Fabrication of thin film nanocrystalline TiO2 solar cells using ruthenium complexes with carboxyl and sulfonyl groups

Two ruthenium complexes with carboxyl and sulfonyl groups have been synthesized, [Ru^II(L1)₂(NCS)₂] Ru^IIbis(4,7-diphenyl-1,10-phenanthroline-disulfonic acid disodium salt)-di(thiocyanate) [K313], [Ru^II(L1)₂(dcbpy)] Ru^II bis(4,7-diphenyl-1,10-phenanthroline-disulfonic acid disodium salt)(4,4′-dicarboxy-2,2′-bipyridyl) [K314] as photosensitizers. UV–vis, fluorescence emission, AFM and CV measurements are also supplied for ruthenium complexes. Photovoltaic properties of dye sensitized nanocrystalline semiconductor solar cells based on Ruthenium complexes which bear carboxyl and sunfonyl groups have been tested under standard AM 1.5 sunlight. Under the standard global AM 1.5 solar conditions, K314 and K313-sensitized solar cells demonstrate short circuit photocurrent densities of 14.92 mA/cm² and 11.23 mA/cm² and overall conversion efficiencies of 5.09% and 4.02%, respectively.     

N-Aryl stilbazolium dyes as sensitizers for solar cells

Eight new N-arylstilbazolium chromophores with electron donating -NR₂ (R = Me or Ph) substituents have been synthesized via Knoevenagel condensations and isolated as their PF₆⁻ salts. These compounds have been characterized by using various techniques including ¹H NMR and IR spectroscopies and electrospray mass spectrometry. UV-vis absorption spectra recorded in acetonitrile are dominated by intense, low energy π → π* intramolecular charge-transfer (ICT) bands, and replacing Me with Ph increases the ICT energies. Cyclic voltammetric studies show irreversible reduction processes, together with oxidation waves that are irreversible for R = Me, but reversible for R = Ph. Single crystal X-ray structures have been determined for three of the methyl ester-substituted stilbazolium salts and for the Cl⁻ salts of their picolinium precursors. Time-dependent density functional theory calculations afford reasonable predictions of ICT energies, but greater rigour is necessary for -NPh₂ derivatives. The four new acid-functionalized dyes give moderate sensitization efficiencies (ca. 0.2%) when using TiO₂-based photoanodes, with relatively higher values for R = Ph vs Me, while larger efficiencies (up to 0.8%) are achieved with ZnO substrates.     

染料敏化太阳能电池中的纳米TiO2多孔膜研究进展

介绍了染料敏化太阳能电池（DSSC）的工作原理;综述了应用于DSSC的纳米TiO2多孔膜制备方法以及掺杂改性方法。最后对用于DSSC的纳米TiO2多孔膜的发展方向进行了分析与展望。     

Synthesis of ruthenium complex and its application in dye-sensitized solar cells

An amphiphilic bipyridyl ligand, 4,4′-dicarboxy-octyl-2,2′-bipyridine, and its ruthenium(□) complex (termed as S8) were synthesized and characterized by UV/Vis, IR and NMR spectroscopy. The performance of this S8 complex as charge transfer photo-sensitizer in TiO₂-based dye-sensitized solar cells was studied under standard AM 1.5 sunlight and by using an electrolyte consisting of 0.70 M 1,2-dimethyl-3-propyl-imidazolium iodide, 0.10 M LiI, 40 mM iodine and 0.125 M 4-tert-butylpyridine in acetonitrile. Aliphatic chains linking to carboxylate groups of S8 act as an effective electron donor and carboxylate groups act as an effective electron withdrawing between the TiO₂ layer and the carboxylate linking TiO₂ layer leading to increasing of electron density at this interface, which is attributed to increasing efficiency of electron injection to the TiO₂ conduction band from the excited state of dye. The complex, S8, gave a photocurrent density of 13.02 mA/cm², 0.60 V open circuit voltage and 0.69 fill factor yielding 5.36% efficiency. The S8 dye with aliphatic chain improved conversion efficiency of the resulting DSSCs compared with a cell fabricated using the N3 dye.     

