ZnO-based Dye-sensitized Solar Cells Research Articles

N-Heterotriangulene chromophores with 4-pyridyl anchors for dye-sensitized solar cells

A series of N-heterotriangulenes decorated with 4-pyridyl anchors were synthesized and their performance in n-type TiO2- and ZnO-based dye-sensitized solar cells investigated.

Efficiency Enhancement of Dye-Sensitized Solar Cells' Performance with ZnO Nanorods Grown by Low-Temperature Hydrothermal Reaction.

In this study, aligned zinc oxide (ZnO) nanorods (NRs) with various lengths (1.5–5 µm) were deposited on ZnO:Al (AZO)-coated glass substrates by using a solution phase deposition method; these NRs were prepared for application as working electrodes to increase the photovoltaic conversion efficiency of solar cells. The results were observed in detail by using X-ray diffraction, field-emission scanning electron microscopy, UV-visible spectrophotometry, electrochemical impedance spectroscopy, incident photo-to-current conversion efficiency, and solar simulation. The results indicated that when the lengths of the ZnO NRs increased, the adsorption of D-719 dyes through the ZnO NRs increased along with enhancing the short-circuit photocurrent and open-circuit voltage of the cell. An optimal power conversion efficiency of 0.64% was obtained in a dye-sensitized solar cell (DSSC) containing the ZnO NR with a length of 5 µm. The objective of this study was to facilitate the development of a ZnO-based DSSC.

Comparative Study on the Influence of TiO2 Precursors on ZnO-Based Dye-Sensitized Solar Cells

We report the rational surface engineering of ZnO photoanode films by strict control of the TiO2 precursors for the facile design of hybrid structures and dye-sensitized solar cells (DSSCs) with increased energy conversion efficiencies. The effects of typical Ti sources [i.e., tetrabutyl titanate (TBOT), titanium isopropoxide (TTIP), and titanium tetrachloride (TiCl4)] on the ZnO film morphology, charge transfer, and DSSC performance were investigated systematically. The testing results revealed that TBOT-treated ZnO film exhibited the highest power conversion efficiency (PCE) and short circuit current density (Jsc) of 4.92% and 12.49 mA/cm2, respectively, which were largely improved compared with those of TTIP- and TiCl4-treated ZnO films under the same conditions. The excellent performance of TBOT-treated ZnO is mainly ascribed to improved light harvesting and increased charge-recombination resistance. Therefore, TBOT can be considered as a promising alternative for constructing TiO2/ZnO hybrid structur...

Performance analysis of electrophorically deposited ZnO-based dye-sensitized solar cells prepared using compression at elevated temperature along with postannealing

In this investigation, zinc oxide (ZnO)-based dye-sensitized solar cells (DSSCs) were fabricated by electrophoretic deposition (EPD) using fluorine-doped tin oxide (FTO)-coated glass substrates. Electrophoretically deposited photoanodes were annealed at different temperatures to investigate the effect of the postannealing temperature on the photovoltaic performance of DSSCs. Solar cells prepared with different compression pressures and compressions at an elevated temperature (optimum at 70 °C) were the state-of-the-art for this type of investigation. The photovoltaic performance was found to be improved by this novel heating and compression technique compared with the conventional postannealing or compression technique. When high-temperature postannealing (around 450 °C) was carried out along with heating and compression, the efficiency was found to be improved. From the surface morphology of the photoanodes investigated by scanning electron microscopy (SEM), it was evident that compression at an elevated temperature is favorable to obtain a uniform compact layer.

Enhanced Chemical Stability of ZnO Electrode for Dye-Sensitized Solar Cells with Ru Dyes Containing Limited Acidic Anchor Group

Two new Ruthenium-based dyes with carbazole groups (Ru-DiCz) or triphenyl amine groups (Ru-DiTPA) as donor moieties of a ligand were studied for ZnO-based dye-sensitized solar cells. Strong electron-rich donor moieties in both dyes induced a high molar extinction coefficient, thereby enhancing the overall power conversion efficiency through high JSC value. With limited acidic carboxyl anchor groups on the new Ru-dyes, the solar cells showed superior stability without aggregation of ZnO nanoparticles for a long-term immersion compared with a reference N3 sensitizer.

