染料敏化太阳能电池的器件物理与性能研究

发布时间：2018-09-12 07:58

【摘要】：当前地球人口数量在逐年攀升，化石能源将无法满足人类日益增长的能源需求。寻找并利用可再生能源是全球所关注和研究的热点。在所有的可再生能源中，太阳能是未来最有可能的能源供给方式，，其最主要的利用途径是太阳能发电。近年来，染料敏化太阳能电池（Dye-sensitized solar cells, DSC）因其较低的生产成本与较高的光电转换效率引起了人们的广泛关注，并被认为是最有潜力的第三代太阳能电池。当前，DSC的性能还无法与传统晶体硅太阳能电池相比拟，因此挖掘其性能上的潜力是一项重要而有意义的工作。当今，大量研究者对DSC性能的研究多立足于材料、器件结构等，很少涉及DSC的内部物理机制。探寻DSC器件的物理机制对提升DSC性能有着重要的促进作用。本文从DSC器件物理研究出发，提出了精确、有效的DSC物理机制分析方法与内部物理参数测试方法，并以此为基础探寻提高器件性能的有效途径。首先，基于DSC的等效电路模型，研究了影响DSC光电转换效率的关键因素。利用单结等效电路模型，首次采用遗传算法（Genetic Algorithm, GA）、粒子群算法（Particle Swarm Optimization, PSO）和差分算法（Differential Evolution, DE）分别对DSC的等效电路参数进行了分析和提取。研究发现， PSO算法具有较高的参数精度、抗噪能力和计算效率，是一种准确、高效的DSC参数提取方法。该方法有效解决了DSC器件参数精确提取的技术难题。通过对电路参数的精确提取，发现DSC的内部串联电阻Rs是影响器件性能的重要参数之一。因此，要实现DSC更高的光电转换效率，必须研究降低器件Rs值的有效方法，这为DSC的研究工作指明了方向。其次，研究了通过抑制复合反应提高DSC性能的器件物理机制。复合反应速率与DSC的能量转换效率密切相关，通过抑制复合反应能有效提升光阳极中的有效电子浓度，提高扩散电流密度，增强光阳极中的电子输运能力，亦即降低电池中的Rs。为定量研究复合反应与光阳极中有效电子浓度的对应关系，需对光阳极中自由电子寿命进行准确测量和分析。作为表征复合反应最重要的参数，通常的测量方法和数据处理都比较复杂。本文结合瞬态光电测试方法和Savitzky-Golay滤波技术，提出采用可变级微分平滑方法分析计算DSC中的电子寿命。该研究首次实现了对DSC电子寿命的精确、高速测量，为定量表征DSC的内部复合机制提供了一种可靠的方法。再次，提出了基于稀土元素掺杂的新型氧化物半导体DSC光阳极材料，并对材料的电学、光学性能进行了数值模拟。通过第一性原理计算，发现经稀土元素La掺杂的ZnO材料自由电子密度增加，呈现金属化特性，有效增强了光阳极的电子输运和收集能力，降低了光阳极电阻。同时，La掺杂后ZnO带隙变宽，吸收边蓝移，拓宽了光阳极的透射波段，减少了入射光损失，材料的光吸收率、光反射率也有所降低。这些都有利于提升光吸收层中的入射光子数量，从而实现器件更高的输出电流和能量转换效率。该研究不但揭示了一条提高DSC光电转换效率的有效途径，还揭示了ZnO作为DSC光阳极材料具有很大的应用潜力。最后，提出了利用光学运筹的方法，通过调控光阳极界面来提高DSC的性能。采用光化学催化法在TiO2光阳极镀上薄层银纳米颗粒，通过控制光催化镀银时间以调节纳米颗粒的覆盖量。银纳米颗粒的散射增大光在光阳极中的有效传输距离，提升了太阳光利用率，提高了器件的短路电流密度。降低TiO2纳米颗粒的表面态密度，将减缓光生电子与电解液中氧化物的复合反应，改善光生电子在介孔TiO2薄膜内的传输，从而降低内部串联电阻Rs。研究结果表明，利用该方法，DSC的光电转换效率由5.97％提升至6.86％。该研究所提出的DSC光阳极界面调控技术，能有效提高器件的光电转换效率，并对DSC设计工作有重要的指导意义。
[Abstract]:As the population of the earth is increasing year by year, fossil energy will not be able to meet the increasing energy demand of mankind. Searching and utilizing renewable energy is the focus of global concern and research. In recent years, dye-sensitized solar cells (DSCs) have attracted much attention due to their low production costs and high photoelectric conversion efficiency, and are considered as the most promising third generation solar cells. The potential of DSC performance is an important and meaningful work. Nowadays, a large number of researchers focus on the material, device structure and so on, seldom on the internal physical mechanism of DSC. Effective DSC physical mechanism analysis method and internal physical parameter measurement method are used to explore effective ways to improve device performance.
Firstly, based on the equivalent circuit model of DSC, the key factors affecting the photoelectric conversion efficiency of DSC are studied. Using the single-junction equivalent circuit model, genetic algorithm (GA), particle swarm optimization (PSO) and differential evolution (DE) are used for the first time to improve the equivalent circuit parameters of DSC respectively. It is found that PSO algorithm is an accurate and efficient method for extracting DSC parameters with high precision, anti-noise ability and computational efficiency. This method effectively solves the technical problem of precise parameter extraction of DSC devices. Therefore, in order to achieve higher photoelectric conversion efficiency of DSC, it is necessary to study effective methods to reduce the Rs value of the device, which points out the direction of DSC research.
