CdS Quantum Dot-sensitized Solar Cells Research Articles

Enhancing the efficiency of CdS quantum dot-sensitized solar cells via electrolyte engineering

Quantum dot-sensitized solar cells (QDSSCs) are one kind of promising photovoltaic devices for harvesting solar energy. Previous reports have studied various photoanode materials in order to achieve a high photoelectric performance, while little attention has been paid to the electrolyte system inside the QDSSCs. In this report, a polysulfide (S2−/Sx2−) electrolyte system was investigated and optimized based on a CdS quantum dot/ZnO nanowire solar cell and a CdSe/CdS co-sensitized QDSSC. Water–methanol mixed solution was taken as the solvent for this polysulfide electrolyte, considering simultaneously the penetration ability and the ion dissociation of the electrolyte. Electrochemical impedance spectra (EIS) measurement was used to investigate the impedance of the electrons recombination with the electrolyte at the photoanode/electrolyte interface. With the measured efficiency of the CdS-QDSSCs, the optimal composition of the electrolyte can be obtained. The work facilitates the development of highly-efficient electrolyte in the general field of quantum dot-sensitized solar cells.

Mesoporous titanium oxide microspheres for high-efficient cadmium sulfide quantum dot-sensitized solar cell and investigation of its photovoltaic behavior

Mesoporous TiO2 microspheres with large surface area are synthesized by a hydrothermal reaction of titanium glycolate, and then introduced into CdS quantum dot-sensitized solar cell (QDSC). These mesoporous TiO2 microspheres can not only increase the adsorption amount of quantum dots (QDs), but also possess effective light scattering ability due to the proper size, in comparison with traditional TiO2 (P25). An overall power conversion efficiency of 2.63% is achieved by using these mesoporous TiO2 microspheres as electrode in QDSC, significantly higher than that derived from P25 TiO2 electrode. In addition, the photovoltaic behaviors of the materials are studied by surface photovoltage measurement to explain the excellent performance of QDSCs.

Long afterglow Sr4Al14O25:Eu,Dy phosphors as both scattering and down converting layer for CdS quantum dot-sensitized solar cells.

Long afterglow Sr4Al14O25:Eu,Dy phosphors were introduced into the TiO2 photoanode of CdS quantum dot-sensitized solar cells (QDSSCs) as both a scattering and down converting layer, and the photovoltaic performances of the cells were investigated. The results show that the cell with Sr4Al14O25:Eu,Dy achieves a power conversion efficiency of 1.40%, which is an increase of 38% compared to the cell without Sr4Al14O25:Eu,Dy (1.02%). The performance improvement is attributed to enhanced light harvesting via improved light absorption and scattering processes. After a single sun illumination for 1 min and subsequent removal of the light source, the cell with Sr4Al14O25:Eu,Dy could be driven even in the dark by the long persistent light from Sr4Al14O25:Eu,Dy.

Improved efficiency of CdS quantum dot sensitized solar cell with an organic redox couple and a polymer counter electrode

Quantum dot sensitized solar cells (QDSSCs) based on an organic thiolate/disulfide redox couple (C7H5N4S-/C14H10N8S2 or C2H3N4S-/C4H6N8S2) and a polymer counter electrode [poly (3, 4-ethylenedioxythiophene), PEDOT] were fabricated and their photovoltaic performance were investigated. In CdS QDSSC, the organic C7H5N4S-/C14H10N8S2 electrolyte shows better performance than the polysulfide electrolyte, and the PEDOT counter electrode exhibits higher efficiency than that of the Pt counter electrode and the CoS counter electrode. An efficiency of 1.53% was achieved in this QDSSC. The influences of the morphology and the deposition charge of the PEDOT counter electrodes on the cell performance were also studied. Furthermore, it was found that the C7H5N4S-/C14H10N8S2 redox couple outperformed the C2H3N4S-/C4H6N8S2 redox couple due to reduced electron recombination.

