A higher performance dye-sensitized solar cell based on the modified PMII/EMIMBF4 binary room temperature ionic liquid electrolyte

Additives and iodine（I₂） are used to modify the binary room temperature ionic liquid（RTIL） electrolyte to enhance the photovoltaic performance of dye-sensitized solar cells（DSSCs）. The short-circuit current density（JSC） of 17.89 m A/ cm2, open circuit voltage（VOC） of 0.71 V and fill factor（FF） of 0.50 are achieved in the optimal device. An average photoelectric conversion efficiency（PCE） of 6.35% is achieved by optimization, which is over two times larger than that of the parent device before optimization（2.06%）, while the maximum PCE can reach up to 6.63%.     

Novel development towards preparation of highly efficient ionic liquid based co-polymer electrolytes and its application in dye-sensitized solar cells

Ionic liquid polymer electrolytes (ILPE) were prepared with poly(1-vinylpyrrolidone-co-vinylacetate) P(VP-co-VAc) copolymer, tetrahexylammonium iodide (THAI) salt and 1-butyl-3-methylimidazolium iodide (BMII), a room temperature ionic liquid (RTIL). The ILPEs were characterized using electrochemical impedance spectroscopy (EIS) analysis, X-ray diffraction (XRD) studies, Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA). The highest ionic conductivity obtained was 1.05 × 10⁻³ S cm⁻¹ at room temperature in ILPE3 which is the sample incorporated with 80 wt% of BMII. FTIR analysis proved the formation of complexes in between the copolymer, salt and ionic liquid. XRD studies have shown that ILPE3 has the optimum amorphous nature. The ILPE based dye sensitized solar cell (DSSC) was assembled by sandwiching the ILPE in between the nanoporous TiO₂ working electrode and Pt-coated counter electrode and thus subjected to device photovoltaic characterization. The DSSC with ILPE3 as its electrolyte has shown the highest power conversion efficiency (η) with a value of 4.93% with short circuit current density (J_sc), open circuit voltage (V_oc) and fill factor (FF) of 12.37 mA cm⁻², 0.69 V and 0.58, respectively. Temperature dependence studies has been done on the DSSCs to understand effect of the cell temperature on the performances of the DSSCs. EIS studies of the DSSCs shows that the ILPE is having higher diffusion coefficient compared to the GPE.     

Significant improvement of photocurrent in dye-sensitized solar cells by incorporation thiophene into electrolyte as an inexpensive and efficient additive

For the first time, thiophene as an efficient additive is applied in electrolyte of dye-sensitized solar cells (DSSCs). In the cell based on 2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid (TPA) sensitizer, addition of 1 M thiophene to the electrolyte (instead of 4-tert-butylpyridine (TBP)) increases significantly photocurrent density (J_sc) from 4.62 to 7.80 mA cm⁻². Consequently, overall conversion efficiency (η) enhances from 2.17% to 3.18% with a 46% improvement. For DSSC based on 2-cyano-3-(2′-(5′,10′,15′,20′-tetraphenylporphyrinato zinc(II))yl)acrylic acid (Zn-1) with modified electrolyte, J_sc increases from 4.18 to 8.23 mA cm⁻² and η improves from 1.46% to 1.96% that shows an enhancement of 34% in η. Intensity modulated photocurrent spectroscopy (IMPS) indicates the faster electron transfer in the DSSC based on thiophene additive compared to the standard device. Also, the higher electron diffusion coefficient (D_n) of the DSSC with modified electrolyte shows the thiophene additive facilitates the electron transfer. Based on cyclic voltammetry (CV) and UV–vis data, thiophene forms a molecular complex with iodine molecule in the electrolyte solution that has a remarkable effect on the redox couple oxidation–reduction reactions which improves J_sc. A significant improvement in J_sc with a small decrease in V_oc and thereby an increase in η are observed from addition thiophene.     

Efficient gel-state dye-sensitized solar cells adopting polymer gel electrolyte based on poly(methyl methacrylate)

We report an effective method to fabricate gel-state dye-sensitized solar cells (DSSCs) based on the PMMA polymer gel electrolyte. In this approach, the liquid-state polymer electrolyte solution was prepared by simply mixing the traditional liquid-state electrolyte with the polymer gelator solution and was injected into the DSSC in its liquid state. The liquid-state polymer electrolyte was then converted to the gel state (i.e., in situ gelation) simply by evaporating a portion of solvents at elevated temperatures. With this approach, liquid electrolytes already well developed and optimized for DSSCs can be readily adopted. Filling in the liquid/solution state ensures effective penetration of the electrolyte into pores of TiO₂ nanoparticle electrodes for attaining good contact and interface properties. The in situ gelation by heating (solvent evaporation) much simplifies the process. The polymer gel electrolyte thus prepared exhibited high ion conductivity and diffusivity comparable to those of traditional liquid electrolytes. The gel-state DSSCs thus fabricated exhibited a high power-conversion efficiency of 8.03% and much improved stability compared to the traditional liquid DSSC.     

