The journal strictly adheres to publication ethics as emphasized by the Committee on Publication Ethics (COPE). It is indexed in Sri Lanka Journals Online (SLJOL), Directory of Open Access Journals (DOAJ), Google Scholar and Zoological Records. According to the Google Scholar;H5-Index: 12H5-Median: 15According to the Exaly (1970 – 2021);Impact Factor: 0.6 (top 19%)Extended IF: 0.6 (top 19%)H-Index: 8 (top 28%)Citations/paper: 1.42

TiO2/CdS/CdSe quantum dots co-sensitized solar cell with the staggered-gap (type-II) heterojunctions for the enhanced photovoltaic performance

The effect of co-sensitization and ZnS passivation on the photovoltaic performance of CdS quantum dot sensitized solar cells (QDSSCs) were investigated. The deposition of CdS, CdSe quantum dots (QD) and ZnS passivation on TiO2 photoanode was carried out by successive ionic layer adsorption and reaction (SILAR) method. CdS/CdSe co-sensitization developed two staggered type-II heterojunctions at TiO2/CdS and CdS/CdSe interfaces and resulted a cascade energy band structure. This suitable band alignment facilitated the double charge transfer mechanism at each heterojunction and transported the electrons easily into the photoanode. The narrow bandgap sensitizers CdS and CdSe significantly improved the potential utilization of solar spectrum with more charge carrier generation. ZnS passivation on QD surface suppressed electrode/electrolyte interfacial charge recombination and facilitated more electron injection from QDs into TiO2 photoanode. The EDAX elemental mapping results inferred that CdS, CdSe and ZnS have efficiently covered the TiO2 surface. TiO2/CdS and CdS/CdSe interfaces and the amorphous nature of ZnS could be verified with HRTEM images. Hence, the co-sensitization and surface passivation played a significant role to enhance the PCE of CdS QDSSC from 1.9% to 4.05%.

Efficiency Enhancement by Insertion of ZnO Recombination Barrier Layer in CdS Quantum Dot-Sensitized Solar Cells.

In this investigation we report the formation of thin ZnO recombination barrier layer at TiO₂/CdS interface aimed for the improvement in performance of CdS sensitized solar cell. The film was deposited upon nanocrystalline mesoporous TiO₂ surface by following a simple chemical process and characterized, using UV-Visible spectroscopy, X-ray diffraction and electron dispersive X-ray measurements. The insertion of ZnO thin layer enhances the QDSC (Quantum dot sensitized solar cell) performance, contributed mainly by an increase in open circuit voltage (Voc) due to reduced electron back transfer from TiO₂ conduction band. Moreover, the analysis of photovoltaic characteristics upon increasing the thickness of the ZnO film reveals that the ZnO recombination barrier layer with optimum thickness at porous TiO₂/CdS interface proved to be an effective potential barrier for minimizing electron back recombination.

Antimony tin oxide/lead selenide composite as efficient counter electrode material for quantum dot-sensitized solar cells

Antimony tin oxide (ATO)/lead selenide (PbSe) composite was rationally designed and fabricated on fluorine doped tin oxide glass (FTO) for using as counter electrode (CE) of quantum dot sensitized solar cells (QDSSCs). The electrocatalytic activity of the CE is deeply investigated in the polysulfide electrolyte by employing the Tafel, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) of the symmetrical cells. The results confirm that the ATO/PbSe CE has better electrocatalytic activity and stability than that of PbSe CE obtained by pulse voltage electrodeposition (PVD). The enhanced electrocatalytic performance of ATO/PbSe CE can be attributed to its high specific surface area, excellent permeability, conductivity and interface connectivity, which provide more electrocatalytic active sites for the reduction of polysulfide species, as well as fast channels for ions diffusion and electron transport. As a result, the CdS QDSSCs and CdS/CdSe co-sensitized QDSSCs assembled by the ATO/PbSe CE exhibits better power conversion efficiency (η) of 1.72% and 5.59%, respectively than that of PbSe CE obtained by PVD. Furthermore, photovoltaic property of the ATO/PbSe CE in CdS/CdSe co-sensitized QDSSCs keeps stable for over 200 min. This present work provides a simple and effective strategy for the construction of high-performance CE materials of QDSSCs.