Cooperation of multifunction composite structures and fluorescein for photovoltaic performance-enhanced ZnO-based dye-sensitized solar cells

In this study, ZnO nanoparticles (NPs), ZnO nanorods (NRs) and ZnO nanosheet-based hierarchical structures (NSHSs) were rapidly synthesized using three simple approaches at relatively low temperatures and without any organic surfactants. Based on their structural advantages in light absorption, reflection and electron transfer, an NP/NSHS/NR hybrid structure was fabricated and used as a photoanode in dye-sensitized solar cells (DSSCs). The photoanode was treated in fluorescein acetonitrile solution (down-conversion materials) to enhance the photovoltaic efficiency, as well as in ascorbic acid ethanol solution to inhibit fluorescence quenching, which is caused by the I3−/I− electrolyte. Results showed that the NP/NSHS/NR hybrid structure plus fluorescein treatment was highly effective in improving the light harvesting capacity via an efficient electron transfer path and a down-conversion luminescence process, and the light-to-electric energy conversion efficiency of the DSSCs reached 6.54%, which increased by 34% compared with that of the ZnO NP-based DSSCs.

Influence of Structural Properties on the Performance of Dye-Sensitized Solar Cells Based on Electrodeposited ZnO

ZnO is an interesting material for application in the dye-sensitized solar cell (DCS) related to the large variety of low-temperature synthesis methods that allow for easy manipulation of the morphology and texture of the material. In particular, electrodeposition of crystalline ZnO can be achieved at room temperature, making it an excellent method for the preparation of solar cells based on flexible plastic substrates. We will present results on the performance of dye-sensitized solar cells based on electrodeposited ZnO, describing the electrodeposition method in detail, and compare the results to ZnO-based solar cells prepared using sol-gel synthesis and CVD. The morphology and texture are expected to influence the performance of the dye solar cell via a variety of effects. For instance, the exposed crystal facets may affect the dye bonding, dye coverage, and injection efficiency, the electron transfer kinetics to the solution, and the trap state distribution [1]. Using these materials, we have compared the electron transport and recombination properties using small-signal perturbation techniques [2]. We have also addressed the influence of solution additives on the performance of ZnO-based dye-sensitized solar cells and rationalized the results. The influence of surface facet exposure on dye bonding is highlighted.

Dependence of ZnO-based dye-sensitized solar cell characteristics on the layer deposition method

The selection of a proper method for the semiconductor layer deposition is an important requirement towards a high efficiency for dye-sensitized solar cells (DSSCs). We compared three techniques for deposition of the semiconductor thin layer in ZnO-based DSSCs, in order to determine the dependence between the deposition method, the ZnO film properties and finally the DSSCs characteristics. For this purpose, we varied the method used for deposition of the semiconductor film and we replaced ZnO with Al-doped ZnO. The nanostructured films morphology was analysed by transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction. The optical properties were examined by UV–visible spectroscopy and the bandgap energies were calculated using the Tauc equation. The higher fill factor value was registered for DSSCs based on the ZnO film obtained by electrochemical method, but the higher efficiency was registered for doctor-blading method.

Ruthenium polypyridyl TG6 dye for the sensitization of nanoparticle and nanocrystallite spherical aggregate photoelectrodes.