TiO_2光阳极染料敏化太阳能电池的研究进展

通过介绍染料敏化太阳能电池(dye-sensitized solar cells,简称DSSC)的研究背景,指出了DSSC的研究意义。从光阳极、染料敏化剂、电解质和对电极等基本构成要素方面综述了DSSC的研究现状,并展望了其未来的发展方向。     

Efficient dye-sensitized solar cells based on CNTs and Zr-doped TiO2 nanoparticles

The light scattering, harvesting and adsorption effects in dye-sensitized solar cells (DSSCs) are studied by preparation of coated carbon nanotubes (CNTs) with TiO₂ and Zr-doped TiO₂ nanoparticles in the forms of mono- and double-layer cells. X-ray diffraction (XRD) analysis reveals that the phase composition of Zr-doped TiO₂ electrode is a mixture of anatase and rutile phases with major rutile content, whereas it is the same mixture with major anatase content for coated CNTs with TiO₂. Furthermore, the average crystallite size of Zr-doped TiO₂ electrode is slightly decreased with Zr introduction. Field emission scanning electron microscope (FE-SEM) images show that the porosity of Zr-doped TiO₂ electrodes is higher than that of undoped electrode, enhancing dye adsorption. UV–visible spectroscopy analysis reveals that the absorption onset of Zr-doped TiO₂ electrodes is slightly shifted to longer wavelength (the red-shift) in comparison with that of undoped TiO₂ electrode. Moreover, the band gap energy of TiO₂ nanoparticles is decreased by Zr introduction, enhancing light absorption. It is found that electron injection of monolayer TiO₂ electrode is improved by introduction of 0.025 mol% Zr, resulted in enhancement of its power conversion efficiency (PCE) up to 6.81% compared with 6.17% for pure TiO₂ electrode. Moreover, electron transport and light scattering are enhanced by incorporation of 0.025 wt% coated CNTs with TiO₂ in the over-layer of double layer electrode. Therefore, double layer solar cell composed of 0.025 mol% Zr-doped TiO₂ nanoparticles as the under-layer and mixtures of these nanoparticles and 0.025 wt% coated CNTs with TiO₂ as the over-layer shows the highest PCE of 8.19%.     

Delaying the degradation caused by water of dye-sensitized solar cells

A pure water electrolyte was fabricated and tested in printable flexible dye sensitized solar cells. The outdoor performance in highly humid condition shows significant degradation caused by water, which was rectified by introducing hydrophilic silica nanoparticles thus successfully delaying the degradation by three-fold.     

A remarkable enhancement of efficiency by co-adsorption with CDCA on the bithiazole-based dye-sensitized solar cells

Three new organic dyes containing a 5,5′-bithiazole or 2,2′-bithiazole entity have been synthesized for dye-sensitized solar cell (DSSC) applications. The conversion efficiencies of DSSCs fabricated are moderate due to serious dye aggregation. Upon addition of CDCA co-adsorbents, the optimized cell efficiencies were improved by 43–86%. The best efficiency was 6.31%, which reached 86% of N719-based DSSC fabricated and measured under similar condition. The efficiency can be further improved to 6.45% by adding a near-IR absorbing dye as the co-sensitizer due to broadened IPCE spectrum.     

Recent progress of efficient flexible solar cells based on nanostructures

Flexible solar cells are important photovoltaics (PV) technologies due to the reduced processing temperature,less ma-terial consumption and mechanical flexibility,thus they have promising applications for portable devices and building-integ-rated applications.However,the efficient harvesting of photons is the core hindrance towards efficient,flexible PV.Light man-agement by nanostructures and nanomaterials has opened new pathways for sufficient solar energy harvesting.Nanostruc-tures on top surfaces provide an efficient pathway for the propagation of light.Aside from suppressing incident light reflection,micro-structured back-reflectors reduce transmission via multiple reflections.Nanostructures themselves can be the absorber lay-er.Photovoltaics based on high-crystallinity nanostructured light absorbers demonstrate enhanced power conversion effi-ciency (PCE) and excellent mechanical flexibility.To acquire a deep understanding of the impacts of nanostructures,herein,a concise overview of the recent development in the design and application of nanostructures and nanomaterials for photovolta-ics is summarized.     

