【作者】 李晶；

【导师】 田禾；

【作者基本信息】 华东理工大学 ， 应用化学， 2011， 博士

【摘要】 染料敏化太阳能电池(DSCs)是利用吸附于半导体表面的染料分子来捕获太阳光并把太阳能转换成电能的一种新型太阳能电池,具有成本低廉、制作工艺简单、可制备大面积的柔性电池等优势而受到广泛关注。如何提高DSCs的光电转换效率和使用寿命是目前有机太阳能电池研究的两个关键问题。本论文从共吸附剂竞争吸附,在电解质中加入添加剂和优化半导体电极三个方面入手,对基于芳胺类敏化剂的器件性能进行了系统的研究和优化,提高了光电转换效率。同时研究了准固态电池的光电性能,与液态电池相比,提高了电池的稳定性,延长了电池的使用寿命。各章的主要内容和主要结论简述如下：第一章简要介绍染料敏化纳米晶太阳能电池的结构及工作原理,以及评价太阳能电池性能的参数。在此基础上,综述了目前染料敏化太阳能电池的研究进展和亟待解决的问题,提出了本论文的研究思路和内容。第二章介绍了染料敏化太阳能电池的制作过程和测试方法,重点介绍了几种不同的纳米尺度的TiO2胶体的制作方法,以及利用Doctor Blade和丝网印刷技术制备多孔膜电极的方法。第三章利用共吸附剂鹅去氧胆酸(CDCA),对两个含有吩噻嗪的有机染料(P1和P2)的光电性能进行了优化。研究了不同浓度的共吸附剂对两种染料的吸收光谱和光电性能的影响,结果表明共吸附剂有效地抑制了染料的π-π堆积,提高了电子的注入效率,进而提高短路电流。当CDCA浓度为10 mM时,染料P1和P2的光电转换效率达到最大值,分别为4.80%和5.31%,与未添加CDCA的两个染料的DSCs光电转换效率相比分别提升了33%和25%。同时交流阻抗数据显示,CDCA的加入,使染料的电子寿命也有所提升,这是开路电压显著提高的原因。第四章首次将含有亚氨基联芪和亚氨基二苄给体单元引入到有机太阳能电池染料敏化剂中,系统研究了四个亚氨基联芪类敏化染料M1-M4的光物理、电化学和光电转换效率。研究表明：增大共轭体系,吸收波长发生红移,摩尔消光系数增加,含有亚氨基联芪和噻吩乙烯的染料M2共轭体系最大,最大吸收波长最长,摩尔消光系数最大,有利于吸收更多的太阳光；同时M2具有最低的LUMO轨道能级,激发态电子注入到Ti02导带的效率最高。将四个染料与三苯胺类似物的光电性能进行了比较,亚氨基联芪类的敏化剂M1-M4显示出更好的光伏性能,说明亚氨基联芪衍生物是一类很好的电子给体。进一步比较发现,亚氨基联芪为电子给体的光敏染料(M2和M4)的光电性能优于含亚氨基二苄给体的染料(M1和M3)。针对有机敏化剂中普遍存在的聚集问题,我们采用了鹅去氧胆酸抑制吸附,改变电解质中4-叔丁基吡啶(TBP)的浓度和不同溶剂(二氯甲烷、乙醇、异丙醇、叔丁醇、甲苯、甲醇和四氢呋喃等)染浴三条途径,对电池的器件进行了优化。通过性能测试,确定了染料M2敏化的太阳能电池的最优化条件：在异丙醇的染浴中加入浓度为5mM的CDCA,液态电解质中含1.0M的TBP。在最优化条件下,染料M2的DSCs的转换效率达到了5.96%(Jsc=13.28 mA cm-2,Voc=649mV,ff=0.69)的光电转换效率。同时,研究了准固态电池的性能与稳定性,其光电转换效率略低于液态电池,但是稳定性大幅提升,经过1000小时的加速老化,效率分别为最佳值的97%,95%,98%和99%。第五章为了进一步拓展敏化剂的光谱吸收范围,有效提高染料分子内电荷转移效率和稳定性,将具有强吸电子性能的苯并噻二唑单元引入到含有亚氨基联芪的染料中,构建D-A-π-A新型敏化剂S1-S4。分别研究了含有苯并噻二唑乙炔(S3和S4)和苯并噻二唑单元(S1和S2)的染料的吸收光谱和光伏性能,发现三键的引入,并没有使吸收光谱发生红移,反而降低了光电转换效率。进一步研究了不同的共轭桥对敏化剂性能的影响,实验结果表明,虽然以苯环为共轭桥的染料(S2和S4)比以噻吩为共轭桥的染料(S1和S3),吸收光谱发生了蓝移,但是LUMO轨道能级提高,有助于电子注入效率增强,从而提高光电转换效率。光伏性能研究显示：基于苯并噻二唑单元和苯环共轭桥染料S2的性能最好,未经优化时,染料S1-S4的光电转换效率分别为5.16%,5.36%,1.39%和2.86%。利用在染浴中加入共吸附剂、调整电解质中TBP的浓度以及优化Ti02电极厚度三种方法,对染料的电池器件进行了优化,最高的光电转换效率达到了6.71%(Jsc=13.69 mA cm-2,Voc=722mV,ff=0.68).同时制作了准固态电解质的电池,光电转换效率达到4.91%(Jsc=10.65 mA cm-2,Voc=673mV,ff=0.68),稳定性得到显著提高,在1000 h光照下,效率仍为最佳值的97%。第六章针对含苯并[c]噻吩单元的敏化染料(X1-X2)的光物理、电化学性能、光电转化效率和稳定性评价等方面开展了系统的研究。研究表明：随着染料X2共轭体系的增大,吸收光谱大大拓宽,但是同时加剧了染料的聚集。通过在染浴中添加鹅去氧胆酸作为共吸附剂,优化Ti02电极的厚度、改变电解质中TBP的浓度等方法,对染料的电池器件进行了优化,染料X1和X2的转换效率达到了4.97%和2.14%,分别提升了27.3%和28.5%。对两个染料的准固态电池性能进行了研究,在长时间加速测试中都表现出良好的稳定性,在1000 h光照下,光伏参数仍为最佳值的95%。第七章研究了两个基于三苯胺和苯并噻二唑的菁染料Ⅰ和Ⅱ的光物理、电化学性能和太阳电池的光伏性能。在AM1.5G标准光源下,两个染料未经CDCA优化的最高入射单色光子-电子转化效率值分别达到了57%和78%,其光电转换效率分别为2.40%和2.97%。这说明三苯胺和苯并噻二唑单元连接键不同对电池的光伏性能有影响,其连接键为三键时具有更好的电荷传输性能。针对菁染料容易发生H-聚集和J-聚集的特点,我们采用了先浸泡共吸附剂CDCA的方法来抑制染料聚集态的产生,达到了较好的效果,光电转换效率分别增加了7.9%和10.4%。更多还原

【Abstract】 Dye sensitized solar cells (DSCs) are one kind of solar cells which can convert light to electricity by means of harvesting the solar irradiation by the sensitizer anchored onto the semiconductor surface. DSCs have attracted considerable attention in scientific and industrial research. DSCs also offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. The photoelectric conversion efficiency and long-term stability of DSCs are two key issues for their practical applications. In this thesis, the performance and stability of aromatic amine-based cells were systematically studied through coadsorption of CDCA, as well as optimizing the inorganic semiconductor electrode and the electrolyte solution. The main contents