Synthesis of Pb-doped CdS quantum dot using SILAR method on mesoporous TiO2 layer

This research focuses on the fabrication of CdS quantum dot-sensitized solar cells (QDSCs). CdS quantum dots (QDs) were fabricated on a mesoporous TiO2 electrode using a successive ion layer adsorption and reaction (SILAR) method and Pb doping concentrations (0, 2, 4, 10, 15, 20, 25 and 30 %mol) were varied. The change in optical properties of CdS QDs was found to be affected by Pb doping. The Pb-doped CdS QDSCs were determined under the illumination of 100 mWcm−2, which indicated the highest power conversion efficiency (PCE) was 1.73% at 20% Pb dopant.

Carbon quantum dots improving photovoltaic performance of CdS quantum dot-sensitized solar cells

Abstract N-doped carbon quantum dots (CQDs) are introduced into CdS quantum dot-sensitized solar cells (QDSCs) to improve the photovoltaic performance. The fluorescent CQDs with average diameter of 2.97 ± 0.4 nm are prepared using cotton fiber as carbon precursor and urea as dopant by hydrothermal method. The power conversion efficiency (PCE) of CQDs/CdS based QDSCs is 0.606%, which is 40.9% higher than that of CdS based QDSCs (0.430%). There are three reasons for this improvement: (1) the CQDs broaden the absorption range and enhance the absorption intensity of the sensitized photoanode; (2) the CQDs effectively reduce the charge recombination between the photoanode and electrolyte interface in the QDSCs; (3) the CdS quantum dots (QDs) and CQDs are probably forming a band alignment of type I, which makes the LUMO descend from CdS QDs to TiO2 through CQDs.

Enhancement in power conversion efficiency of CdS quantum dot sensitized solar cells through a decrease in light reflection

In this research, the effect of a Magnesium Fluoride (MgF2) Anti-Reflection (AR) layer was investigated in quantum dot sensitized solar cells (QDSCs). MgF2 nanoparticles with the dominant size of 20 nm were grown by a thermal evaporation method and a thin layer was formed on the front side of the fluorine-doped tin oxide (FTO) substrate. In order to study the effect of the AR layer on the efficiency of solar cells, this substrate was utilized in CdS QDSCs. In this conventional structure of QDSC, TiO2 nanocrystals (NCs) were applied on the FTO substrate, and then it was sensitized with CdS quantum dots (QDs). According to the results, the QDSCs with a MgF2 AR layer represented the maximum Power Conversion Efficiency (PCE) of 3%. This efficiency was increased by about 47% compared to the reference cell without the AR layer. The reason is attributed to the presence of the AR layer and the reduction of incident light reflected from the surface of the solar cell.

Investigation of the CdS quantum dot sensitized solar cells based on a series of zinc titanium mixed metal oxides

In this work, a series of zinc titanium mixed metal oxides obtained from the zinc titanium layered double hydroxides as precursor were prepared as the photoanode material of the CdS quantum dot-sensitized solar cells. CdS quantum dots were deposited on photoanodes by the successive ionic adsorption and reaction method. It was investigated that the effects of photoanode based on different Zn–Ti molar ratios on the photovoltaic performance of solar cells. The essential parameters of samples were investigated by UV–vis absorption spectrum, incident photon-to-current conversion efficiency, photoelectric conversion efficiency and electrochemical impendence spectrum. The varying Zn–Ti ratios influence adsorption properties and charge mobility. As a result, the cells based on Zn–Ti MMOs achieved an optimum power conversion efficiency of 2.71% when the Zn–Ti ratio is 7:1.

