Flexible quantum dot sensitized solar cell by electrophoretic deposition of CdSe quantum dots on ZnO nanorods

We report on a flexible quantum dot-sensitized solar cell (QDSSC) based on ZnO nanorods with a length of 2 μm. Due to the good coverage of CdSe QDs on ZnO by the electrophoretic deposition method, a maximum power conversion efficiency of ～1% is achieved for the flexible QDSSC.     

Controllable synthesis of CdS quantum dots and their photovoltaic application on quantum-dot-sensitized ZnO nanorods

Journal of Solid State Electrochemistry - Water-dispersible l-cysteine (l-cys)-capped cadmium sulfide (CdS) quantum dots (QDs) with a cubic structure and excellent crystallinity are synthesized by...     

A quantum dot sensitized solar cell based on vertically aligned carbon nanotube templated ZnO arrays

We report on a quantum dot sensitized solar cell (QDSSC) based on ZnO nanorod coated vertically aligned carbon nanotubes (VACNTs). Electrochemical impedance spectroscopy shows that the electron lifetime for the device based on VACNT/ZnO/CdSe is longer than that for a device based on ZnO/CdSe, indicating that the charge recombination at the interface is reduced by the presence of the VACNTs. Due to the increased surface area and longer electron lifetime, a power conversion efficiency of 1.46% is achieved for the VACNT/ZnO/CdSe devices under an illumination of one Sun (AM 1.5G, 100 mW/cm²).     

CdS and CdSe quantum dots subsectionally sensitized solar cells using a novel double-layer ZnO nanorod arrays

We report a novel approach for synthesizing CdS and CdSe quantum dots subsectionally sensitized double-layer ZnO nanorods for solar cells, which are comprised of CdS QDs-sensitized bottom-layer ZnO NRs and CdSe QDs-sensitized top-layer ZnO NRs. X-ray diffraction study and scanning electron microscopy analysis indicate that the solar cells of subsectionally sensitized double-layer ZnO NRs, which are the hexagonal wurtzite crystal structure, have been successfully achieved. The novel structure enlarged the range of absorbed light and enhanced the absorption intensity of light. The I-V characteristics show that the double-layer structure improved both the current density (J_sc) and fill factor (FF) by 50%, respectively, and power conversion efficiency (η) was increased to twice in comparison with the CdS QDs-sensitized structure.     

Comparison of two types of vertically aligned ZnO NRs for highly efficient polymer solar cells

Vertically aligned ZnO nanorods (NR) are prepared by two different syntheses methods and applied on polymer solar cells (PSCs). The ZnO electrodes work as the electron transport layer with the P3HT:PCBM blend acting as the active material. Several organic blend solution conditions are optimized: concentration, solvent, and deposition speed. The effect of different NR electrode morphologies is analyzed on the solar cell performance and characterized by current–voltage curves and IPCE analyses. The photovoltaic performance of the solar cells was observed to be influenced by many factors, among them infiltration of the organic P3HT:PCBM blend within the ZnO NR layer. The infiltration of the active layer was monitored by cross section SEM and energy dispersive X-ray spectroscopy analyses. Our results show that higher power conversion efficiencies are achieved when shorter NRs lengths are applied. The best power conversion efficiency obtained was 2.0% for a 400 nm ZnO NR electrode. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Low-temperature growth of ZnO nanorods by chemical bath deposition

Aligned ZnO nanorod arrays were synthesized using a chemical bath deposition method at normal atmospheric pressure without any metal catalyst. A simple two-step process was developed for growing ZnO nanorods on a PET substrate at 90-95 degrees C. The ZnO seed precursor was prepared by a sol-gel reaction. ZnO nanorod arrays were fabricated on ZnO-seed-coated substrate. The ZnO seeds were indispensable for the aligned growth of ZnO nanorods. The ZnO nanorods had a length of 400-500 nm and a diameter of 25-50 nm. HR-TEM and XRD analysis confirmed that the ZnO nanorod is a single crystal with a wurtzite structure and its growth direction is [0001] (the c-axis). Photoluminescence measurements of ZnO nanorods revealed an intense ultraviolet peak at 378.3 nm (3.27 eV) at room temperature.     

