【作者】 吴强；

【导师】 侯娟；

【作者基本信息】 石河子大学 ， 化学工程（专业学位）， 2018， 硕士

【摘要】 由于化石燃料的紧缺和环境污染的增加,全球科学家们不断寻找可替代性能源。在自然界中存在许多可再生能源,如:风能,氢能,太阳能等。其中太阳能电池是将太阳能转换为电能直接最有效的利用方式。作为第三代太阳能电池,量子点敏化太阳电池（QDSCs）由于具有较高的理论转换效率,工艺简单和低生产成本,引起了科学界的广泛关注。然而,迄今为止,QDSCs的光电转换效率仍然远低于传统的太阳能电池。本论文从QDSCs的基本结构和工作机理为基础,考虑到量子点敏化的光阳极制备方法和级联结构,无机量子点与金属氧化物半导体薄膜以及量子点之间的异质结界面对太阳能电池光电性能的影响。设计了基于CdS/CdSe量子点共敏化体系,通过系统研究QDSCs的不同异质结界面问题以提高光俘获效率,减小界面电荷复合和加快电子传输性能,从而改善QDSCs的光电转换效率（PCE）。主要研究内容可分为以下三个方面:（1）采用溶剂热法制备亚微米级的ZnO球聚体作为光阳极薄膜,通过简单的浸渍法将ZnO球聚体光阳极薄膜浸渍在前驱体溶液Na₂S溶液中,致使ZnO表面Zn²⁺与前驱体溶液中的S^2-反应形成ZnS钝化层包覆在ZnO表面所形成核壳结构应用在CdS/CdSe量子点共敏化太阳能电池。结果表明:ZnO球聚体约为250μm且大小均一,其颗粒之间有较小的间隙导致具有较高的比表面积和较高的光散射效果。此外,ZnS层修饰的ZnO球聚体多孔结构薄膜不但可以提高光俘获能力,而且可以有效地延缓界面电荷复合反应（40.49-138.7Ω）,延长电子寿命（78.96-187.45 ms）。最终,CdS/CdSe敏化的内层ZnS修饰的ZnO球聚体光阳极的PCE达到2.8%,比未修饰电池的PCE（1.89%）提高了48%。（2）利用化学还原法制备还原氧化石墨烯（RGO）应用于QDSCs。基于此,我们系统的研究了RGO的沉积顺序和沉积时间对量子点敏化太阳能电池光学和电化学性能的影响。结果表明:通过水热还原法得到还原程度较为优良的RGO片层,并证明较好地负载在敏化光阳极薄膜表面。同时,通过调控浸渍时间以控制RGO的沉积量,研究基于TiO₂/CdS/CdSe不同时间修饰对光学和光伏性能的影响。由于RGO的光散射效应,可以增强电池光俘获效率,从而提高短路电流密度（13.7-15.8mA/cm²）。在量子点和RGO之间嵌入ZnS钝化层可以延缓界面电荷复合,然而结果表明RGO也可以加快了界面电荷复合导致开路电压（602-572 mV）微弱的降低。最终,通过优化获得最优电极结构为TiO₂/CdS/CdSe/ZnS/RGO,其PCE达到5.28%。（3）ZnS作为无机钝化层应用在QDSCs已被广泛证明可以有效地减小界面电荷复合以改善电池的PCE。基于此,通过简单的连续离子层交互吸附与反应法（SILAR）和化学浴沉积法（CBD）制备多层ZnS钝化层修饰CdS/CdSe共敏化TiO₂光阳极太阳能电池,并且深入系统地研究了多层ZnS层在不同界面位置和沉积层数对光学和电化学性能的影响。结果表明:多层ZnS层修饰的CdS/CdSe量子点共敏化体系构成的级联结构不但可以增强光俘获效率;而且可以有效地抑制不同界面电荷复合（96.6-184.1Ω）,延长电子寿命（135.2-276.2 ms）。同时,在CdS和CdSe界面嵌入的ZnS可以通过在化学浴沉积（CBD）形成CdSe量子点的过程中进行离子交换形成ZnCdS层有利于提高量子产率。最终,在CdS/CdSe共敏化体系中采用三层ZnS层组合修饰,且三层ZnS层沉积层数为2层时,其PCE可达到6.05%,高于传统单一ZnS层修饰的太阳能电池（TiO₂/CdS/CdSe/ZnS,4.80%）。更多还原

