Improved performance of silicon‐nanoparticle film‐coated dye‐sensitized solar cells

Silicon (Si) nanoparticles with average size of 13 nm and orange–red luminescence under UV absorption were synthesized using electrochemical etching of silicon wafers. A film of Si nanoparticles with thickness of 0.75 µm to 2.6 µm was coated on the glass (TiO₂ side) of a dye‐sensitized solar cell (DSSC). The cell exhibited nearly 9% enhancement in power conversion efficiency (η) at film thickness of ～2.4 µm under solar irradiation of 100 mW/cm² (AM 1.5) with improved fill factor and short‐circuit current density. This study revealed for the first time that the Si‐nanoparticle film converting UV into visible light and helping in homogeneous irradiation, can be utilized for improving the efficiency of the DSSCs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical synthesis of ZnO hexagonal thin nanodisks and dye‐sensitized solar cell performance

Well defined highly monodispersed single crystalline ZnO hexagonal thin nanodisks have been synthesized by a wet chemical route. Ethylenediaminetetraacetic acid is used as an organic ligand in the chemical synthesis. Ultraviolet near band edge emission is predominant over the defect level emission in these ZnO nanodisks. The ZnO nanodisks have an average diameter of 150 nm and thickness of 40 nm. A dye‐sensitized solar cell is fabricated using ZnO nanodisks by spray pyrolysis deposition and it exhibits an efficiency of 2.63% with the ruthenium sensitizer N719 dye. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

染料敏化纳米晶薄膜太阳电池

文章介绍了一种新型的太阳电池——染料敏化纳米晶薄膜太阳电池的基本工作原理、目前研究的重点和进展以及应用前景和存在的问题，文章指出，这种新型的太阳电池以其制作简单并且具有进一步提高效率和降低成本的潜在优势，可以成为非晶硅太阳电池的有力竞争者。     

Highly defined and ordered top‐openings in TiO2 nanotube arrays

We report a very simple and novel approach to produce anodic TiO₂ nanotube arrays with highly defined and ordered tube openings. It is based on carrying out anodization through a slowly soluble photoresist coating. This eliminates the formation of undesired initiation layers on the tube tops and protects them to a certain extent from etching by the electrolyte.

     

Optical properties of dye sensitized TiO2 nanowires from time‐dependent density functional theory

We present a computational study based on time‐dependent density functional theory of the optical absorption spectra of TiO₂ nanowires sensitized with organic dye molecules. We concentrate on catechol and squaraine dyes. For those molecules, we compute adsorption geometries and energies and investigate the optical properties of the combined dye– nanowire system. We find that although the molecules have qualitatively different optical spectra in the gas phase, both lead to an enhancement of the absorption in the visible frequency range when adsorbed on a nanowire.

     

Drop‐cast and dye‐sensitized ZnO nanorod‐based visible‐light photodetectors

We report the facile fabrication of metal–semiconductor–metal (MSM) photodetectors with dye‐sensitized ZnO nanorods (NRs) operating at wavelengths of ～405–638 nm by a simple drop casting method. The ZnO NRs were synthesized by the hydrothermal synthesis method at 75 °C. The droplet of ethanol solution containing ZnO NRs was dropped between two metal electrodes and dried at 65 °C, which allows the ZnO NRs to be adhered and contacted to both metal electrodes. When a violet light of 405 nm was illuminated into the MSM ZnO NRs‐based photodetector, the photocurrent gain was obtained as ～3.9 × 10³ at the applied bias voltage of 5 V. By increasing the bias voltage from 10 V to 15 V, the device exhibited good recovery performance with a largely reduced reset time from 85.68 s to 2.47 s and an increased on–off ratio from 17.9 to 77.4. To extend the photodetection range towards the long visible spectral region, the ZnO NRs were sensitized by the N719 dye and then drop‐cast. The dye‐sensitized ZnO NRs‐based photodetector also exhibited good photocurrent switching under 638 nm of light illumination. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Inverted polymer solar cells with employing of electrochemical-anodizing synthesized TiO_2 nanotubes

