High efficiency dye-sensitized solar cells exploiting sponge-like ZnO nanostructures (original) (raw)

ZnO Nanostructures for Dye-Sensitized Solar Cells

Advanced Materials, 2009

This Review focuses on recent developments in the use of ZnO nanostructures for dye-sensitized solar cell (DSC) applications. It is shown that carefully designed and fabricated nanostructured ZnO films are advantageous for use as a DSC photoelectrode as they offer larger surface areas than bulk film material, direct electron pathways, or effective light-scattering centers, and, when combined with TiO 2 , produce a core-shell structure that reduces the combination rate. The limitations of ZnO-based DSCs are also discussed and several possible methods are proposed so as to expand the knowledge of ZnO to TiO 2 , motivating further improvement in the power-conversion efficiency of DSCs.

Sponge-like Porous ZnO Photoanodes for Highly Efficient dye-sensitized Solar Cells

Acta Physica Polonica A, 2013

We propose a 3D branched ZnO nanostructure for the fabrication of highly ecient dye-sensitized solar cell photoanodes. A coral-shaped structured Zn layer was deposited by radio frequency magnetron sputtering at room temperature onto uorine-doped tin oxide/glass sheets and then thermally oxidized in ambient atmosphere, obtaining a high-density branched ZnO lm. The porous structure provides a large surface area, and, as a consequence, a high number of adsorption sites, and the size and spacing of the nanostructures (on the order of the exciton diusion length) are optimal for good electron collection eciency. The proposed synthesis technique is simple and scalable and the reproducibility of the growth results was tested. The crystalline phase of the lm was investigated, evidencing the complete oxidation and the formation of a pure wurtzite crystalline structure. ZnO-based solar harvesters were fabricated in a microuidic architecture, using conventional sensitizer and electrolyte. The dependence of the cell eciency on dye incubation time and lm thickness was studied with IV electrical characterization and electrochemical impedance spectroscopy. The obtained conversion eciency values, with a maximum value of 4.83%, conrm the highly promising properties of this material for the implementation in dye-sensitized solar cell photoanodes.

Influence of morphology on the performance of ZnO-based dye-sensitized solar cells

ZnO nanomaterials with different morphologies, obtained by a sonochemical synthesis method at pH values of 5.5, 8, 10 and 12, have been used as starting materials for the fabrication of dye-sensitized solar cells. The morphology of the nanomaterials and the texture of the films deposited using screen printing depend on the synthesis pH, and the various exposed surface facets interact in a different manner with the dye and electrolyte solutions. The best cell performance was obtained with the morphology that resulted from the synthesis at pH 10, where the {100} and {110} crystal forms are predominant, and where dye coverage was largest. Interestingly, the BET total surface area was lowest for this nanomaterial illustrating the importance of morphology. The influence of the synthesis pH was also evident in the energetics and recombination kinetics of the solar cells. For the ZnO material synthesized at pH 5.5, the band edges appear to be shifted to more negative potentials, which could have resulted in a larger open circuit potential based on thermodynamic considerations. However, the electron life time for the pH 5.5 ZnO material is significantly smaller than for the other three synthesis pH values, indicating that the recombination kinetics are significantly faster for these cells as well, resulting in a smaller open circuit potential based on kinetics arguments. The balance between these two effects determines the experimentally observed open circuit potential. Overall, the results indicate that the dependence of the dye adsorption characteristics on ZnO nanomaterial morphology and film texture are the dominating factors that determine the solar cell performance.

Solid-state dye-sensitized solar cells based on ZnO nanocrystals

Nanotechnology, 2010

We report on the development of solution-processed ZnO-based dye-sensitized solar cells. We fabricate mesoporous ZnO electrodes from sol-gel processed nanoparticles, which are subsequently sensitized with conventional ruthenium complexes and infiltrated with the solid-state hole transporter medium 2, 2', 7, 7'-tetrakis-(N, N-di-p-methoxyphenylamine)-9, 9'-spirobifluorene (spiro-OMeTAD). Starting from ZnO nanorods synthesized from solution, we investigate the porous ZnO film morphology using various precursor

Biomimetic ZnO for Dye-Sensitized Solar Cells

Nanomaterials, 2020

A research study on the application of biomimetic ZnO (from eggshell membranes) as photoanodes in dye-sensitized solar cells (DSSCs) is presented. Biomimetic ZnO powder was produced and characterized. Its surface area, crystallinity, and morphology were analyzed and compared to commercial ZnO. Then, solar cells with and without dye were assembled using both the biomimetic and commercial oxides. On the dye-less cell, the oxide assumes the role of the photon absorber, while in the dye-sensitized cells, the oxide’s major function is the separation of the electron-hole pair and conduction of the electric charges formed. The characterization of the oxides showed that the biomimetic synthesis produced ZnO with a larger surface area, smaller crystallite size, and larger light absorption, possibly due to crystalline defects. SEM analysis on biomimetic ZnO revealed a tubular microstructure formed by nanocrystals, instead of the commercial powder showing spherical particles.