Effect of cationic groups in organic sulfide electrolyte on the performance of CdS quantum dot sensitized solar cells

Two organic sulfide redox couples derived from 2-mercapto-5-methyl-1,3,4-thiadiazole (McMT): tetrabutylammonium thiolate (McMT−TBA+)/disulfide dimer (BMT) and tetramethylammonium thiolate (McMT−TMA+)/BMT were incorporated into quantum dots sensitized solar cells (QDSCs) as alternatives to the inorganic polysulfide electrolyte (Na2S/S). It was found in symmetrical cells test that the interfaces of the organic sulfide electrolytes/platinum counter-electrode have much lower charge transfer resistances as well as higher interface reaction rates compared with that for the inorganic one. Besides, QDSCs based on organic sulfide electrolytes exhibited obviously higher fill factors, open circuit photovoltages, and therefore higher conversion efficiency, thanks to the prohibited recombination and lower redox potential. In addition, by comparing and analyzing the performance of devices based on organic sulfide electrolytes with different cationic groups, it is found that cationic group TMA+ with smaller size was favorable for the mass transport in the electrolyte, which explains the better photovoltaic performance of McMT−TMA+/BMT based solar cell than that of McMT−TBA+/BMT based one. Eventually, a power conversion efficiency (PCE) of 0.63 % was achieved for QDSCs using McMT−(TMA+)/BMT redox couple as electrolyte, which was till now the highest for CdS QDSC based on organic sulfide electrolyte.

Synthesis of Cu2ZnSnS4 Nanoparticles for Applications as Counter Electrodes of CdS Quantum Dot-Sensitized Solar Cells

Cu2ZnSnS4 (CZTS) nanoparticles have been synthesized through a one-step solvothermal route, which exhibited a nearly single kesterite structure with a fundamental band gap of ∼1.54 eV. Quantum dots-sensitized solar cells were fabricated based on CZTS counter electrodes and CdS QD-sensitized TiO2 NRs photoelectrodes with various thicknesses of QD sensitization layers. The cells based on a CZTS electrode, compared with other single-layer DSSCs in this study, had the highest conversion efficiency of 0.27% (for CdS layer numbers of 9), which was obviously higher than Pt. The performance improvement was attributed to the better stability, sunlight sensitivity, and the resulting photoelectrocatalytic activity of the CZTS electrodes.

CdS quantum dot-sensitized solar cells based on nano-branched TiO2 arrays

Nano-branched rutile TiO2 nanorod arrays were grown on F:SnO2 conductive glass (FTO) by a facile, two-step wet chemical synthesis process at low temperature. The length of the nanobranches was tailored by controlling the growth time, after which CdS quantum dots were deposited on the nano-branched TiO2 arrays using the successive ionic layer adsorption and reaction method to make a photoanode for quantum dot-sensitized solar cells (QDSCs). The photovoltaic properties of the CdS-sensitized nano-branched TiO2 solar cells were studied systematically. A short-circuit current intensity of approximately 7 mA/cm2 and a light-to-electricity conversion efficiency of 0.95% were recorded for cells based on optimized nano-branched TiO2 arrays, indicating an increase of 138% compared to those based on unbranched TiO2 nanorod arrays. The improved performance is attributed to a markedly enlarged surface area provided by the nanobranches and better electron conductivity in the one-dimensional, well-aligned TiO2 nanorod trunks.

Efficiency improvement of CdS and CdSe quantum dot-sensitized solar cells by TiO2 surface treatment

CdS and CdSe quantum dots (QDs) have been synthesized via successive ionic layer adsorption and reaction for the fabrication of quantum dot-sensitized solar cells (QDSSCs). In this work, several approaches such as incorporation of ZnS passivation layer, scattering layer, treatment with TiCl4, and increasing the TiO2 layer thickness have been applied on TiO2 layer in order to improve the solar cell performance. By passivating the QD-sensitized TiO2 layer with ZnS, the performance of the cells increased due to reduction of charge recombination at the photoanode/electrolyte interface. With a thicker TiO2 layer thickness of 26 μm, further enhancement was observed. The efficiency of the CdS and CdSe QDSSCs improved from 1.06% to 1.48% and from 1.41% to 3.05%, respectively. On the other hand, scattering layer and treatment with TiCl4 did not bring much improvement to the cells.