【Abstract】 Scientists are looking for alternative energy sources all over the world due to fossil energy shortage and environmental pollution.There are many renewable energy in nature,such as wind energy,hydrogen energy,solar energy and so on.Among them,solar cell,solar energy convented into electrical energy,is the most direct and effective way.Quantum dot sensitized solar cells（QDSCs）,as the third generation of solar cells,have received widespread attention due to its high power conversion efficiency（PCE）,easy synthesis and low cost.However,the PCE of QDSCs is still far lower than that of traditional solar cells.Based on the structure and working mechanism of QDSCs,this work investigated the preparation method of quantum dot sensitized photoanode and cascaded structure,and the effect of heterojunction interfaces within the inorganic quantum dots and the metal oxide film on the performance of QDSCs.The CdS/CdSe quantum dot co-sensitization system was designed to improve the light trapping efficiency,reduce the interfacial charge recombination and accelerate the electron transport efficiency resulted in a high PCE.The main contents has three parts the followed:（1）The ZnO aggregates as photoanode film were prepared by solvothermal method.And then,ZnO film was immersed in the Na₂S solution resulted in reacting the Zn²⁺on the surface of ZnO with S^2-to form the ZnS passivation layer.The passivation layer was coated on the ZnO surface to form the core-shell structure,which was applied in CdS/CdSe QDSCs.As a result,the ZnO aggregates were average size of about 250μm,which had higher light scattering effect and higher specific surface area because of the small gap within the particles.In addition,ZnS modified ZnO aggregates photoanode film can not only improve the light trapping efficiency,but also effectively attenuate interfacial charge recombination（40.49-138.7Ω）and prolong electron lifetime（78.96-187.45 ms）.Finally,the PCE of CdS/CdSe quantum dots sensitized inner-ZnS-modified ZnO photoanode reached 2.8%,which was 48%higher efficiency compared to 1.89%for solar cells without modification.（2）Reduced graphene oxide（RGO）was prepared by chemical reduction method,which was applied in QDSCs.Then,the characterization and comparison of optical and electrochemical properties as well as the performance of the resultant quantum dot-sensitized solar cells（QDSCs）with different immersion time and deposition sequences of RGO have been investigated systematically.As a result,RGO sheet is obtained with better reduction degree and loaded on the surface of sensitized photoanode film.At the same time,the effect of RGO on the optical and photovoltaic properties was studied by adjusting the immersion time to regulate the deposition amount of RGO based on the TiO₂/CdS/CdSe sensitized photoanode.Due to the light scattering effect of RGO,the introduction of RGO demonstrated to enhance the light harvesting and consequently increase the short-circuit current density（13.7-15.8 mA/cm²）.When ZnS inserting between QDs and RGO can effectively block the charge recombination at the interface,however,RGO still may accelerate the interface charge recombination in QDSCs and lead to a slight decrease of the open circuit voltage（602-572 mV）.Finally,the better structure of the device was TiO₂/CdS/CdSe/ZnS/RGO,and then it reached 5.28%of PCE.（3）ZnS as an inorganic passivation layer in QDSCs has been proven to effectively suppress charge recombination resulted in improving the PCE.In the present study,a multi-layer ZnS passivation layer modified CdS/CdSe co-sensitized TiO₂ photoanode solar cell was prepared by successive ionic layer absorption and reaction（SILAR）and chemical bath deposition（CBD）.The complementary effects of multi-ZnS layers on the optical and electrochemical performance of the QDSCs at different interface sites and deposited layers were systematically investigated.This cascade structure is demonstrated to improve the light trapping efficiency,decrease charge recombination（96.6-184.1Ω）and prolong the electron lifetime（135.2-276.2 ms）.Meanwhile,based on ion-exchange by the CBD process,an intermediate ZnCdS layer is formed at the interface between CdS and CdSe,which can enhance the quantum yield.Finally,when the deposited number of ZnS layer at three sites in the CdS/CdSe co-sensitized TiO₂ photoanode was2 layers,the PCE was 6.05%,which was higher than that of the conventional cell（TiO₂/CdS/CdSe/ZnS,4.80%）.更多还原