An inverted structure of polymer solar cells based on Poly(3-hexylthiophene)(P3HT):[6-6] Phenyl-(6) butyric acid methyl ester(PCBM) with using thin films of TiO_2 nanotubes and nanoparticles as an efficient cathode buffer layer is developed. A total of three cells employing TiO_2 thin films with different thickness values are fabricated. Two cells use layers of TiO_2 nanotubes prepared via self-organized electrochemical-anodizing leading to thickness values of 203 and 423.7 nm, while the other cell uses only a simple sol–gel synthesized TiO_2 thin film of nanoparticles with a thickness of 100 nm as electron transport layer. Experimental results demonstrate that TiO_2 nanotubes with these thickness values are inefficient as the power conversion efficiency of the cell using 100-nm TiO_2 thin film is 1.55%, which is more than the best power conversion efficiency of other cells. This can be a result of the weakness of the electrochemical anodizing method to grow nanotubes with lower thickness values. In fact as the TiO_2 nanotubes grow in length the series resistance(Rs) between the active polymer layer and electron transport layer increases, meanwhile the fill factor of cells falls dramatically which finally downgrades the power conversion efficiency of the cells as the fill factor falls.     

Fabrication of open‐ended TiO2 nanotube arrays by a simple two‐step anodization

We report a two‐step anodizing approach for the fabrication of large‐scale open‐ended TiO₂ nanotube arrays (TNAs) on a conductive Au layer. In this method, a deposited Ti/Au bilayer film is initially anodized under a high potential to form and shape the TNAs. A following low potential is then in situ applied at a suitable time to slowly eliminate the remaining barrier layer at the bottom of the TNAs without further treatment. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental observation of two‐layer TiO2 nanotube arrays prepared by stepping‐voltage anodization

Two‐layer TiO₂ nanotube arrays were produced by stepping down the anodic voltage during which three nanotube interface structures between the top layer and the second layer were observed by SEM. We detected a polygonal ring structure on the top surface of the second layer and offer direct evidence of the growth of this second tube layer both at the cell boundary and right beneath the bottom of the first tube layer. For these processes, a possible growth mechanism is presented. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

锐钛矿相TiO2纳米管的制备及其染料敏化太阳电池

以商用金红石相TiO₂粉末为原料,通过在碱性溶液中150℃水热48h的方法合成TiO₂纳米管.采用SEM,TEM,XRD分析手段对TiO₂纳米管的形貌和结构演变进行了表征.制成的TiO₂纳米管与TritonX-100,乙酰丙酮混合后,通过丝网印刷的方法涂敷到ITO导电玻璃衬底上,并且在450℃下烧结30min后得到可应用于染料敏化太阳电池的多孔光阳极.将此光阳极浸泡于N719染料敏化后,与镀铂对电极组装电池,两者之间灌 关键词： 2纳米管')" href="#">TiO₂纳米管 染料敏化太阳电池 水热法     

Hydrothermal synthesis of TiO2 nanocrystals in different basic pHs and their applications in dye sensitized solar cells

In this research TiO₂ nanocrystals with sizes about 11–70 nm were grown by hydrothermal method. The process was performed in basic autoclaving pH in the range of 8.0–12.0. The synthesized anatase phase TiO₂ nanocrystals were then applied in the phtoanode of the dye sensitized solar cells. It was shown that the final average size of the nanocrystals was larger when the growth was carried out in higher autoclaving pHs. The photoanodes made of TiO₂ nanocrystals prepared in the pHs of 8.0 and 9.0 represented low amounts of dye adsorption and light scattering. The performance of the corresponding dye sensitized solar cells was also not acceptable. Nevertheless, the energy conversion efficiency was better for the state of pH of 9.0. For the photoanodes made of TiO₂ nanocrystals prepared at autoclaving pH of 10.0, the dye adsorption and light scattering were quite higher. The photovoltaic characteristics of the best cell in this state were 15.25 mA/cm², 740 mV, 0.6 and 6.8% for the short-circuit current density, open-circuit voltage, fill factor and efficiency, respectively. The photoanodes composed of TiO₂ nanocrystals prepared in autoclaving pHs of 11.0 and 12.0 demonstrated lower amount of dye adsorption and higher light scattering. This was quite considerable for the state of pH of 12.0. The energy conversion efficiencies were consequently decreased compared to that of the pH of 10.0. The optimum situation was finally discussed based on the nanocrystals size and its influence on the sensitization and light harvesting efficiency.     