Effect of PbS quantum dot-doped polysulfide nanofiber gel polymer electrolyte on efficiency enhancement in CdS quantum dot-sensitized TiO2 solar cells

Quantum dot-sensitized solar cells (QDSSCs) are among the most promising low cost third generation solar cells. Semiconductor quantum dots have unique properties such as high molar extinction coefficients, tunable energy gap by the quantum confinement effect and the ability of multiple exciton generation. In this study, stable CdS QDSSCs were fabricated by using polysulfide liquid electrolyte and also by using cellulose acetate nanofiber-based gel electrolyte. Incorporation of PbS Q dots to the liquid or gel electrolyte showed a significant enhancement in solar cell efficiency. Under the simulated light of 100 mW cm−1 the efficiency of the polysulfide liquid electrolyte based CdS QD solar cells increased from 1.19% to 1.51% and the efficiency of the nanofibre gel electrolyte based CdS QD solar cells increased from 0.94% to 1.46% due to the incorporation of 5% (wt/wt) PbS Q dots into the respective electrolytes. The efficiency increase has been attributed to the increase in short circuit photocurrent density due to increased sulfide ion (S2−) conductivity evidently caused by indirect ionic dissociation facilitated by PbS QDs.

Preparation of CdS quantum dot sensitized solar cell based on ZnTi-layered double hydroxide photoanode to enhance photovoltaic properties

One of the most important factors in low power conversation efficiency of quantum dot sensitized solar cells (QDSSCs) is the electron-hole recombination. A photoanode composed of CdS QDs deposited on ZnTi layered double hydroxide film was fabricated to enhance the photovoltaic performance of CdS QDSSCs. The performance of fabricated photoanode in the QDSSCs is compared with TiO2/CdS photoanode. The results show that the application of the ZnTi-LDH considerably enhance the light harvesting and electron-hole separation efficiency. The energy conversion efficiency of 3.92% is obtained using the QDSSC fabricated based on the ZnTi-LDH/CdS photoelectrode, under the illumination of one sun (AM1.5, 100 mW/cm2). The achieved efficiency is higher than the efficiency of usual QDSSCs assembled by TiO2/CdS photoanode (1.91%).

Alloying cadmium cobalt sulfide quantum dots for solar cells applications

In this work, controlling the optical band gap of alloyed cadmium cobalt sulfide quantum dots (QDs) for solar cells applications is studied. Different cobalt molar ratios (x: 0, 0.1, 0.2, 0.3 and 0.4) of ternary alloyed Cd1-xCoxS QDs have been synthesized onto TiO2 nanoparticles (Titania NPs) electrodes using successive ionic layer adsorption and reaction (SILAR) technique. Transition electron microscope (TEM) has been utilized to characterize the morphological properties of the prepared photoanodes. The structural properties are studied using an X-ray diffractometer. The optical properties of the prepared photoanodes have been measured using a UV–visible spectrophotometer. The energy band gap of the prepared alloyed Cd1-xCoxS photoanodes is systematically red-shifted as the cobalt molar ratio increases. This novel result is discussed in terms of the effective incorporation of cobalt material and Moss-Burstein effect. To the best of our knowledge, the optical bowing parameter (b) of the ternary alloyed Cd1-xCoxS QDs has been determined and equals 0.96 ± 0.14 eV using the modified Vegard's approach for the first time. The prepared alloyed Cd1-xCoxS photoanodes are used for photovoltaic applications. Alloyed Cd0.9Co0.1S QDs sensitized solar cells (QDSSCs) show better photovoltaic performance than bare CdS QDSSC and other rest alloyed Cd1-xCoxS QDSSCs. This result is mainly attributed to the enhancement in the absorption of the solar spectrum and to the good harmonizing of the energetic alignment levels of the QDSSCs’ components. The reproducibility and sensitivity of the assembled QDSSCs undercutting on-off solar illumination are also studied.

Er-doped carbon dots broadening light absorption range and accelerating electron transport for enhancing photovoltaic performance of CdS quantum dots sensitized cells