Improved performance of CdS and dye co-sensitized solar cell using a TiO2sol-gel solution

An interfacial layer (IL) between the CdS quantum dot (QD) and dye is necessary in the CdS-dye co-sensitized solar cell (CSC) to prevent the corrosion of CdS and the damage of electrolyte. In this study, the simple method of using a TiO2 sol–gel solution is suggested to fabricate the IL. An air exposure process after dipping into the TiO2 sol–gel solution facilitates formation of the anatase TiO2 thin film. To confirm the effect of TiO2 IL, the performance of CdS-dye CSC is analyzed and compared to the conventional CdS QD sensitized solar cell (QDSC). The formed TiO2 IL effectively prevents the corrosion of CdS and the damage of electrolyte. In addition, this suppresses the electron recombination from the CdS to the electrolyte, resulting in the enhanced electron transport at the TiO2/CdS QD-dye/electrolyte interface. As a result, the overall photovoltaic performance is much increased from 1.33% to 2.77%, compared to the conventional CdS QDSC.

Performances of some low-cost counter electrode materials in CdS and CdSe quantum dot-sensitized solar cells.

Different counter electrode (CE) materials based on carbon and Cu2S were prepared for the application in CdS and CdSe quantum dot-sensitized solar cells (QDSSCs). The CEs were prepared using low-cost and facile methods. Platinum was used as the reference CE material to compare the performances of the other materials. While carbon-based materials produced the best solar cell performance in CdS QDSSCs, platinum and Cu2S were superior in CdSe QDSSCs. Different CE materials have different performance in the two types of QDSSCs employed due to the different type of sensitizers and composition of polysulfide electrolytes used. The poor performance of QDSSCs with some CE materials is largely due to the lower photocurrent density and open-circuit voltage. The electrochemical impedance spectroscopy performed on the cells showed that the poor-performing QDSSCs had higher charge-transfer resistances and CPE values at their CE/electrolyte interfaces.

Fabrication, Characterization, and Optimization of CdS and CdSe Quantum Dot-Sensitized Solar Cells with Quantum Dots Prepared by Successive Ionic Layer Adsorption and Reaction

CdS and CdSe quantum dot-sensitized solar cells (QDSSCs) were used for the study of determining the optimum preparation parameters that could yield the best solar cell performance. The quantum dots (QDs) were coated on the surface of mesoporous TiO2layer deposited on FTO substrate using the successive ionic layer adsorption and reaction (SILAR) method. In this method the QDs are allowed to grow on TiO2by dipping the TiO2electrode successively in two different solutions for predetermined times. This method allows the fabrication of QDs in a facile way. Three preparation parameters that control the QD fabrication were investigated: concentration of precursor solutions, number of dipping cycles (SILAR cycles), and dipping time in each solution. CdS based QDSSC showed optimum performance when the QDs were prepared from precursor solutions having the concentration of 0.10 M using 4 dipping cycles with the dipping time of 5 minutes in each solution. For CdSe QDSSC, the optimum performance was achieved with QDs prepared from 0.03 M precursor solutions using 7 dipping cycles with 30 s dipping time in each solution. The QDs deposited on TiO2surface were characterized using UV-vis absorption spectroscopy, FESEM, and TEM imaging.

Enhanced photovoltaic performance utilizing effective charge transfers and light scattering effects by the combination of mesoporous, hollow 3D-ZnO along with 1D-ZnO in CdS quantum dot sensitized solar cells

A combination of 3-dimensional (3D) hollow mesoporous ZnO microspheres (ZnO HMSP) and vertically grown one-dimensional ZnO nanowires (1D ZnO NWs) on a fluorine doped tin oxide (FTO) coated glass substrate has been investigated as a photoanode for a CdS quantum dot-sensitized solar cell (QSSC). A comparative study of the photovoltaic performance of the solar cell with devices fabricated with pristine ZnO HMSPs and ZnO NWs was carried out. The proposed photovoltaic device exhibits an enhancement in power conversion efficiency (PCE) upto ∼74% and ∼35%, as compared to the 1D ZnO NW and ZnO HMSP based solar cells. The maximum incident photon-to-current conversion efficiency (IPCE) for the solar cell was observed to be ∼40%, whereas for the devices fabricated with bare ZnO HMSP and ZnO NW the IPCE were only ∼32% and ∼19%, respectively. The enhanced photovoltaic performance of the solar cell is attributed to the high Brunauer-Emmett-Teller (BET) surface area, efficient light-scattering effects and facilitated diffusion of the electrolyte for better functioning of the redox couple (S(2-)/Sn(2-)) in the hybrid photoanode. Moreover, a faster electron transport through 1D ZnO NWs provides better charge collection from the photoactive layer, which leads to an increase in the short circuit current density of the device. The present study highlights the design and development of a new hybrid photoanode for solar harvesting.