Ordered porous TiO2 films obtained by freezing and the application in dye sensitized solar cells

TiO₂ films with ordered porous structure were prepared by freezing. By simply freezing wet TiO₂ film on a cold copper plate, ice crystals could grow from bottom of film. Removing such ice crystals then led to ordered, micro-sized pores in the films. With assistance of scanning electron microscopy and N₂ adsorption–desorption isotherms, micro-structural properties of the films were studied. Coarsening behavior of ice crystals was analyzed based on evolvement of the micro-structure. It was found that, both larger film thickness and longer freezing time were beneficial for the formation of ordered porous structure, which was caused by enhanced ice crystals growth. The films were then used to fabricate photoanode of dye sensitized solar cells, of which the photo-to-electric power conversion efficiency was evaluated. It was observed that, solar cell made of ordered porous TiO₂ film came out with 13% larger photo-current density comparing to that made of conventional doctor blading method, which is due to the enhanced light scattering by the ordered porous structure.     

A facile approach for decorating quantum dots deep inside of anodically grown self‐organized TiO2 nanotubes

We demonstrate here a simple but very effective approach to decorate anodically grown TiO₂ nanotubes (NTs) uniformly with CdS and PbS quantum dots (QDs) deep inside the NT walls. This approach is based on SILAR (successive ionic layer adsorption and reaction) technique assisted with evacuation of the NTs. The basic idea of evacuation is to remove air pockets trapped inside the NTs so as to clear the passage for the penetration of QD precursors down the bottom of the NTs.

     

Micro‐photoluminescence spectroscopy on heavily‐doped layers of silicon solar cells

We report and explain the photoluminescence spectra emitted from silicon solar cells with heavily‐doped layers at the surface. A micro‐photoluminescence spectroscopy system is employed to investigate the total spectrum emitted from both the heavily‐doped layer and the silicon substrate with micron‐scale spatial resolution. The two regions of the device give rise to separate photoluminescence peaks, due to band‐gap narrowing effects in the highly‐doped layer. Two key parameters, the absorption depth of the excitation wavelength, and the sample temperature, are shown to be critical to reveal the separate signatures from the two regions. Finally, this technique is applied to locally diffused and laser‐doped regions on silicon solar cell pre‐cursors, demonstrating the potential value of this micron‐scale technique in studying and optimizing locally doped regions. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Application of TiO2 with different structures in solar cells

The application of TiO2-based devices is mainly dependent on their crystalline structure,morphology,size,and exposed facets.Two kinds of TiO2 with different structures,namely TiO2 pompons and TiO2 nanotubes,have been prepared by the hydrothermal method.TiO2 with different structures is characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),and Brunauer-Emmett-Teller(BET) surface area analysis.Solar cells based on poly(3-hexylthiophene)(P3HT) and TiO2 with different structures are fabricated.In the device ITO/TiO2/P3HT/Au,the P3HT is designed to act as the electron donor,and TiO2 pompons and TiO2 nanotubes act as the electron acceptor.The effects of the TiO2 structure on the performance of hybrid heterojunction solar cells are investigated.The device with TiO2 pompons has an open circuit voltage(Voc) of 0.51 V,a short circuit current(Jsc) of 0.21 mA/cm2,and a fill factor(FF) of 28.3%.Another device with TiO2 nanotubes has a V oc of 0.5 V,J sc of 0.27mA/cm2,and FF of 28.4%.The results indicate that the TiO2 nanotubes with a unidimensional structure have better carrier transport and light absorption properties than TiO 2 pompons.Consequently,the solar cell based on TiO2 nanotubes has a better performance.     

PbICl precursor solutions for all solid-state PbS quantum-dot sensitized TiO2 nanorod array solar cells using successive ionic layer adsorption and reaction method

In this work, PbICl precursor solution in N,N-dimethylformamide was successfully applied to deposit PbS quantum-dots on TiO₂ nanorod arrays by successive ionic layer adsorption and reaction method (SILAR). The influence of PbI₂, PbBr₂, PbICl precursor solution on the morphology, crystal size and optical absorption of PbS quantum-dots was investigated and the photovoltaic performance of the corresponding solid-state PbS quantum-dot sensitized TiO₂ nanorod array solar cells with spiro-OMeTAD was evaluated. The average crystal sizes of PbS quantum-dots were 9.0 nm of PbI₂, 8.6 nm of PbBr₂ and 8.4 nm of PbICl and the photoelectric conversion efficiency of the corresponding solar cells achieved 2.63%, 3.00%, 3.45%. The result revealed that PbICl precursor solution was superior to PbBr₂ and PbI₂.