用于敏化太阳能电池的二氧化钛光阳极材料

敏化太阳能电池是当前清洁能源领域的研究热点之一,有望成为第三代太阳能电池。二氧化钛作为敏化太阳能电池的光阳极材料之一被广泛研究。主要综述了近20 a来二氧化钛光阳极材料的结构进展,并从电子注入效率、电子传输和基底电荷收集效率方面评述了各种结构的应用特点。另外,描述了当代三明治状二氧化钛工作电极的超薄保形覆盖层、工作层和阻挡层。然后,重点介绍了用于电子传输工作层的二氧化钛一维纳米阵列的制备方法及特点。最后,展望了光阳极结构与合成方法的未来发展趋势。     

Synthesis of a new class of cyclometallated ruthenium(II) complexes and their application in dye-sensitized solar cells

We synthesized a new class of cyclometallated ruthenium(II) complexes, Ru(tctpy)(C^N)(NCS) (1, 2), where C^N is a bidentate cyclometallating ligand such as 2-phenylpyridinato or 2-(4-(2-phenylethynyl)phenyl)pyridinato. Although these complexes exist as stereoisomers, the microwave synthetic technique yielded only one isomer. These compounds act as light sensitizers and have excellent light-harvesting properties, especially in the near-IR region. Therefore, they can be used in dye-sensitized solar cells (DSCs). A DSC sensitized with 2 shows a 10% incident photon-to-current conversion efficiency at 900 nm.     

Preparations of TiO2 pastes and its application to light-scattering layer for dye-sensitized solar cells

Three different structures of TiO₂ electrodes of the dye-sensitized solar cell (DSSC) devices were fabricated with layers of nanoparticles and light-scattering particles, and their photovoltaic performances were investigated when the polymer electrolytes were used. Especially, 20-nm- and 123-nm-TiO₂ pastes were prepared by using sol–gel method, to use for light-scattering layer from the incident light. The best efficiency of 6.03% under AM 1.5 was attained with a multi-layer structure using 123-nm-TiO₂ layer for the light-scattering layer and 9-nm-TiO₂ layer for the dense layer.     

Rutile TiO2-modified multi-wall carbon nanotubes in TiO2 film electrodes for dye-sensitized solar cells

The beneficial influence of incorporation of acid-treated and rutile TiO₂ (r-TiO₂)-modified multi-wall carbon nanotubes (MWNTs) in TiO₂ films on photocurrent–voltage characteristics of dye-sensitized solar cells (DSSCs) was studied. Two different routes were adopted for the modification of acid-treated MWNTs (a-MWNTs) with r-TiO₂. The films and MWNTs were characterized by electron microscopy, energy dispersive X-ray spectroscopy, XRD and Raman spectroscopy. In the case of incorporation of a-MWNTs with r-TiO₂ modification, short-circuit photocurrent (J _sc) of the pertinent DSSC increased by 35% compared with that of a cell with bare TiO₂ film. The open-circuit voltage remained almost the same for all cases. The enhanced J _sc is explained by the increased surface area of the film, enhanced cluster formation of TiO₂ particles around a-MWNTs, and improved interconnectivity of TiO₂ particles in the presence of a-MWNTs.     

TiO2 micro-flowers composed of nanotubes and their application to dye-sensitized solar cells

TiO₂ micro-flowers were made to bloom on Ti foil by the anodic oxidation of Ti-protruding dots with a cylindrical shape. Arrays of the Ti-protruding dots were prepared by photolithography, which consisted of coating the photoresists, attaching a patterned mask, illuminating with UV light, etching the Ti surface by reactive ion etching (RIE), and stripping the photoresist on the Ti foil. The procedure for the blooming of the TiO₂ micro-flowers was analyzed by field emission scanning electron microscopy (FESEM) as the anodizing time was increased. Photoelectrodes of dye-sensitized solar cells (DSCs) were fabricated using TiO₂ micro-flowers. Bare TiO₂ nanotube arrays were used for reference samples. The short-circuit current (J_sc) and the power conversion efficiency of the DSCs based on the TiO₂ micro-flowers were 4.340 mA/cm² and 1.517%, respectively. These values of DSCs based on TiO₂ micro-flowers were higher than those of bare samples. The TiO₂ micro-flowers had a larger surface area for dye adsorption compared to bare TiO₂ nanotube arrays, resulting in improved J_sc characteristics. The structure of the TiO₂ micro-flowers allowed it to adsorb dyes very effectively, also demonstrating the potential to achieve higher power conversion efficiency levels for DSCs compared to a bare TiO₂ nanotube array structure and the conventional TiO₂ nanoparticle structure.     