In this paper, Er-doped carbon quantum dots (Er-CQDs) is first incorporated into CdS quantum dot sensitized solar cells (QDSSCs) for broadening light absorption range and accelerating electron transport. Er-CQDs are prepared by hydrothermal method forming Er-CQDs/TiO2 film. The CdS quantum dots (QDs) are deposited on Er-CQDs/TiO2 film by successive ionic layer adsorption and reaction (SILAR) method, constituting CdS/Er-CQDs/TiO2 photoanode. The structural and optical properties of the CQDs and CdS/Er-CQDs/TiO2 photoanode are characterized by FT-IR, UV–vis, FL and PL techniques. The composition and morphology are confirmed by XRD, EDX, SEM and TEM techniques. The optical properties of the influence of Er-CQDs on photovoltaic performance of CdS QDSSCs is studied by electrochemical methods. The experiment data show that the photovoltaic performance of CdS/Er-CQDs/TiO2 working electrode can greatly be enhanced compared that of CdS/TiO2. In comparison, the PCE increases from 0.34% of CdS/TiO2 device to 0.43% of CdS/CQDs/TiO2 device, whose escalating rate is 26.45%. Furthermore, the PCE increases from 0.34% of CdS/TiO2 device to 0.59% of CdS/Er-CQDs/TiO2 device, whose escalating rate reaches 73.53%.

The Stability of CdS QDSCs Based on Optimized MWCNs/CuS Counter Electrodes

In order to enhance the stability of CdS quantum dot sensitized solar cells (QDSCs), the CdS quantum dots (QDs) sensitizer is loaded with ZnS QDs as a passivation layer and Pt counter electrode (CE) material is replaced by multiwall carbon nanotubes (MWCNTs) combined with CuS QDs. The microstructure of CEs is observed by SEM and TEM. The results show acid-treated MWCNTs can possess a larger specific surface area resulting in loading more CuS QDs. CuS QDs with uniform nanometer size are deposited on the external wall of acid-treated MWCNTs. The electrocatalytic activity of CEs is analyzed by electrochemical impedance spectroscopy (EIS) and Tafel curves. The results exhibit that the electrocatalytic activity of acid-treated MWCNTs improves after the introduction of CuS QDs. Under 24 h one-sun illumination, the electrocatalytic activity of Pt CEs decreases remarkably, even less than acid-treated MWCNTs/CuS QDs CEs. The photoelectric property of QDSCs is analyzed with J–V curves. The photoelectric parameters of QDSCs can be improved considerably after loading CuS QDs into acid-treated MWCNT CEs. Power conversion efficiency (PCE) of the QDSC with acid-treated MWCNTs/CuS QDs CE is lower than that of Pt CE based one, but after 24 h one-sun illumination, it does not change in comparison with sharp PCE degradation of the Pt CE based QDSC. The mechanism of improved QDSC stability is discussed systematically through optimizing the CEs.

Impact of composition of polysulphide electrolyte on the photovoltaic performance in quantum dot sensitized solar cells

Sustained and efficient photovoltaic action depends on the electrolyte employed in the device like Quantum Dot Sensitized Solar cell (QDSSC). The study here focuses on the comparison of performance of different polysulphide electrolytes in CdS QDSSC by virtue of difference in their composition. Systematic electrochemical analyses were performed to study the effect of electrolyte composition on the overall solar cell performance by employing chronoamperometry, electrochemical impedance spectroscopy and electrical characterization of the fabricated solar cells. Of all the composition of electrolytes considered here, a modified polysulphide electrolyte with combination of ethanol, methanol and water has emerged as the best.

A reduced graphene oxide interface layer for improved power conversion efficiency of aqueous quantum dots sensitized solar cells

Abstract In quantum dots sensitized solar cells (QDSSCs), the back-transport reaction, resulting from the recombination between the photo-generated electrons in transparent conductive oxide (TOC) substrates and the polysulfide species electrolytes, significantly impairs the power conversion efficiency. To solve this, a reduced graphene oxide (rGO) interface layer has been for the first time introduced between the TOC substrate and the porous TiO2 film in a modified CdS QDSSC by a spray-coating method. This rGO interface layer can effectively suppress the back-transport reaction by inhibiting the contact between TOC substrates and electrolytes. Consequently, an improvement in power conversion efficiency of ca. 20% has been achieved on the solar cell. Besides, an interesting threshold effect has also been found on this interface layer, which leads to much variated behavior of this rGO layer on the suppression of the back-transport reaction. Consequently, the optimum rGO interface layer has been obtained with a spray time of 2 min, which leads to the best photovoltaic properties.

