Synthesis and Computational Characterization of Organic UV-Dyes for Cosensitization of Transparent Dye-Sensitized Solar Cells

The fabrication of colorless and see-through dye-sensitized solar cells (DSCs) requires the photosensitizers to have little or no absorption in the visible light region of the solar spectrum. However, a trade-off between transparency and power conversion efficiency (PCE) has to be tackled, since most transparent DSCs are showing low PCE when compared to colorful and opaque DSCs. One strategy to increase PCE is applying two cosensitizers with selective conversion of the UV and NIR radiation, therefore, the non-visible part only is absorbed. In this study, we report synthesis of novel five UV-selective absorbers, based on diimide and Schiff bases incorporating carboxyl and pyridyl anchoring groups. A systematic computational investigation using density functional theory (DFT) and time-dependent DFT approaches was employed to evaluate their prospect of application in transparent DSCs. Experimental UV/Vis absorption spectra showed that all dyes exhibit an absorption band covering the mid/near-UV region of solar spectrum, with a bathochromic shift and a hyperchromic shifts for Py-1 dye. Computational results showed that the studied dyes satisfied the basic photophysical and energetics requirements of operating DSC as well as the stability and thermodynamical spontaneity of adsorption onto surface of TiO₂. However, results revealed outperformance of the thienothiophene core-containing Py-1 UV-dye, owing to its advantageous structural attributes, improved conjugation, intense emission, large Stokes shift and maximum charge transferred to the anchor. Chemical compatibility of Py-1 dye was then theoretically investigated as a potential cosensitizer of a reference VG20-C2 NIR-dye. By the judicious selection of pyridyl anchor-based UV-absorber (Py-1) and carboxyl anchor-based NIR-absorber (VG20), the advantage of the optical complementarity and selectivity of different TiO₂-adsorption-site (Lewis- and Bronsted-acidic) can be achieved. An improved overall PCE is estimated accordingly.     

Meso-Substituted Tetrabenzotriazaporphyrins for Dye-Sensitized Solar Cells

A novel tetrabenzotriazaporphyrin (TBTAP) bearing an anchoring carboxy-phenyl group at the meso-carbon position ( TT260 ) was synthesized by an efficient method, which involves the crossover condensation between phthalonitrile and aminoisoindoline precursors. Its optical and electrochemical properties were also investigated together with its use as sensitizer in dye-sensitized solar cells (DSSCs). The performance of TT260 was compared with a benchmark molecule TT1 , bearing similar bulky tert-butyl groups at the periphery. The device, which is the first ever example of meso-substituted TBTAP-based DSSC, exhibits a modest maximum power conversion efficiency of 2.4±0.1 % under one-sun conditions.     

Copper Complexes as Alternative Redox Mediators in Dye-Sensitized Solar Cells

Thirty years ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the sun’s energy and converting it into electricity. Since then, a lot of work has been dedicated to improving their global photovoltaic efficiency and their eco-sustainability. Recently, various articles showed the great potential of copper complexes as a convenient and cheap alternative to the traditional ruthenium dyes. In addition, copper complexes demonstrate that they can act as redox mediators for DSSCs, thus being an answer to the problems related to the I₃⁻/I⁻ redox couple. The aim of this review is to report on the most recent impact made by copper complexes as alternative redox mediators. The coverage, mainly from 2016 up to now, is not exhaustive, but allows us to understand the great role played by copper complexes in the design of eco-sustainable DSSCs.     

A Silicon-based Imidazolium Ionic Liquid Iodide Source for Dye-Sensitized Solar Cells

Room temperature molten salt 1‐methyl‐3‐(trimethylsilyl)methyl‐imidazolium iodide (MSII) was used for iodide sources in dye‐sensitized solar cells with an organic sensitizer 2‐cyano‐3‐[5‐[4‐[3‐[4‐(4‐(N,N‐bis(4‐methoxyphenyl)amino)phenyl)phenyl]‐2,5‐di‐n‐butyl‐pyrrolo[3,4‐c]pyrrole‐1,4‐dione]phenyl]furan‐2‐yl] acrylic acid (DPP‐I) as light harvester. With an optimized electrolyte (MSII:I₂:BI:GuNCS?24:2:2:0.4, BI and GuCNS are short for benzimidazole and guanidine thiocyanate, respectively), photovoltaic parameters (J_sc, V_oc, and ff) of device are 8.97 mA·cm^?2, 600 mV and 0.61, respectively, yielding a maximum overall photo‐to‐energy conversion ef?ciency (η) of 3.23%. And then the charge‐transfer mechanism of devices was deeply analyzed with electrochemical impedance spectroscopy (EIS) in the dark.     