An efficient light-harvesting ruthenium dye for solar cell application

A novel, heteroleptic ruthenium dye comprising a vinyl group between the carboxylate and bipyridine segments as well as extended π-conjugation of the ancillary ligand, employing alkyl-bithiophene, was synthesized. The dye displayed a remarkably high absorption coefficient of 2.51 × 10⁴ M⁻¹ cm⁻¹ (at 562 nm) for its metal-to-ligand charge transfer band. The photo-to-current conversion efficiency of the corresponding dye-sensitized solar cell was 9.12% under AM 1.5 (100 mW/cm²) irradiation. Furthermore, owing to both the very strong metal-to-ligand charge transfer band and the large number of dye molecules adsorbed on the TiO₂ electrode, the conversion efficiency of the dye-sensitized cell was >7.5% at a light intensity ≤198 mW cm⁻².     

N-Ion-implanted TiO2 photoanodes in quantum dot-sensitized solar cells

Hierarchical nanostructured titanium dioxide (TiO(2)) clumps were fabricated using electrostatic spray with subsequent nitrogen-ion doping by an ion-implantation technique for improvement of energy conversion efficiency for quantum dot-sensitized solar cells (QDSCs). CdSe quantum dots were directly assembled on the produced N-ion-implanted TiO(2) photoanodes by chemical bath deposition, and their photovoltaic performance was evaluated in a polysulfide electrolyte with a Pt counter electrode. We found that the photovoltaic performance of TiO(2) electrodes was improved by nearly 145% upon N-ion implantation. The efficiency improvement seems to be due to (1) the enhancement of electron transport through the TiO(2) layer by inter-particle necking of primary TiO(2) particles and (2) an increase in the recombination resistance at TiO(2)/QD/electrolyte interfaces by healing the surface states or managing the oxygen vacancies upon N-ion doping. Therefore, N-ion-doped photoanodes offer a viable pathway to develop more efficient QD or dye-sensitized solar cells.     

Open-ended TiO2 nanotubes formed by two-step anodization and their application in dye-sensitized solar cells

We demonstrate a simple method to fabricate open-ended TiO(2) nanotube (NT) based dye-sensitized solar cells (DSSCs), where the NTs are attached to either TiO(2) nanorods (NRs) grown on fluorine-doped tin oxide (FTO) or FTO directly by nanoparticles (NPs). A completely hole-through TiO(2) NT layer is fabricated via a two-step anodization with heat treatment immediately after the first anodization. DSSCs with the open-ended NTs show better photovoltaic performance than those with close-ended NTs, due to the enhanced charge transport in the open-ended structure. Under optimum conditions, DSSCs fabricated with the open-ended NT layer exhibit a short circuit current density (J(sc)) of 19.10 mA cm(-2), an open circuit voltage (V(oc)) of 0.68 V, a fill factor (FF) of 0.49, and a power conversion efficiency (eff) of 6.3%.     

A study of TiO2/carbon black composition as counter electrode materials for dye-sensitized solar cells

This study describes a systematic approach of TiO₂/carbon black nanoparticles with respect to the loading amount in order to optimize the catalytic ability of triiodide reduction for dye-sensitized solar cells. In particular, the cell using an optimized TiO₂ and carbon black electrode presents an energy conversion efficiency of 7.4% with a 5:1 ratio of a 40-nm TiO₂ to carbon black. Based on the electrochemical analysis, the charge-transfer resistance of the carbon counter electrode changed based on the carbon black powder content. Electrochemical impedance spectroscopy and cyclic voltammetry study show lower resistance compared to the Pt counter electrode. The obtained nanostructures and photo electrochemical study were characterized.     

A natural tomato slurry as a photosensitizer for dye-sensitized solar cells with TiO2/CuO composite thin films

We have studied the performance of dye-sensitized solar cells by employing natural dye “anthocyanins” extracted from the tomato slurry as a sensitizer for the TiO₂/CuO photoanode. The extracts were anchored on TiO₂/CuO films deposited on an ITO substrate which was used as a photoanode. The dye adsorbed TiO₂/CuO films electrode, the copper plate as a counter electrode, and iodolyte as an electrolyte were assembled into DSSCs. The conversion efficiency of the DSSCs was found to be 2.96% with a V_OC of 0.615 V, J_SC of 6.6 mA/cm², and an FF of 0.73. This work highlights the use of contribution of the tomato slurry as a natural sensitizer to enhance the efficiency of DSSCs.     