Growth of ZnO nanowires and their applications for CdS quantum dots sensitized solar cells

ZnO nanowires grown on ITO conductive glass substrates by chemical bath deposition (CBD) method were used as photoanodes to assemble the CdS quantum dots sensitized solar cells (QDSSCs). The growth mechanism of ZnO nanowires and the photovoltaic performance of CdS QDSSCs were investigated. The results show that the c-axis oriented seed layer and the growth process both contribute to the preferential alignment of ZnO nanowires along the [0001] direction. The average length and diameter of nanowires increase with increasing growth time, and the maximum aspect ratio is 20.56 at 9h. CdS quantum dots deposited on ZnO nanowires enhance the absorbance and extend the absorption range to the visible region. ZnO nanowires with higher aspect ratio effectively increase the energy conversion efficiency (η) of CdS QDSSCs, and the best η is 0.401% with an aspect ratio of 20.56. In such a solar cell, the short-circuit current density is significantly improved due to more electron-hole pairs and strong light trapping effect of ZnO nanowires.

Optimization of the Photoanode of CdS Quantum Dot-Sensitized Solar Cells Using Light-Scattering TiO2 Hollow Spheres

CdS quantum dot-sensitized solar cells (QDSCs) have been fabricated and their photoanode optimized by altering the thickness of the photoelectrode and CdS deposition conditions and applying a ZnS electron-blocking layer and TiO2 hollow spheres. Hydrothermally grown TiO2 nanocrystals (NCs) with dominant size of 20 nm were deposited as a sublayer in the photoanode with thickness in the range from 5 μm to 10 μm using a successive ionic layer adsorption and reaction (SILAR) method. The number of deposition cycles was altered over a wide range to obtain optimized sensitization. Photoanode thickness and number of CdS sensitization cycles around the optimum values were selected and used for ZnS deposition. ZnS overlayers were also deposited on the surface of the photoanodes using different numbers of cycles of the SILAR process. The best QDSC with the optimized photoelectrode demonstrated a 153% increase in efficiency compared with a similar cell with ZnS-free photoanode. Such bilayer photoelectrodes were also fabricated with different thicknesses of TiO2 sublayers and one overlayer of TiO2 hollow spheres (HSs) with external diameter of 500 nm fabricated by liquid-phase deposition with carbon spheres as template. The optimization was performed by changing the photoanode thickness using a wide range of CdS sensitizing cycles. The maximum energy conversion efficiency was increased by about 77% compared with a similar cell with HS-free photoelectrode. The reason was considered to be the longer path length of the incident light inside the photoanode and greater light absorption. A ZnS blocking layer was overcoated on the surface of the bilayer photoanode with optimized thickness. The number of CdS sensitization cycles was also changed around the optimized value to obtain the best QDSC performance. The number of ZnS deposition cycles was also altered in a wide range for optimization of the photovoltaic performance. It was shown that the maximum efficiency was increased by about 55% compared with a similar QDSC with ZnS-free bilayer photoanode. The final improvement was carried out by applying methanol-based Cd precursor solution in the SILAR deposition process. The best photoanodes from the previous stages were selected and used in this sensitizing process. Besides, nanocrystalline TiO2 sublayers with different thicknesses were applied for further optimization. The results revealed that maximum power conversion efficiency of 3.7% was achieved as a result of such improvement, for a QDSC with optimized double-layer photoanode including TiO2 HSs and NCs and ZnS blocking layer.

A novel method for fabrication of CdS quantum dot-sensitized solar cells

In this report, a novel and facile in situ gas–solid reaction method has been developed for the deposition of CdS quantum-dots (QDs) on a mesoscopic TiO2 film. In the approach, cadmium nitrate solution was first coated on mesoporous TiO2 films, and subsequently transformed into CdS QDs (with size about 2–3 nm) by reaction with hydrogen sulfide (H2S) gas generated in a closed container at room temperature. Different from the conventional solution techniques, this method offers new opportunities for rapid and facile deposition of CdS QD-coated TiO2 films without the introduction of the by-products. With the CdS QDs-decorated TiO2 active electrodes, the liquid and solid solar cells were fabricated with power conversion efficiencies (PCEs) of 1.90 and 0.80%, respectively.

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.