有机染料D-SS和D-ST用于染料敏化太阳能电池光敏剂的比较

为了揭示D-SS和D-ST分子敏化的染料敏化太阳能电池(DSSCs)的物理机制,采用密度泛函理论(DFT)、含时密度泛函理论(TDDFT)和自然键轨道(NBO)分析,模拟计算染料D-SS和D-ST分子的结构、紫外-可见吸收光谱和能级结构.D-SS的紫外-可见吸收光谱相比于D-ST的有明显的红移,而且D-SS分子的摩尔吸光系数也高于D-ST分子的.D-SS分子本应该比D-ST分子拥有更高的俘获太阳辐射光子的能力,但由于D-SS分子的最高占据分子轨道(HOMO)能级位置比氧化还原电解质(|-/|-3)的氧化还原能级高,处于光激发态的D-SS分子向TiO2电极注入电子而被氧化后,不能顺利地从电解质中得到电子而还原,使得D-SS分子俘获光子的能力不能充分发挥,从而严重地降低了由其敏化的DSSCs的光电性能和光电能量转换效率.揭示了D-SS敏化的DSSCs的光电性能,特别是光电能量转换效率比D-ST敏化的DSSCs的低的原因.染料敏化剂分子的HOMO能级的位置对于DSSCs来说也是很重要的,用于DSSCs的有机敏化剂分子的HOMO能级的位置必须低于氧化还原电解质的氧化还原能级.     

锌卟啉自组装在染料敏化太阳能电池中的应用

制备了2种锌卟啉天线分子P2与P3,并通过自组装的方法成功地将这些天线分子应用到了染料敏化太阳能电池之中。与传统的D-π-A结构的染料相比,这种策略显示出了明显的优势：可以避免复杂的合成步骤,还可以通过调节天线分子和锚固基团的结构去改善染料的光子捕获能力并减少电荷复合行为。当4-吡啶-4-基苯甲酸（A）作为锚固基团时,经过分子自组装之后,基于A-P2的电池器件显示出了1.68%的转换效率,开路电压为526 mV,短路电流密度为5.39 mA·cm^-2,这充分说明了自组装策略在染料敏化太阳能电池中得到了很好的应用。而基于A-P3的电池器件能量转换效率只有0.79%,这可能主要是因为天线分子P3较大的位阻减小了染料吸附量的原因造成的。我们另外也测试比较了它们在光学、电化学、光伏性能等方面的差异。     

金属有机框架在染料敏化太阳能电池中的应用

为了获得高效率的染料敏化太阳能电池,其光阳极应该具有大的比表面积,以吸附足量的染料,获得很强的光捕获能力.从这个角度而言,将具有很大比表面积的金属有机框架材料引入到染料敏化太阳能电池的体系中,无疑是一种有益的探索.本文简介了金属有机框架材料在光伏领域的应用,并重点介绍了我们课题组在利用金属有机框架材料方面进行的一些探索,包括光阳极薄膜的处理、利用金属有机框架材料作为前驱体制备光阳极材料和光散射层.最后,本文对金属有机框架材料应用于染料敏化太阳能电池中的局限性及前景做了简要的展望.     

四硫富瓦烯作为染料敏化太阳能电池有机染料电子给体的理论研究

为了研究四硫富瓦烯(TTF)基团对有机染料敏化剂光电性能的影响,以咔唑染料Dye 1 为原型,引入TTF基团作为电子给体,设计了咔唑染料Dye 2. 采用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)分别计算模拟了纯染料分子和吸附团簇(TiO₂)₉后的形貌、分子轨道能级以及紫外-可见吸收光谱,采用周期性密度泛函理论计算模拟染料分子在二氧化钛(101)面吸附的表面形貌. 结果发现：在有机染料中引入TTF基团有助于有机染料敏化剂在二氧化钛表面的抗团聚作用和分子内的电荷转移;最为重要的是,TTF 基团的强给电子能力极大地增强了有机染料敏化剂的光捕获能力. 所有的计算结果表明,TTF基团是一种非常有潜力改善染料敏化剂光电性能的给电子基团.     