Improving the performance of dye-sensitized solar cells with TiO2/graphene/TiO2 sandwich structure

This study investigates the extent to which the TiO₂/graphene/TiO₂ sandwich structure improves the performance of dye-sensitized solar cells (DSSCs) over that of DSSCs with the traditional structure. Studies have demonstrated that the TiO₂/graphene/TiO₂ sandwich structure effectively enhances the open circuit voltage (V_oc), short-circuit current density (J_sc), and photoelectrical conversion efficiency (η) of DSSCs. The enhanced performance of DSSCs with the sandwich structure can be attributed to an increase in electron transport efficiency and in the absorption of light in the visible range. The DSSC with the sandwich structure in this study exhibited a V_oc of 0.6 V, a high J_sc of 11.22 mA cm^-2, a fill factor (FF) of 0.58, and a calculated η of 3.93%, which is 60% higher than that of a DSSC with the traditional structure.     

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.     

Unravelling the bottleneck of phosphonic acid anchoring groups aiming toward enhancing the stability and efficiency of mesoscopic solar cells

Novel near-infrared sensitizers with different anchoring groups aiming toward improved stability and efficiency of dye-sensitized solar cells were synthesized. Adsorption of these dyes on the mesoporous TiO₂ surface revealed the dye adsorption rate of –CH=CH–COOH (SQ-139)>–CH=C(CN)COOH (SQ-140)>–PO₃H₂ (SQ-143)>–CH=C(CN)PO₃H₂ (SQ-148)>–CH=C(CN)PO₃H–C₂H₅ (SQ-157)>–PO₃H–C₂H₅ (SQ-151)> –CH=CH–COOH(–PO₃H₂) (SQ-162). The binding strength of these dyes on mesoporous TiO₂ as investigated by dye desorption studies follows SQ-162>SQ-143>SQ-148>SQ-139≫SQ-157~SQ-151≫SQ-140 order. The acrylic acid anchoring group was demonstrated to be an optimum functional group owing to its fast dye adsorption rate and better binding strength on TiO₂ along with good photoconversion efficiency. Results of dye binding on TiO₂ surface demonstrated that SQ-162 bearing double anchoring groups of phosphonic and acrylic acid exhibited>550 times stronger binding as compared to dye SQ-140 having cyanoacrylic acid anchoring group. SQ-140 exhibited the best photovoltaic performance with photon harvesting mainly in the far-red to near-infrared wavelength region having short circuit current density, open-circuit voltage and fill factor of 14.28 mA·cm^–2, 0.64 V and 0.65, respectively, giving the power conversion efficiency of 5.95%. Thus, dye SQ-162 not only solved the problem of very poor efficiency of dye bearing only phosphonic acid while maintaining the extremely high binding strength opening the path for the design and development of novel near-infrared dyes with improved efficiency and stability by further increasing the π-conjugation.     

Microwave assisted CdSe quantum dot deposition on TiO2 films for dye-sensitized solar cells

CdSe quantum dot (QD ) sensitized TiO(2) films have been fabricated using a one-step microwave assisted chemical bath deposition (MACBD) technique and used as photoanodes for quantum dot sensitized solar cells. This technique allows direct and rapid deposition and a good contact between the CdSe and TiO(2) films. The photovoltaic performances of the cells with CdSe deposited at different times are investigated. The results show that cells based on MACBD deposited TiO(2)/CdSe electrodes achieve a maximum short circuit current density of 12.1 mA cm(-2) and a power conversion efficiency of 1.75% at one Sun (AM 1.5 G, 100 mW cm(-2)), which is comparable with those fabricated using conventional techniques.     

Fabrication of double layer photoelectrodes using hierarchical TiO2 nanospheres for dye-sensitized solar cells

Double layer photoelectrodes consisting of the TiO₂ nanoparticles (npTiO₂) with 30–40 nm in diameter and the TiO₂ nanospheres (nsTiO₂) with 100–200 nm as a bottom and a top layer, respectively, were fabricated for dye-sensitized solar cells (DSSCs) employing a polymer electrolyte. The nsTiO₂ with hierarchical pores were prepared via the combined process of atom transfer radical polymerization (ATRP) and a sol–gel. Use of nsTiO₂ resulted in the remarkable enhancement of cell performance due to light scattering and dye adsorption capability. The overall energy conversion efficiency (η) of 5.5% was achieved by the formation of npTiO₂–nsTiO₂ double layer photoelectrode, which was higher than those formed by npTiO₂ alone (4.6%) or nsTiO₂–nsTiO₂ double layer (4.4%). Electrochemical impedance spectra (EIS) analysis showed that the npTiO₂–nsTiO₂ double layer had lower electron transfer resistance and longer electron lifetime, leading to facilitation of reduced recombination and consequently improvement of cell performance.