In situ preparation of hierarchically structured dual-layer TiO2 films by E-spray method for efficient dye-sensitized solar cells

Hierarchically-structured mesoporous TiO₂ films are prepared by the electrospray (E-spray) method. The microstructures of TiO₂ films can be feasibly tuned as spheres or nanocrystalline-mixed spheres, rendering in situ preparation of TiO₂ dual-layer. With these dual-layer TiO₂ films as photoanode and N719 as sensitizer, the dye-sensitized solar cell achieves a power conversion efficiency (PCE) of 8.96%, which is among the best of N719 devices so far, and constituting up to 19% improvement relative to single-layer TiO₂ photoanode based devices. To disclose the mechanism for the improvement, corresponding samples are prepared and investigated by scanning electron microscopy, electrochemical impedance spectroscopy, diffuse reflectance spectra. It was found that the dual-layer photoanode can simultaneously incorporate high dye loading and low charge transfer resistance, leading to high short current density and thus high PCE. Different to other reported dual-layer photoanodes, which often need two or more preparing procedures, only one step is needed in this work. To our best knowledge, it is the first time to employ only one step to in situ prepare photoanodes with dual-layer structures, which greatly simplifies the experimental processes.     

Theoretical study on novel double donor-based dyes used in high efficient dye-sensitized solar cells: The application of TDDFT study to the electron injection process

The geometries and electronic structures of organic dye sensitizers, CCT1A, CCT2A, CCT3A, CCT1PA, and CCT2PA comprising double-donor groups, π-spacer, and acceptor group forming D–D–π–A system, were studied using DFT and TDDFT. The calculated results have shown that TDDFT calculation using a newly-designed functional which takes into long-range interaction, CAM-B3LYP, was reasonably capable of predicting the excitation energies and the absorption spectra of the molecules. The adsorption of these dyes on the TiO₂ anatase (1 0 1) surface and the electron injection mechanism were also investigated using a dye-(TiO₂)₃₈ cluster model, employing PBE and TD-CAM-B3LYP calculations, respectively. The adsorption energy (E_ads) of CCTnA (n = 1–3) was calculated to be ?15.26, ?18.93, and ?20.12 kcal/mol respectively, indicating strong adsorption of dye to a TiO₂ surface by carboxylate groups. These calculated results suggested that the CCT3A is a promising candidate for highly efficient DSSCs. It was shown that the electron injection mechanism occurs by direct charge-transfer transition in a dye-TiO₂ interacting system, resulted in the stronger electronic coupling strengths of the anchoring group of the dyes and the TiO₂ surface which corresponded to higher observed J_sc as expected in CCT3A dye. Through a combined theoretical and experimental investigation we have shown that the trend of charge-injection efficiency in dye-sensitized solar cells constituted from dyes is determined by the adsorption energy of dye-(TiO₂)₃₈ complexes.     

Vertically aligned Ni3Se2 arrays with dendritic-like structure as efficient counter electrode of dye-sensitized solar cells

Fabrication of low-cost counter electrodes with high electrocatalytic performance is one of the most important challenges for dye-sensitized solar cells. Vertically aligned Ni₃Se₂ arrays with dendritic-like structure have been synthesized by a simple solvothermal method in this paper. Due to direct electron transfer and more catalytic active sites, Ni₃Se₂ arrays can be used as counter electrodes of dye-sensitized solar cells. The dye-sensitized solar cell based on Ni₃Se₂ array counter electrode shows a high photovoltaic performance with a high photoelectrical conversion efficiency of 4.62%, which is comparable with that of the dye-sensitized solar cell based on platinum counter electrode. To understand the chemical catalysis toward I₃^- reduction and interfacial charge transfer, the Ni₃Se₂ array counter electrode has been quantitatively investigated by the electrochemical measurements. The results indicate that the Ni₃Se₂ array counter electrode exhibits good catalytic activity and direct electron transfer for the reduction of I₃^-. Our research work will provide insight into the design and fabrication of counter electrode materials with high electrocatalytic performance for dye-sensitized solar cells.     

Highly efficient all solid state dye-sensitized solar cells by the specific interaction of CuI with NCS groups II. Enhancement of the photovoltaic characteristics

Highly efficient all solid state dye-sensitized solar cells (DSSC) were fabricated by the specific interaction of CuI with the NCS groups of the dye molecules and that of the counter electrodes. The counter electrodes were prepared by blending nano size carbon in the PEDOT:PSS dispersion. The counter electrodes were covered with the solution containing guanidine thiocyanate, and heated to give the electrode with larger number of NCS groups. Electrostatic adsorption between PEDOT:PSS and guanidine was investigated by X-ray photoelectron spectroscopy (XPS). DSSC were prepared by connecting the NCS groups of the dye molecule with those of the counter electrode with large surface area. The performances of the resulting DSSC were improved dramatically by the increase of the NCS groups on the counter electrode. It is noteworthy that the performances of the cell were higher than that of the cells prepared by the conventional liquid electrolyte. The highly efficient all solid state DSSC are manufactured with inexpensive and low quality materials, and the practical use is promising.     