A ruthenium polypyridyl dye containing a hexasulfanyl-styryl modified bipyridyl group as ancillary ligand, coded TG6, is investigated as a sensitizer for ZnO-based dye-sensitized solar cells (DSSCs). The advantages of this dye are a broad wavelength absorption spectrum, a large loading in ZnO photoelectrodes, a significantly larger extinction coefficient compared to more classical Ru-polypyridyl dyes, and the formation of less agglomerate in the pores of the ZnO layers. TG6 has been used to sensitize ZnO nanorod particle layers of high structural quality and ZnO layers made of submicrometer spheres composed of aggregated nanocrystallites and that develop an internal surface area. The latter are highly light-scattering in the visible wavelength region but more difficult to sensitize correctly. The TG6 dye has been compared with the metal-free D149 dye and has been shown more efficient for photoconversion. The best performances have been obtained by combining TG6 with the nanorod layer, the optimal power conversion efficiency being measured at 5.30% in that case. The cells have been investigated by impedance spectroscopy over a large applied voltage range. We especially show that the submicrometer sphere layers exhibit lower conductivity and lower charge collection efficiency as compared to the nanorod particle ones.

A composite catalyst of reduced black TiO2-x/CNT: a highly efficient counter electrode for ZnO-based dye-sensitized solar cells.

A composite catalyst (reduced black TiO2-x/carbon nanotube) was synthesized through a simple sol-gel method and applied as a counter electrode (CE) in ZnO-based dye-sensitized solar cells (DSSCs). This material demonstrated notable electrocatalytic activity for I3(-) reduction, and the resultant DSSCs achieved a PCE of 5.71%.

Preparation and characterization of ZnO/graphene nanocomposite for improved photovoltaic performance

Zinc oxide (ZnO) nanoparticles and ZnO/graphene (ZG) nanocomposite were synthesized via simple chemical route and its application as a photoanode for dye-sensitized solar cell (DSSC) was demonstrated. The prepared ZnO and ZG were structurally characterized by X-ray diffraction and micro-Raman techniques. The scanning electron micrograph of ZG revealed the spherical-shaped ZnO nanoparticles of particle size ~160 nm was anchored on the two-dimensional graphene sheets. UV–Vis absorption spectroscopy showed that the ZG nanocomposite has enriched visible light absorption. The DSSCs were fabricated using the synthesized ZnO and ZG nanocomposite as photoanode and the effect of low-cost organic dyes on the photovoltaic performances of the solar cells were investigated. Comprehensive performances of ZG are better than that of ZnO-based DSSCs. The ZG DSSCs show power conversion efficiency (PCE) of 1.5 and 0.98 % for RB and EY sensitized electrodes, respectively. Moreover, the ZG dominates in many aspects due to the presence of graphene.

Erratum to: Synthesis and fabrication of Mg-doped ZnO-based dye-sensitized solar cells

Erratum to: Synthesis and fabrication of Mg-doped ZnO-based dye-sensitized solar cells

Effect of blocking layer to boost photoconversion efficiency in ZnO dye-sensitized solar cells.

The effect of a ZnO compact blocking layer (BL) in dye-sensitized solar cells (DSSCs) based on ZnO photoanodes is investigated. BL is generated through spray deposition onto fluorine-doped tin oxide (FTO) conducting glass before the deposition of a ZnO active layer. The functional properties of dye-sensitized solar cells (DSSCs) are then investigated as a function of the thickness of the BL for two different kinds of ZnO active layer, i.e., hierarchically self-assembled nanoparticles and microcubes composed of closely packed ZnO sheets. Presence of BL leads to the improvement of photoconversion efficiency (PCE), by physically insulating the electrolyte and the FTO. This effect increases at increasing BL thickness up to around 800 nm, while thicker BL results in reduced cell performance. Remarkable increase in Jsc is recorded, which doubles as compared to cells without blocking layer, leading to PCE as high as 5.6% in the best cell under one sun irradiation (AM 1.5 G, 100 mW cm(-2)). Electrochemical impedance spectroscopy (EIS) elucidates the mechanism boosting the functional features of the cells with BL, which relies with enhanced chemical capacitance together with an almost unchanged recombination resistance, which are reflected in an increased electron lifetime. The results foresee a straightforward way to significantly improve the performance of ZnO-based DSSCs.