Secondly, the mechanism of improving DSC performance by restraining recombination reaction is studied. The recombination reaction rate is closely related to the energy conversion efficiency of DSC. By restraining recombination reaction, the effective electron concentration in the photoanode can be effectively increased, the diffusion current density can be increased, and the electron transport capacity in the photoanode can be enhanced, that is, the Rs in the battery can be reduced. In order to quantitatively study the relationship between the composite reaction and the effective electron concentration in the photocathode, it is necessary to measure and analyze the free electron lifetime of the photocathode accurately. As the most important parameter to characterize the composite reaction, the usual measurement methods and data processing are very complicated. A variable-order differential smoothing method is proposed to analyze and calculate the electron lifetime in DSC. This study is the first time to achieve accurate and high-speed measurement of the electron lifetime of DSC, and provides a reliable method for quantitatively characterizing the internal recombination mechanism of DSC.
Thirdly, a new type of oxide semiconductor DSC photoanode material based on rare earth element doping is proposed, and the electrical and optical properties of the material are simulated numerically. At the same time, the band gap of ZnO doped with La becomes wider, the absorption edge blue shifts, the transmission band of the anode is widened, the loss of incident light is reduced, the optical absorptivity and the optical reflectivity of the material are also reduced. This study not only reveals an effective way to improve the photoelectric conversion efficiency of DSC, but also reveals the potential application of ZnO as a DSC anode material.
Finally, a method of optical operation research is proposed to improve the performance of DSC by adjusting the interface between the photocathode and the anode. A thin layer of silver nanoparticles is deposited on the titanium dioxide photocathode by photochemical catalysis, and the coverage of the nanoparticles is adjusted by controlling the time of photocatalytic silver plating. The utilization ratio of sunlight is increased, the short circuit current density of the device is increased, the surface state density of the nanoparticles is decreased, the composite reaction between photogenerated electrons and oxides in the electrolyte is slowed down, the transmission of photogenerated electrons in the mesoporous TiO2 film is improved, and the internal series resistance Rs is reduced. The conversion efficiency is improved from 5.97% to 6.86%. The proposed DSC photoanode interface control technology can effectively improve the photoelectric conversion efficiency of the device, and has important guiding significance for DSC design.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM914.4

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