TiO2基染料敏化太阳能电池的表面修饰及性能研究

采用水热法制备TiO₂浆料,用La(NO₃)₃溶 液浸泡TiO₂薄膜获得修饰电极。用X射线光电子能谱(XPS) 和扫描电子显微镜(SEM)对修饰电极的主要成分及形貌进行表征的结果显示,电极薄膜分为 上下两层,表 面包覆层粒径较大,为La₂O₃颗粒;下层颗粒粒径较小,为TiO₂颗粒。电流-电压测 试结果显示,与修饰 前相比,用La(NO₃)₃溶液浸泡30min获得的膜电极性能最优,使 开路电压和短路电流分别提高了6.8%和 18.5%。电化学阻抗谱(EIS)测试结果表明,相同偏压下,TiO₂/La ₂O₃电极界面复合电阻比TiO₂要大,说明 La₂O₃包覆层在一定程度上抑制了界面的电子复合,改善了电池的光电化学性能。     

一种基于光子晶体的高效太阳能电池反射器的设计

利用SiO2和TiO2介质,设计了一种可用于太阳能电池反射器的一维光子晶体。采用传输矩阵法对该光子晶体从可见光至近红外波长范围的反射谱进行了模拟计算,并分别讨论了周期数和入射角不同时反射谱的变化。结果表明:光线垂直入射时,周期数N增加,其反射谱在短波段的禁带数增加、禁带宽度变窄,而长波段的反射率增加。入射角θ增大时,平均反射率增加,因而该光子晶体具有良好的角度宽容性,可作为高效的太阳能电池率反射器。     

Synthesis and characterization of dianchoring organic dyes containing 2,7-diaminofluorene donors as efficient sensitizers for dye-sensitized solar cells

New metal free dianchoring organic dyes featuring A–π–D–π–D–π–A (acceptor – π bridge – donor – π bridge – donor – π bridge – acceptor) configuration have been designed incorporating fluorene and oligothiophene units and successfully synthesized. Elongating the conjugation pathway between the donor and acceptor units altered the distance between the anchoring sites besides the absorption and redox properties. These dyes exhibited broad and intense absorption when compared to the corresponding monoanchoring donor–π–acceptor congeners. Though the dye containing bithiophene unit exhibited comparatively low V_oc due to low electron life time and facile back electron transfer, showed high power conversion efficiency arising from the good light-harvesting capability attributable to the intense absorption peak in the visible region and enhanced interfacial electron transfer rate. This work demonstrates that the smaller distance of separation between the anchoring units increases the insulating capacity of the molecular layer which retards the back electron transfer.     

TiO2 nanotubes as flexible photoanode for back-illuminated dye-sensitized solar cells with hemi-squaraine organic dye and iodine-free transparent electrolyte

Back-illuminated Dye-Sensitized Solar Cells (DSSCs) have been fabricated employing TiO₂ nanotube (NT) arrays grown on a flexible Ti foil as a working electrode, an organic hemi-squaraine-based dye (CT1) as sensitizer, and a iodine-free transparent redox mediator (both in liquid and quasi-solid configuration) as electrolyte. The structural and morphological properties of the photoanodes and the obtained electrical performances on the final DSSC devices reaching conversion efficiencies values up to 2% are presented and discussed. The feasibility of a back-illuminated solar cell without corrosive and light-absorbing iodine-based electrolytes, metal-laden sensitizers and nanoparticles-based anodes has been demonstrated. Our work opens the way toward low-cost, non-polluting and flexible cells, proposing for the first time a solution for overcoming the limit of a low light harvesting in back-illuminated DSSCs.     

钛硅氧化物修饰对染料敏化太阳能电池性能影响研究

用溶胶-凝胶法配制了Ti-Si溶胶,并利用浸泡和煅烧法对染料敏化太阳能电池TiO2多孔光阳极进行了修饰处理,研究了Ti-Si氧化物修饰中Si含量对光阳极染料吸附量、TiO2/染料/电解质界面电荷传输电阻、电子寿命和光电转化性能的影响。发现Ti-Si氧化物修饰钝化了光阳极的表面态,改善了电极的电子寿命,促进了电荷的有效传输,提高了光生电子向TiO2中的注入效率;当Si含量为摩尔分数10%时,电池获得最高的光电转化效率7.11%。     

Efficient flexible dye-sensitized solar cells from rear illumination based on different morphologies of titanium dioxide photoanode

The TiO₂ with nanoparticles(NPs),nanowires(NWs),nanorods(NRs) and nanotubes(NTs) structures were prepared by using a in-situ hydrothermal technique,and then proposed as a photoanode for flexible dye-sensitized solar cell(FDSSC).The influences of the morphology of TiO₂ on the photovoltaic performances of FDSSCs were investigated.Under rear illumination of 100 mW·cm^-2,the power conversion efficiencies of FDSSCs achieved 6.96%,7.36%,7.65%,and 7.83% with the TiO_...