Toward highly efficient CdS/CdSe quantum dots-sensitized solar cells incorporating ordered photoanodes on transparent conductive substrates

A series of ordered photoanodic architectures (including ordered TiO(2) nanotube arrays (TNT), ZnO nanorods, ZnO/TiO(2) core/shell nanostructures) for CdS/CdSe sensitized solar cells (QDSCs), were fabricated directly on transparent conductive oxide glasses by a facile sol-gel assisted template process. The morphologies, optical and electrical properties of TNTs and CdS/CdSe co-sensitized TNTs have been demonstrated. The effect of CdSe deposition time on the cell performance was clarified, and the growth mechanism of the CdSe quantum dots on the surface of the TNTs has been proposed as well. Furthermore, the evolution of open-circuit photovoltage (V(oc)) towards CdSe deposition time has been investigated by electrochemical impedance spectroscopy (EIS). A promising light-to-electricity conversion efficiency of up to 4.61% has been achieved with 3 μm long TNT arrays, which is the best record for sandwich-type ordered TNT-based QDSCs.     

Incorporation of graphene in quantum dot sensitized solar cells based on ZnO nanorods

We demonstrate a novel architecture of solar cell by incorporating graphene thin film in a quantum dot sensitized solar cell. Quantum dot sensitized nanorods with a graphene layer exhibited a 54.7% improvement comparing a quantum dot sensitized ZnO nanorods without graphene layer. A fill factor as high as ～62% was also obtained.     

P3HT as hole transport material and assistant light absorber in CdS quantum dots-sensitized solid-state solar cells

Regioregular poly(3-hexylthiophene) (P3HT) was employed as a hole transport material and assistant light absorber for the fabrication of a CdS quantum dot-sensitized solid-state solar cell, by which a power-conversion efficiency of 1.42% was achieved under an AM1.5 G (100 mW cm(-2)) condition.     

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.     

High-efficiency cascade CdS/CdSe quantum dot-sensitized solar cells based on hierarchical tetrapod-like ZnO nanoparticles

Quantum dot-sensitized solar cells (QDSCs) constructed using cascade CdS/CdSe sensitizers and the novel tetrapod-like ZnO nanoparticles have been fabricated. The cascade co-sensitized QDSCs manifested good electron transfer dynamics and overall power conversion efficiency, compared to single CdS- or CdSe-sensitized cells. The preliminary CdS layer is not only energetically favorable to electron transfer but behaves as a passivation layer to diminish the formation of interfacial defects during CdSe synthesis. On the other hand, the anisotropic tetrapod-like ZnO nanoparticles, with a high electron diffusion coefficient, can afford a better carrier transport than traditional ZnO nanoparticles. The resultant solar cell yielded an excellent performance with a solar power conversion efficiency of 4.24% under simulated one sun (AM1.5G, 100 mW cm(-2)) illumination.     

Co-sensitization of vertically aligned TiO2 nanotubes with two different sizes of CdSe quantum dots for broad spectrum

In order to absorb a broad spectrum in the visible region, vertically aligned TiO₂ nanotubes (TONTs) were co-sensitized by two different sizes of CdSe quantum dots (Q dots). The power conversion efficiency of co-sensitized Q dots solar cells showed 1.20%. The co-sensitization of Q dots showed higher performance than the single size sensitization. The incident photon-to-current conversion efficiency of co-sensitized TONTs electrode showed two absorption peaks at 520 and 550 nm demonstrating the sensitization of Q dots with two different sizes. This efficiency enhanced charge harvesting efficiency over the entire visible spectrum, particularly the 500–600 nm wavelength domains.     

High-voltage electrophoretic deposition for vertically aligned forests of one-dimensional nanoparticles

Deposition of aligned forests of 1D nanoparticles (carbon nanotubes and MnO(2) nanorods) on conductive, including flexible and transparent, substrates has been achieved at room temperature. The process, named high-voltage electrophoretic deposition (HVEPD), has been enabled by three key elements: high deposition voltage for alignment, low dispersion concentration of the nanoparticles to avoid aggregation, and simultaneous formation of a holding layer by electrodeposition. The effects of key parameters are investigated. The alignment on the vertical direction has been revealed by scanning electron microscopy of the samples, their superhydrophobicity, electrochemical performance, and capability to electrically connect two separated electrodes. Compared with their randomly oriented counterparts, the aligned nanoforests showed higher electrochemical capacitance, lower electrical resistance, and the capability to achieve superhydrophobicity, implicating their potential in a broad range of applications.     