含中氮茚有机太阳能电池染料敏化剂的分子设计

采用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)方法研究了9个新的中氮茚[3, 4, 5-ab]异吲哚(INI)为给体的染料敏化剂性质.对影响电池效率的光捕获效率、电子注入、染料再生和电荷复合等重要因素与D5和D9染料进行了对比.计算表明,设计的INI系列敏化剂在440-500 nm内有最大吸收峰,表现出明显的电荷分离特征, INI2具有比D9染料更高的最大理论短路电流. Fukui反应指数计算指出INI2的亲核加成最易实现.染料分子在二氧化钛(101)面吸附计算表明,染料INI2以间接注入途径实现电子注入.综合计算结果,中氮茚INI染料有希望作为性能优良的染料敏化剂而得到应用.     

2,6-位取代的BODIPY染料敏化剂的合成及其性能

设计合成了3种新型基于氟化硼络合二吡咯甲川(BODIPY)衍生物的D-π-A型光敏染料CB1~3,其结构为:BODIPY核为桥联基团、N-苯基咔唑以不同位点连接BODIPY的2-位作为电子给体单元、氰乙酸连接于BODIPY的6-位作为电子受体单元。运用1H,13C NMR以及MALDI-TOF-MS对所合成的染料CB1-CB3进行了结构表征和确证。对3种染料CB1~CB3进行了UV-Vis和荧光等光物理特性、电化学行为、光伏性能研究,并通过DFT理论计算深入研究了其分子的几何结构与性能之间的关系。3种染料的吸收光谱主要位于420~600 nm 波段,LUMO能级在3.7 eV左右,HOMO能级在5.2 eV左右。N-苯基咔唑2-位与BODIPY相连的CB2,因更平整的分子结构和更为适合的共轭长度,具有更为优良的光谱吸收和分子内电荷迁移性能,因而表现出良好的光伏性能:在AM1.5(100 mW·cm^-2)的光强下,CB2敏化电池的开路电压(V_oc)为550 mV,电流密度(J_sc)为3.71 mA· cm^-2,填充因子(FF)为0.73,总光电转换效率(PCE)为1.49%。     

2,6-位取代的BODIPY染料敏化剂的合成及其性能

设计合成了3种新型基于氟化硼络合二吡咯甲川(BODIPY)衍生物的D-π-A型光敏染料CB1~CB3,其结构为:BODIPY核为桥联基团、N-苯基咔唑以不同位点连接BODIPY的2-位作为电子给体单元、氰乙酸连接于BODIPY的6-位作为电子受体单元。运用1H,13C NMR以及MALDI-TOF-MS对所合成的染料CB1~CB3进行了结构表征和确证。对3种染料CB1~CB3进行了UV-Vis和荧光等光物理特性、电化学行为、光伏性能研究,并通过DFT理论计算深入研究了其分子的几何结构与性能之间的关系。3种染料的吸收光谱主要位于420~600 nm波段,LUMO能级在3.7 eV左右,HOMO能级在5.2 eV左右。N-苯基咔唑2-位与BODIPY相连的CB2,因更平整的分子结构和更为适合的共轭长度,具有更为优良的光谱吸收和分子内电荷迁移性能,因而表现出良好的光伏性能:在AM1.5(100 m W·cm-2)的光强下,CB2敏化电池的开路电压(Voc)为550 m V,电流密度(Jsc)为3.71 m A·cm-2,填充因子(FF)为0.73,总光电转换效率(PCE)为1.49%。     

Adamantyl Side Chains as Anti-Aggregating Moieties in Dyes for Dye-Sensitized Solar Cells

Designing and evaluating novel dye concepts is crucial for the development of the field of dye-sensitized solar cells (DSSCs). In our recent report, the novel concept of tethering the anti-aggregation additive chenodeoxycholic acid (CDCA) to dyes for DSSC was introduced. Based on the performance improvements seen for this modification, the aim of this study is to see if a simplified anti-aggregation unit could achieve similar results. The following study reports the synthesis and photovoltaic characterization of two novel dyes decorated with the steric ethyladamantyl moiety on the π-spacer, and on the triarylamine donor. This modification is demonstrated to be successful in increasing the photovoltages in devices employing copper-based electrolytes compared to the non-modified reference dye. The best photovoltaic performance is achieved by a device prepared with the adamantyl decorated donor dye and CDCA, this device achieves a power conversion efficiency of 6.1 % (Short-circuit current=8.3 mA cm⁻², Open-circuit voltage=1054 mV, Fill factor=0.69). The improved photovoltaic performance seen for the adamantyl decorated donor demonstrate the potential of ethyladamantyl side chains as a tool to ensure surface protection of TiO₂.     