and results are generalized as follows:In Chapter 1, the basic definition on the structure and principle for dye-sensitized solar cells, and the performance parameters of solar cells are introduced. On this basis, recent progress of high-efficiency sensitizers for dye-sensitized solar cells is reviewed. Then the research strategy of the thesis is presented.In chapter 2, the fabrication processes and measure methods for DSCs were described, with an emphasis on fabricating nano-scale titanium dioxide colloide and the electrode.In chapter 3, the effects of chenodeoxycholic acid (CDCA) in a dye solution as a co-adsorbent on the photovoltaic performance of DSCs based upon two organic dyes containing phenothiazine and triarylamine segments (P1 and P2) were investigated. It was found that the coadsorption of CDCA can hinder the formation of dye aggregates and improve electron injection and thus Jsc. When CDCA concentration is 10 mM, the photoelectric conversion efficiency of dye P1 and P2 reached the maximum,4.80% and 5.31%, respectively, improved by 33% and 25% in comparison with those without CDCA. Electrochemical impedance data indicate that the electron lifetime was improved by coadsorption of CDCA, accounting for the significant improvement of Voc.In chapter 4, the iminostibene and iminodibenzyl moieties were introduced into the organic sensitizer for the first time. The photophysical, electrochemical and photovoltaic properties of the iminostilbene dyes M1-M4 have been studied in detail. With the extension of the conjugated system, the absorption band red shifted and molar extinction coefficient increased. Dye M2 containing iminostibene and vinyl thiophene has the largest conjugated system and the lowest LUMO orbital energy. These characters are greatly favorable for improving the photoelectric conversion efficiency. Compared with the triphenylamine analogues, iminostilbene dyes showed much better photovoltaic performance. It indicated that iminostilbene unit was a kind of excellent electron donor. Further comparison revealed that the sensitizer with iminostibene as electron donor (M2 and M4) showed better performance than the iminodibenzyl derivatives (Ml and M3). In order to solve the problem of dye aggregation, chenodeoxycholic acid was used as a coabsorbent, concentration of 4-tert-butyl pyridine (TBP) in electrolyte was changed and various solvents, such as dichloromethane, ethanol, isopropanol, tert-butyl alcohol, toluene, methanol and tetrahydrofuran were applied into the dye bath. After a series of tests, the optimal conditions based on sensitizer M2 were determined:a isopropyl alcohol dye bath containing 5 mM CDCA, the liquid electrolyte with 1.0M of TBP. In the optimum conditions, the conversion efficiency based on dye M2 reached 5.96%(Jsc=13.28 mA cm-2, Voc=649mV, ff=0.69). Meanwhile, the quasi-solid DSCs performance and stability was studied, and its photoelectric conversion efficiency slightly lower than the liquid DSCs, but the stability increased substantially, the cells based on M1-M4 still retained>96% of its maximum efficiency after 1000 h accelerated tests under full sunlight soaking at 55℃.In chapter 5, in order to expand the absorption spectrum absorption, improve the efficiency of intramolecular