Scientific Review Dye Sensitized Solar Cells Incorporated with Tio 2-ZnO Nanoparticles

2017

The escalated and savage consumption of conventional sources of energy are leading to forecasted energy and environmental crises [1]. Solar Energy emerged as feasible alternative to confront the major environmental problems that result from the uncontrolled use of fossil resource in energy generation because "More energy from sunlight strikes Earth in 1 hour than all of the energy consumed by humans in an entire year" [2]. In 1991, Professor Grätzel reported a new low cost chemical solar cell by the successful combination of nanostructured electrode and efficient charge injecting dye, known as Grätzel cell or dye-sensitized solar cell which falls under the third generation photovoltaic cells [3]. In dye sensitized solar cells (DSSCs), dye molecules adsorbed on the oxide play a role of ""antenna"" for photon capturing. For this reason, accompanying with the development of DSSCs, organic dyes have been intensively studied with a focus on increasing the extinction coefficient and extending the optical absorption spectrum [4-10]. However, a major problem confronting these cells is the low efficiency of conversion. In optimizing the device performance and stability of DSSC, several research efforts have been expended on manipulating the corresponding architecture involving inorganic and organic systems as well as various interfaces so as to enhance the cell performance [11-14]. In general, ZnO nanoparticles based DSSCs shows low photoelectrochemical performance as compared to commercial TiO 2 based DSSCs [15]. Some of the limiting factor for this is insufficient attachment of dyes with the nanoparticles, formation of aggregation between the nanoparticles up on film formation, low injection rate, low regeneration of electron, and formation of Zn 2+ /dye complex. The formation of Zn 2+ /dye complex can agglomerate which comes from dissolution of the nanostructured film to form a thick covering layer instead of a monolayer, and is therefore inactive for electron injection which also limit the cell performance. This study proposed simple design strategies for realizing how to improve photovoltaic properties of the cell by coating on top of a TiO 2 semiconductor a layer of ZnO with different thickness. The PV performance of the formed DSSCs were investigated systematically. The conversion efficiency was increased from 0.0030 % to 0.0064 % for DSSC with 2 SILAR cycles which produces the best performance.

Photochemical performance of ZnO nanostructures in dye sensitized solar cells

Solid State Sciences, 2015

In this work, the photoconversion efficiencies of ZnO having diverse microstructures and structural defects have been investigated. A conversion efficiency of 1.38% was achieved for the DSSCs fabricated with as prepared ZnO nanorods having minimum vacancy defects and a favourable one dimensional directional pathway for electron conduction. The DSSCs fabricated with ZnO nanoparticles exhibited relatively low conversion efficiency of 1.004% probably due to multiple trapping/detrapping phenomena within the grain boundaries and ZnO flowers though exhibited a high dye adsorption capability exhibited the lowest conversion efficiency of 0.59% due to a high concentration of structural defects. Based on the experimental evidences, we believe that the type of defects and their concentrations are more important than shape in controlling the overall performance of ZnO based DSSCs.

Effects of Na-doping on the efficiency of ZnO nanorods-based dye sensitized solar cells

Journal of Materials Science: Materials in Electronics, 2014

Na-doped ZnO nanorods (Zn 1-x Na x O: x = 0.0, 0.02, 0.04) were grown by a chemical bath deposition method on ZnO seeded FTO substrates. The influence of Na-doping on the efficiency of ZnO nanorods-based dye-sensitized solar cells (DSSCs) was investigated. Undoped and Na-doped ZnO nanorods were used as photo-anodes for the fabricated DSSCs. X-ray diffraction measurements exhibited that all the samples had a wurtzite structure of ZnO with a preferred orientation of (002) plane. Scanning electron microscopy images of the samples revealed that all the samples displayed hexagonal shaped nanorods. It was observed from optical measurements that the band gap energy gradually decreased from 3.29 to 3.21 eV for undoped and 4 at.% Na-doped ZnO nanorods, respectively. Photoluminescence spectrum for undoped ZnO showed three peaks located at 379, 422, and 585 nm corresponding to UV emission, zinc vacancy, and deep level emission (DLE) peaks, respectively. When ZnO nanorods were doped with 2 at.% Na, the intensity of UV peak increased whereas the intensity of DLE peak decreased. The maximum conversion efficiency of DSSCs was found to be 0.22 % with a J sc of 0.80 mA/cm 2 , V oc of 0.49 V, and fill factor of 0.523 as ZnO nanorods were doped with 2 at.% Na atoms.