两种锌卟啉聚合物自组装染料敏化太阳能电池

合成了2种新型锌卟啉并与金属Mn构建配位聚合物(CPsx,x=1,2)。2种配位聚合物与锚定卟啉(ZnPA)通过金属-配体轴向配位自组装染料敏化太阳能电池(DSSC)。测试结果表明自组装电池具有较好的光电转换效率,特别是基于CPs2的装置具有较高的短路电流和转换效率。我们还对其光学、电化学及光电性能进行了研究,并通过透射电镜(TEM)对自组装体有效敏化在TiO_2电极上进行验证。     

二氢吲哚类染料用于染料敏化太阳能电池光敏剂的比较

采用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)对四种二氢吲哚染料进行研究, 从中筛选出相对优秀的染料敏化太阳能电池光敏剂. 对前线分子轨道的计算表明, 二氢吲哚染料的前线分子轨道结构非常有利于染料激发态向TiO2电极的电子注入. 对真空中的紫外和可见光吸收光谱的计算表明, 二氢吲哚染料的吸收光谱与太阳辐射光谱匹配较好. 对染料分子的能级计算表明, 二氢吲哚染料的能级结构比较适合于I-/I-3作电解液的TiO2纳米晶太阳能电池的光敏剂. 二氢吲哚染料最低未占据分子轨道(LUMO) 能级均比TiO2晶体导带边能级高, 能够保证激发态染料分子高效地向TiO2电极转移电子. 二氢吲哚染料最高占据分子轨道(HOMO)的能级比I-/I-3能级低, 保证了失去电子的染料分子能够顺利地从电解液中得到电子. 与实验数据比较, 得出在提高染料敏化太阳能电池转换效率方面, 对染料的关键要求是LUMO能级的位置. 染料分子的稳定性是染料敏化太阳能电池使用寿命的关键因素. 通过对化学键键长的比较表明, 二氢吲哚染料的分子稳定性基本相同. 对计算结果的分析表明, 二氢吲哚染料1(ID1)的LUMO能级最高, 分子稳定性最好, 在酒精溶液中的吸收光谱与太阳辐射光谱匹配很好, 在同类染料中是较好的染料敏化太阳能电池光敏剂.     

碳纳米管负载Ni2P作为染料敏化太阳能电池对电极的性能研究

本文以碳纳米管(CNTs)与Ni2P纳米晶制备CNTs-Ni2P复合材料,首次研究其染料敏化太阳能电池(DSSCs)的光阴极材料性能.使用X射线衍射(XRD)和透射电子显微镜(TEM)测定材料结构,观察材料形貌.结果表明,复合材料由碳纳米管和六方结构的磷化镍构成,无其它磷化物杂相,磷化镍纳米晶(约10 nm)分散于CNTs表面.交流阻抗(EIS)测试显示,与CNTs和Ni2P对电极相比,CNTs-Ni2P对电极的电荷转移电阻和扩散阻抗较低,接近Pt-FTO对电极水平.CNTs-Ni2P对电极的DSSCs光电流达12.9 mA·cm-2,能量转化效率达5.6%,接近Pt-FTO对电极的DSSCs能量转化效率(5.9%).这归因于高电催化活性的磷化镍纳米晶与高电导CNTs的协同效应.     

染料敏化太阳能电池掺杂TiO2纳晶光阳极

染料敏化太阳能电池（dye-sensitized solar cells, DSC）效率高、制作简单、成本低,因此被认为是最有希望的第三代太阳能电池。DSC光阳极的主要作用是吸附染料、传输电子和提供电解质扩散通道,因此对DSC光电性能具有决定性作用。近年来,通过掺杂调控TiO₂光阳极的电子特性,从而提高DSC的光电效率受到广泛关注。本文对掺杂TiO₂光阳极的研究现状进行了综述,重点分析了非金属元素、过渡金属元素及主族元素的掺杂对TiO₂光阳极的能带结构、光吸收特性、染料吸附量、电子传输和界面复合过程以及所组装DSC光电性能的影响,分析了非金属元素共掺杂的协同效应。同时,对稀土元素掺杂TiO₂作为光谱转换材料提高DSC光吸收效率和光电转换效率进行了探讨,最后论文对掺杂TiO₂光阳极今后的研究重点和研究方向进行了展望。     