Influence of structural and chemical properties on electron transport in mesoporous ZnO-based dye-sensitized solar cell

Two chemical bath deposition (CBD) solutions were prepared at two different temperatures of 60 and 80 °C for dye-sensitized solar cell (DSSC) application. The deposition time was varied from 12, 18, and 24 h. The X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis confirmed a transformation of hydrozincite into ZnO after calcined at 300 °C. The flower-like structure was observed by scanning electron microscopy (SEM) analysis. The ZnO photoanode deposited at 80 °C for 24 h showed the highest incident photon to charge carrier efficiency (IPCE) value of 5.25 %. The power conversion efficiency, η increased from 1.81 to 2.45 % for the photoanode deposited at 60 and 80 °C, respectively. The effective electron lifetimes, τeff of 6.36 ms was measured as much shorter than the TiO2-based DSSC (τeff of 25 to 160 ms). The effective electron diffusion coefficient, Deff, increased from 1.7 × 10−3 to 4.7 × 10−3 cm2.s−1 when the deposition temperature increases from 60 to 80 °C. Effective rate constant for recombination, keff of 157 s−1 was calculated for both samples. The results and analysis of the film’s surface structure, morphology, electron diffusion, and recombination inside the mesoporous ZnO photoanode proved the applicability of ZnO for the DSSC’s application.

Improving scattering layer through mixture of nanoporous spheres and nanoparticles in ZnO-based dye-sensitized solar cells.

A scattering layer is utilized by mixing nanoporous spheres and nanoparticles in ZnO-based dye-sensitized solar cells. Hundred-nanometer-sized ZnO spheres consisting of approximately 35-nm-sized nanoparticles provide not only effective light scattering but also a large surface area. Furthermore, ZnO nanoparticles are added to the scattering layer to facilitate charge transport and increase the surface area as filling up large voids. The mixed scattering layer of nanoparticles and nanoporous spheres on top of the nanoparticle-based electrode (bilayer geometry) improves solar cell efficiency by enhancing both the short-circuit current (Jsc) and fill factor (FF), compared to the layer consisting of only nanoparticles or nanoporous spheres.

Efficiency enhancement of ZnO-based dye-sensitized solar cell by hollow TiO2 nanofibers

One-dimensional nanostructures as the photoanode of dye-sensitized solar cell (DSSC) can provide a direct transport pathway for electrons injection to increase electrons transfer efficiency. In this work, hollow TiO2 nanofibers were fabricated by one step electrospinning based on sol–gel method, and were used to successfully enhance the conversion efficiency of ZnO-based DSSC. The effects of different TiO2 weight percentages on the performance of TiO2/ZnO composite photoanode were investigated systematically. The results indicate that the light scattering of the photoanode film is increased and the electrons recombination is suppressed when appropriate amount of hollow TiO2 nanofibers was added into ZnO. The maximal energy conversion efficiency reaches 4.59% by adding 10wt.% of hollow TiO2 nanofibers, which is 62% higher than that of DSSC based on pure ZnO nanoparticles.

Improved dye-sensitized solar cell with a ZnO nanotree photoanode by hydrothermal method.

This study investigated the influence of ZnO nanostructures on dye adsorption to increase the photovoltaic conversion efficiency of solar cells. ZnO nanostructures were grown in both tree-like and nanorod (NR) arrays on an AZO/FTO film structure by using a hydrothermal method. The results were observed in detail using X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), UV-visible spectrophotometry, electrochemical impedance spectroscopy, and solar simulation. The selective growth of tree-like ZnO was found to exhibit higher dye adsorption loading and conversion efficiency than ZnO NRs. The multiple ‘branches’ of ‘tree-like nanostructures’ increases the surface area for higher light harvesting and dye loading while reducing charge recombination. These improvements result in a 15% enhancement in power conversion. The objective of this study is to facilitate the development of a ZnO-based dye-sensitized solar cell.