charge transfer and the stability of DSCs, benzothiadiazole with strong electron-withdrawing ability was introduced into the iminostilbene dyes, constructing a new type of D-A-π-A sensitizer (S1-S4). The UV spectra and photovoltaic properties of sensitizers involving benzothiadiazole acetylene (S3 and S4) and benzothiadiazole dyes (S1 and S2) were investigated. When the molecular size of dye S3 and S4 increased, their absorption bands did not undergo redshift and the photoelectric conversion efficiency decreased. The effect of different conjugated bridge on the sensitizer’s performance was also investigated. The dye with phenyl (S2 and S4) as bridging unit showed better performance than thiophyl (S1 and S3). Although absorption spectrua were blue-shifted, the LUMO orbital energy level increased. In consequence, the electron injection efficiency, monochromatic photoelectric conversion efficiency and conversion efficiency was improved significantly. The photovoltaic results displayed that dye S2 had the best performance. The photoelectric conversion efficiency of S1-S4 without optimization were 5.16%,5.36%,1.39% and 2.86%, respectively. Great efforts on optimization of the DSCs devices have been made by adding co-adsorbent, changing the concentration of TBP in the electrolyte and optimizing the TiO2 electrode. Dye S2 exhibited impressive efficiencies of 6.71% and 4.91% with liquid electrolyte and solvent-free ionic electrolyte under AM 1.5 G respectively, and showed an excellent stability under light soaking at 55℃for 1000 h.In Chater 6, the photophysical, electrochemical, photovoltaic properties and stability of the benzo[c]thiophene sensitizer were systemically investigated and optimized. The absorption band red-shifted, when a large conjugated spacer was introduced into the sensitizer, meanwhile the aggregation of the dye was also formed. The efficiency was enhanced by using chenodeoxycholic acid (CDCA) as a co-adsorbent, optimizing the electrolyte concentration and electrode thickness to hinder the formation of dye aggregates. The conversion efficiency of dye X1 and X2 reached 4.97%(Jsc=13.44mA cm-2, Voc=592mV,ff=0.63) and 2.14% (Jsc=6.55mA cm-2, Voc=489 mV,ff= 0.67), which have been increased by 27.3% and 28.5%, respectively. The quasi-solid DSCs based on X1 still retained>95% of its maximum efficiency after 1000 h accelerated tests under full sunlight soaking at 55℃In chapter 7, the absorption spectra, electrochemical and photovoltaic properties of two cyanine dyes containing triphenylamine and benzothiadiazole moieties have been extensively investigated. Under irradiation of AM 1.5 G simulated solar light (100 mW cm-2), before optimization the IPCE maxima of the two cyanine dyes reached 57% and 78% and the conversion efficiency were 2.40% and 2.97% respectively. It suggested that the compound in which triphenylamine and benzothiadiazole moieties were connected by triple bond shows better charge transport properties. In order to decrease the H-aggregation and J-aggregation of cyanine dyes, the electrode was immersed in CDCA solution for a little time before sensitized by dyes. The photoelectric conversion efficiency of dyeⅠandⅡreached 2.59% and 3.28%, which have been improved by 7.9% and 10.4%, respectively.更多还原