Influence of Cationic Precursors on CdS Quantum-Dot-Sensitized Solar Cell Prepared by Successive Ionic Layer Adsorption and Reaction

Successive ionic layer adsorption and reaction (SILAR) is the most extensively used method for the direct and simultaneous synthesis and deposition of quantum dots (QDs) onto porous oxide films for quantum-dot-sensitized solar cell (QDSC) applications. In this work, the noticeable influences of the cationic precursors on the deposition of CdS QDs and the QDSC performance have been studied. A careful comparison of two cationic precursors, cadmium nitrate and cadmium acetate, for the preparation of CdS QDSCs by the SILAR method showed that, compared to the commonly used cadmium nitrate, cadmium acetate provided a significantly higher deposition rate of CdS QDs on TiO2 films. A solar cell power conversion efficiency of 2.15% was achieved for a CdS QDSC employing cadmium acetate as the cationic precursor, much higher than the value of 1.44% obtained for the cell prepared using cadmium nitrate for the same number of SILAR cycles. Control experiments in which the recipes of the cationic precursor solutions were...

Synthesis and Characterization of Graphene-ZnO Nanocomposite and its Application in Photovoltaic Cells

In this paper, we present a simple method for preparation of graphene-ZnO nanocomposites (G-ZnO). The method is based on thermal treatment of the graphene oxide (GO)/ZnO paste which reduces the graphene oxide into the graphene and leads to the formation of the G-ZnO nanocomposite. The structure, morphology and optical properties of synthesized nanocomposites are characterized with XRD, FESEM, FTIR and Raman spectroscopies. Here CdS quantum dots are deposited on G-ZnO nanocomposite structure and is integrated as a photoanode in CdS quantum dot sensitized solar cells (QDSSCs). Photovoltaic properties of CdS QDSSC based on bare ZnO nanoparticles and G-ZnO nanocomposite photoanodes are studied here. The cell with G-ZnO/CdS photoanode shows two times higher photoelectric conversion efficiency than that of the pure ZnO photoanode (0.94 vs. 0.45).

Effect of architectures assembled by one dimensional ZnO nanostructures on performance of CdS quantum dot-sensitized solar cells

Effect of ZnO architectures on photoelectric conversion efficiency of CdS quantum dot-sensitized ZnO solar cells is investigated. Four kinds of architecture assembled by one dimensional ZnO nanostructures, including ZnO nanorod arrays, nanotube arrays, forest, and pyramid arrays formed by thin nanowires, are designed and fabricated as photoanodes. Light-to-electricity conversion efficiency of these cells is 1.60% for the pyramid arrays, 1.34% for the forest, 1.08% for the nanotube arrays and 0.50% for the nanorod arrays, respectively, indicating that the architecture strongly affects the photoelectric conversion efficiency. Absorption spectra, dark current curves and photoelectron decay are measured to analyze the causes of differences. We find that light absorption and photoelectron transmission from ZnO nanostructures to FTO substrate are important factors for the cells. As the ZnO pyramid arrays formed by thin nanowires have anti-reflection character, high specific area for deposition of CdS sensitizer and fast photoelectron transmission channels to FTO substrate, higher photoelectric conversion efficiency is achieved. This investigation is important to the improvement on conversion efficiency for quantum dot-sensitized solar cells.