Application of ZnO micro-flowers as scattering layer for ZnO-based dye-sensitized solar cells with enhanced conversion efficiency

ZnO micro-flowers were synthesized by a simple solution deposition method without the need of seed or keeping fresh deposition solution. The synthesized ZnO micro-flowers were used as scattering layer for dye-sensitized solar cells (DSSCs) fabricated with ZnO nanoparticles photoanode. The UV–vis diffused reflectance absorption spectra (DRS), electrochemical impedance spectroscopy (EIS) and photoinduced open-circuit voltage decay (OCVD) measurements show that the ZnO micro-flowers/nanoparticles bilayer film-based solar cell has much higher light harvesting efficiency, lower resistance and longer electron lifetimes as compared with the ZnO nanoparticles film-based one, and consequently resulting in an improved conversion efficiency due to the scattering effect of ZnO micro-flowers layer. The simple methods of the fabrication of both the ZnO micro-flowers and the ZnO bilayer film-based solar cell, which was fabricated with photoanode consisting of ZnO nanoparticles as underlayer and ZnO micro-flowers as overlayer, are promising for the development of the low-cost, eco-friendly, and durable devices with high light-to-electricity conversion efficiency.

Multi-functional energy conversion and storage electrodes using flower-like Zinc oxide nanostructures

In the present paper we demonstrate the efficient use of shape controlled flower-like ZnO (Zinc oxide) nanostructured particles as multifunctional electrode for both energy conversion and storage applications, i.e. Dye-sensitized Solar Cells (DSCs) and lithium-ion batteries.As regards DSC (Dye-sensitized Solar Cell) device, ZnO flower-like particles, prepared by a simple, low-cost and reliable hydrothermal method under mild reaction temperature, are efficiently used as photoanode in a microfluidic architectured cell in combination with NMBI (N-methylbenzimidazole), employed as additive of the electrolytic solution for the first time in a ZnO-based DSC. We obtain a remarkable sunlight conversion efficiency of 3.6%.As regards storage applications, a stable long-term ambient temperature cycling behavior in lithium cell is demonstrated, even at increasingly higher currents. Remarkable charge-discharge efficiency and specific capacity are obtained up to 200 cycles, which is the highest number of cycles reported so far for similar systems. Noteworthy, such results are achieved without the addition of foreign additives, nor during the synthesis process neither during the electrode preparation, and also no carbon coating on ZnO surface is used.The originality of the present paper consists not only in showing for the first time the efficient operation of such ZnO particles as anode in Li-ion batteries for prolonged cycling, but also in demonstrating the versatile and multifunctional use of the same material for two different energy related applications. The reported results enlighten indeed the promising prospects of the flower-like ZnO nanostructured material for the successful implementation as stable and long-term performing anodic material in the next generation of both energy conversion and storage devices.

Photovoltaic properties of ZnO photoanode incorporating with CNTs for dye-sensitized solar cell application

Zinc oxide carbon nanotube (ZnO-CNTs) thin films were prepared by a chemical bath deposition (CBD) method and immersed in N719 dye for 24 h. The structure and surface morphology of the samples was captured by X-ray diffraction (XRD) and field effect scanning electron microscopy (FESEM) unit, respectively. The photovoltaic properties of ZnO- and ZnO-CNT-based dye-sensitized solar cells (DSSCs) were measured by considering the power conversion efficiency (η), photocurrent density (J sc), open-circuit voltage (V oc), and fill factor (FF). The cell's efficiency doped with single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) reached 0.65 and 0.28 %, respectively. ZnO-based DSSC generated only η = 0.003 %. The electrochemical impedance spectroscopy (EIS) unit was employed to investigate the electron transport properties such as effective electron lifetime (τ eff), effective electron chemical diffusion coefficient (D eff), and effective electron diffusion length (L n ). The addition of CNTs has enhanced the photovoltaic properties of the DSSCs and reduced the recombination effect inside the solar cell.