Influence of highly efficient PbS counter electrode on photovoltaic performance of CdSe quantum dots-sensitized solar cells

PbS electrode with high catalytic activity to S_n ^2? reduction certificated by the measurements of electrochemical impedance spectroscopy and cyclic voltammetry was prepared by a simple method. The high catalytic activity makes it be a low-cost alternative counter electrode to platinum (Pt) to be used in quantum dots-sensitized solar cells (QDSSCs) based on polysulfide electrolyte. The photovoltaic performance enhancement of the quantum dots (QDs)-sensitized semiconductor thin films due to the PbS counter electrode was evaluated by fabricating QDSSCs based on CdSe QDs-sensitized ZnO (SnO₂) thin film. CdSe QDs-sensitized ZnO thin film has the lower internal total series resistance and electron transmission time, the higher electron lifetime and electron collection efficiency than the CdSe QDs-sensitized SnO₂ thin film. Replacing the Pt counter electrode with the PbS counter electrode leads to more improvement on the short circuit photocurrent density for QDSSC based on the ZnO thin film than the SnO₂ thin film. Therefore, the process to limit the photovoltaic performance of CdSe QDs-sensitized solar cell and the possible way to improve the photovoltaic performance were analyzed.     

Spectral broadening in quantum dots-sensitized photoelectrochemical solar cells based on CdSe and Mg-doped CdSe nanocrystals

In order to absorb a broad spectrum in visible region, a co-sensitized TiO₂ electrode was prepared by CdSe and Mg-doped CdSe quantum dots (Q dots). The power conversion efficiency of the co-sensitized Q dots photoelectrochemical solar cells (PECs) showed 1.03% under air mass 1.5 condition (I = 100 mW/cm²), which is higher than that of individual Q dots-sensitized PECs. The incident-photon-to-current conversion efficiency of the co-sensitized PECs showed absorption peaks at 541 and 578 nm corresponding to the two Q dots and displayed a broad spectral response over the entire visible spectrum in the 500–600 nm wavelength domains.     

Electrophoretic deposition of ZnO photoanode for plastic dye-sensitized solar cells

Plastic dye-sensitized solar cells have been fabricated based on an organic dye (D 149) and ZnO photoanode prepared via room temperature electrophoretic deposition (EPD) to yield a conversion efficiency of 4.17% under 100 mW cm^?2 AM 1.5 illumination. Intensity modulated photocurrent spectroscopy analyses reveal that the fabricated ZnO electrodes have adequate interparticle connection, even in the absence of any post-treatment. This study demonstrates that EPD is a convenient method for photoanode fabrication and ZnO photoelectrodes obtained via EPD are promising for efficient plastic solar cells.     

Structural characteristics of nanomaterials based on CdS quantum dots

CdS nanoparticles with sizes where a quantum-size effect is observed are structurally characterized in a detailed way. The following complex of structural methods is used to characterize the nanoparticles: electron diffraction; analytical, diffraction, and high-resolution transmission electron microscopy; and small-angle X-ray scattering.     

Low-temperature chemical bath deposition of crystalline ZnO

ZnO crystals can be grown from alkaline aqueous solution not only by the standard hydrothermal technique at temperatures between 350 °C and 400 °C, but also by chemical bath deposition (CBD) at temperatures below 100 °C. In the presence of ZnO and ScAlMgO₄ (SCAM) substrates almost all ZnO deposits on the substrate, with different habits, however. Under optimized conditions even homoepitaxial layers can be obtained, while rod-like structures are obtained on SCAM substrates. The chemistry and the driving forces behind the two processes are considered in detail and the temperature dependence of the solution composition has been calculated. The driving force for the ZnO crystal growth in the standard hydrothermal technique is the difference in the ZnO solubility in alkaline solutions at different temperatures. In contrast, the driving force for the chemical bath deposition of ZnO at low temperatures is the decay of zinc ion complex molecules with increasing temperature.