一维纳米材料在染料敏化太阳电池中的应用*

一维纳米材料以无序或有序、单一或复合的形式被广泛应用于染料敏化太阳电池（dye-sensitized solar cells,DSSC）中,并展示其独特的电学和光学特性。基于一维纳米材料在DSSC中的应用而发展起来的“电子高速公路概念”越来越受到研究者的重视。本文综述了一维纳米材料在DSSC中的应用研究进展,重点介绍光阳极中一维纳米材料的电子学特性和合成方法、光阳极的制备特点、电池性能及其优缺点等,并就一维纳米材料在DSSC中的应用前景进行了展望。     

Self-Assembled Graphene/MWCNT Bilayers as Platinum-Free Counter Electrode in Dye-Sensitized Solar Cells

We describe the preparation and properties of bilayers of graphene- and multi-walled carbon nanotubes (MWCNTs) as an alternative to conventionally used platinum-based counter electrode for dye-sensitized solar cells (DSSC). The counter electrodes were prepared by a simple and easy-to-implement double self-assembly process. The preparation allows for controlling the surface roughness of electrode in a layer-by-layer deposition. Annealing under N₂ atmosphere improves the electrode's conductivity and the catalytic activity of graphene and MWCNTs to reduce the I₃⁻ species within the electrolyte of the DSSC. The performance of different counter-electrodes is compared for ZnO photoanode-based DSSCs. Bilayer electrodes show higher power conversion efficiencies than monolayer graphene electrodes or monolayer MWCNTs electrodes. The bilayer graphene (bottom)/MWCNTs (top) counter electrode-based DSSC exhibits a maximum power conversion efficiency of 4.1 % exceeding the efficiency of a reference DSSC with a thin film platinum counter electrode (efficiency of 3.4 %). In addition, the double self-assembled counter electrodes are mechanically stable, which enables their recycling for DSSCs fabrication without significant loss of the solar cell performance.     

Recent Advances on Pt-Free Electro-Catalysts for Dye-Sensitized Solar Cells

Since Prof. Grätzel and co-workers achieved breakthrough progress on dye-sensitized solar cells (DSSCs) in 1991, DSSCs have been extensively investigated and wildly developed as a potential renewable power source in the last two decades due to their low cost, low energy-intensive processing, and high roll-to-roll compatibility. During this period, the highest efficiency recorded for DSSC under ideal solar light (AM 1.5G, 100 mW cm⁻²) has increased from ~7% to ~14.3%. For the practical use of solar cells, the performance of photovoltaic devices in several conditions with weak light irradiation (e.g., indoor) or various light incident angles are also an important item. Accordingly, DSSCs exhibit high competitiveness in solar cell markets because their performances are less affected by the light intensity and are less sensitive to the light incident angle. However, the most used catalyst in the counter electrode (CE) of a typical DSSC is platinum (Pt), which is an expensive noble metal and is rare on earth. To further reduce the cost of the fabrication of DSSCs on the industrial scale, it is better to develop Pt-free electro-catalysts for the CEs of DSSCs, such as transition metallic compounds, conducting polymers, carbonaceous materials, and their composites. In this article, we will provide a short review on the Pt-free electro-catalyst CEs of DSSCs with superior cell compared to Pt CEs; additionally, those selected reports were published within the past 5 years.     

一种含氧供电基团的染料合成及其光伏性能

以对溴苯酚为原料,经碘丁烷的烷基化后,与硼酸三甲酯反应生成对丁氧基苯硼酸.环戊二噻吩经N-溴代丁二酰亚胺(NBS)的溴化和Vilsmeier-Haack反应,再与对丁氧基苯硼酸偶联、氰基乙酸缩合,生成目标化合物环戊二噻吩基光敏染料(L1).该化合物是一种以含氧基团为给体,环戊二噻吩作为共轭桥的有机染料,将其制备成有机染料敏化太阳能电池,在AM 1.5,100 mW/cm2的光强下,电池的单色光的光电转换效率(IPCE)值达到62%,开路电压(Voc)为535mV,短路电流密度(Jsc)为6.4mA·cm-2,填充因子(FF)为0.60,总光电转换效率为2.1%.