Surface treatment properties of CdS quantum dot-sensitized solar cells

The dye-sensitized solar cells (DSSCs) are attractive due to their low cost and promising efficiency. One of the research perspectives in the respective field is to replace the expensive and photodegradable ruthenium metal-based dyes. Present work describes a simple, modified in situ route designed by mimicking the adsorption principle of dyes in DSSCs for surface modification and linking of CdS-Quantum Dots (QDs) to TiO2 electrode. An organic compound 2-mercaptoethanol (ME) was used as a surface modifying and linking agent. By following this route it was expected to get a well assembled layer of CdS QDs for better cell performance but performances were not as expected. The main reason for low photocurrent density is the partial coverage of QDs surface by ME and the spatial distance between QDs and TiO2 electrode. Additional surface treatment of the CdS QDs sensitized TiO2 electrode resulted in an increase in the photocurrent density and photovoltage. This indicates that ME is not an effective capping agent and thus partially covers the QDs surface. The remaining sites, not covered by ME were passivated by sulfur ions in the ionic solution.

Improvement of photocurrent generation of Ag2S sensitized solar cell through co-sensitization with CdS

In this study, photovoltaic application of Ag2S-CdS heterostructure is reported. The photovoltaic cell generated considerably high photocurrent density (Jsc) of 27.6 mA/cm2, which is over two times larger than that of the Ag2S quantum dot sensitized solar cell (QDSSC) of 11.3 mA/cm2. This improvement is due to the cascade-shaped band structure alignment of ZnO/CdS/Ag2S and to the excellent role of CdS as a buffer layer for relieving lattice mismatch. The power conversion efficiency of the CdS/Ag2S QDSSC, which was attributed to the superior Jsc, was 2.4%, twice as high as the 1.2% efficiency of the Ag2S QDSSC and the CdS QDSSC.

Improving the performance of quantum dot-sensitized solar cells by using TiO2 nanosheets with exposed highly reactive facets

We demonstrated CdS quantum dot-sensitized solar cells (QDSSCs) based on anatase TiO2 nanosheets with exposed {001} and {100} facets. Under the illumination of one Sun (AM 1.5 G, 100 mW cm−2), the photovoltaic conversion efficiencies were 2.29% for a QDSSC based on {001}-TiO2 nanosheets, 2.18% for a QDSSC based on {100}-TiO2 nanosheets, and 1.46% for a QDSSC based on commercial Degussa P25. It was found that the exposed highly reactive facets of TiO2 nanosheets had a remarkable influence on the QDSSCs due to their better adsorption abilities for QDs, leading to the high short current density and the enhanced photovoltaic performance.

Long afterglow SrAl2O4:Eu,Dy phosphors for CdS quantum dot-sensitized solar cells with enhanced photovoltaic performance

An efficient bifunctional structured layer composed of long afterglow SrAl2O4:Eu,Dy phosphors on top of a transparent layer of nanocrystalline TiO2 was fabricated for use in CdS quantum dot-sensitized solar cells (QDSSCs). The introduction of SrAl2O4:Eu,Dy increases the photocurrent of the QDSSCs mainly due to enhanced light harvesting abilities via improved light absorption and scattering. Under one sun illumination (AM 1.5G, 100 mW cm−2), cells containing SrAl2O4:Eu,Dy show a marked improvement in their conversion efficiency (1.24%) compared with cells without SrAl2O4:Eu,Dy (0.98%). After one sun illumination for 1 min, after which the light source was turned off, cells containing SrAl2O4:Eu,Dy show an efficiency of 0.07% under dark conditions due to the irradiation by the long persistent light from SrAl2O4:Eu,Dy. The present strategy should provide a possibility to fulfil the operation of solar cells even in the dark.

Synthesis of ZnO nanorods and their application in quantum dot sensitized solar cells

ZnO nanorod thin films of different thicknesses and CdS quantum dots have been prepared by chemical method. X-ray diffraction pattern reveals that the CdS quantum dot and ZnO nanorods are of hexagonal structure. Field emission scanning electron microscope images show that the diameter of hexagonal shaped ZnO nanorods ranges from 110 to 200 nm and the length of the nanorod vary from 1.3 to 4.7 μm. CdS quantum dots with average size of 4 nm have been deposited onto ZnO nanorod surface using successive ionic layer adsorption and reaction method and the assembly of CdS quantum dot with ZnO nanorod has been used as photo-electrode in quantum dot sensitized solar cells. The efficiency of the fabricated CdS quantum dot-sensitized ZnO nanorod-based solar cell is 1.10 % and is the best efficiency reported so far for this type of solar cells.