Effect of a compact ZnO interlayer on the performance of ZnO-based dye-sensitized solar cells

Solar Energy Materials and Solar Cells

ZnO is a promising material for application in dye-sensitized solar cells, related to its attractive electrical properties and the facile preparation of nanomaterials, with excellent control over the structure and morphology. In this work ZnO-based dye-sensitized solar cells were prepared, and the effect of the presence of a compact ZnO interlayer between the transparent conducting oxide (TCO) electrode and the nanostructured, mesoporous ZnO film on the performance of the solar cell is reported. The compact interlayer was deposited using planar rf magnetron sputtering, and the ZnO nanomaterial was prepared by forced hydrolysis from zinc acetate in ethanol solution. The presence of the compact interlayer has a positive effect on the overall characteristics of the solar cell and decreases the recombination rate from the TCO substrate, resulting in a higher open circuit voltage under low light conditions. The best efficiency of non-optimized solar cells at 1 sun was 4.0%.

Hierarchically Assembled ZnO Nanocrystallites for High-Efficiency Dye-Sensitized Solar Cells

Angewandte Chemie International Edition, 2011

Photoelectrochemical cells are promising devices for cheap, environmentally compatible, and large-scale solar energy conversion as an alternative to conventional solid-state semiconductor solar cells. Among excitonic cells, dyesensitized cells (DSCs) exhibit the highest performance in terms of energy conversion efficiency and long term stability, despite the fact that the efficiency remains below 13 % because of the intrinsic limitation in charge transport. The structure of the photoelectrodes is crucial in determining the functional properties of the photoelectrochemical system. In particular, the photoanode consists of a mesoporous wideband-gap oxide semiconductor film with a high specific surface (typically a thousand times larger than the bulk counterpart). To date, the highest photoconversion efficiency (PCE) has been achieved with film consisting of 20 nm TiO 2 nanocrystallites sensitized by different dye molecules (11.1 % for N719 dye, over 10 % for "black dye", and 11.4 % for C101, ). In addition to TiO 2 , a series of other ntype metal oxide semiconductors can in principle be used in DSCs, such as ZnO, SnO 2 , and In 2 O 3 . Much attention has been recently devoted to ZnO owing to its higher electron mobility and similar electronic band structure with respect to TiO 2 . Various strategies have been addressed to enhance PCE in ZnO-based DSCs, which are mainly based on tailoring the geometrical and structural features of ZnO. A possible solution to reduce electron recombination could be the use of one-dimensional nanostructures that are able to provide a direct pathway for the rapid collection of photogenerated electrons. However, only low PCE has been achieved to date, mainly because of the reduced internal surface area of the nanostructures. Hybrid structures have also been tested to improve light collection, such as combination of nanoparticles and nanowires (maximum PCE = 4.2 %), or hierarchical nanowires (maximum PCE = 2.63 %). Another strategy to enhance PCE is application of hierarchical photoanodes composed of large aggregates of nanocrystallites, which can act as light scattering centers while maintaining a high specific surface area. The synthetic procedure of photoanode preparation is crucial to improve PCE: an optimized photoanode composed of just ZnO nanoparticles without any geometrical feature for light confinement or enhanced electron transport resulted in the highest value of PCE (6.58 %) for a ZnO-based DSC. Herein we present the fabrication and characterization of hierarchically structured ZnO-based photoanodes in DSCs to enhance the PCE. Our approach addresses specifically the following points: 1) High optical density of the sensitized layer, allowing complete light absorption in the spectral range of the dye; 2) high light scattering of the absorbing layer, enhancing the time spent by light inside the sensitized film and improving light absorption; and 3) inhibition of back electron transfer between the conducting layer at the anode and the electrolyte. The films are prepared by the simple, cheap, and large-area-scalable spray pyrolysis method. The films are composed of polydispersed ZnO aggregates consisting of nanosized crystallites while submicrometer-sized aggregates act as efficient light scattering centers and nanoparticles provide the mesoporous structure and the large specific surface area needed for high dye loading. Additionally, a ZnO compact layer is intentionally formed between the conducting substrate and the layer composed of polydispersed aggregates. Such a layer acts as an efficient blocking layer for electron back reaction between the conducting glass at the anode and the electrolyte, improving the functional properties of the cells. This is the main innovation with respect to the work of Cao and co-workers, leading to unprecedented PCE up to 7.5 %, which is larger than ZnO nanoparticles (6.58 %), hierarchically structured ZnO without a blocking layer (5.4 %), and hierarchically arranged ZnO nanowires (2.63 %). As a further benefit, our method is extremely fast (no more than 1.5 h for the complete processing of a photoanode, while typically 8 h or 10 to 14 h are required), enabling its technological implementation.