【作者】 刘一鸣；

【导师】 孙云； Rockett；

【作者基本信息】 南开大学 ， 电子科学与技术， 2012， 博士

【摘要】 铜铟镓硒[Cu（In,Ga）Se₂，简称CIGS]光伏器件的光电转换效率为目前薄膜太阳电池之首，以其优良的器件性能和巨大的商业前景，是目前光伏学术界的研究热点，也是产业界最为关注的新型高效低成本的太阳电池。由于CIGS电池的吸收层是由四种元素构成的复杂化合物，异质结结构又涉及复杂的界面态与隧穿机制，因此CIGS电池的内部器件机理复杂，尚有许多课题有待于进一步研究。器件模拟仿真作为一种有效的理论分析方法，已成为高性能太阳电池研究的重要手段。以往的太阳电池模拟软件在应用于CIGS薄膜太阳电池的仿真研究时，由于存在各自的功能局限，不能很好地满足日益发展的CIGS电池理论研究需要。为了更深入地开展CIGS电池中相关课题的仿真研究，本论文在研究CIGS电池器件物理的基础之上，通过改进一款在国际光伏界流行多年的薄膜太阳电池模拟软件AMPS，从而更有针对性地对CIGS电池特有的一些性质进行仿真研究。改进后的软件程序命名为wxAMPS并已发布，供全球光伏界的研究者免费下载使用。模拟软件的改进工作涉及到众多的理论知识，包括半导体器件物理与数值模拟技术等。而且只有深刻理解了太阳电池载流子输运机理、缺陷导电机理等理论，才能有效地借助器件仿真工具，对CIGS电池的相关机理进行深入地模拟，并正确解释模拟结果背后的原因，从而指导并促进实验研究。因此本论文在前面章节重点阐述了CIGS电池仿真中所涉及的器件物理理论与数值模拟方法。本论文首先在第一章介绍了CIGS电池理论研究的前沿进展，汇总了目前流行的各太阳电池模拟软件，并比较了各软件之间的特点，解释了为何选择在软件AMPS的基础上予以改进与升级。第二章详细讲解了太阳电池通用的器件物理理论。根据半导体物理分析PN结时所用到的准中性区近似，使用解析方法推导了同质结、异质结太阳电池的亮、暗态电流电压特性，并介绍了电池串、并联电阻对器件性能的影响及不同的拟合方法。第三章将解析模型的分析方法，应用于CIGS电池中一些器件特性的探讨，研究了CIGS电池开路电压、品质因子同温度的关系，饱和电流激活能与CIGS禁带宽度的联系，CdS/CIGS异质结界面的费米能级钉扎现象，与缺陷辅助隧穿电流、CIGS吸收层中Ga的背梯度等物理机制对电池性能的影响。因为解析模型需要建立在一定的假设与简化条件基础上，才能获得闭合的解析解，对问题进行分析。而考虑更复杂的器件机制时，这些假设与简化条件不一定满足，此时更精确的器件模拟需要用到数值分析技术。本论文第四章详细研究了使用数值方法进行太阳电池模拟过程中所涉及到的物理模型、仿真思路与具体实现过程。系统阐述了薄膜太阳电池中的缺陷机理与各种缺陷态的数值处理方法，其中包括离散分布、带状分布、高斯分布的受主型或施主型缺陷态，带尾态及中间态，和软件AMPS中尚未考虑的两性缺陷态。研究了异质结太阳电池中更复杂的隧穿机制，如带间隧穿电流、缺陷辅助隧穿电流，并对模拟软件中用到的不同光学模型予以了说明和比较。通过研究薄膜太阳电池模拟的基础理论，与结合CIGS电池仿真的具体需要，软件wxAMPS弥补了原软件AMPS未考虑隧穿电流影响的不足，添加了两种隧穿电流模型，使程序可以更好地分析薄膜太阳电池中的物理机制；并结合牛顿迭代法、Gummel迭代法的优点，改进了模型的求解算法，提高了程序的稳定性与算法的收敛能力。软件还可以模拟材料参数的任意梯度分布对器件性能的影响。第五章通过使用软件wxAMPS，将数值模拟技术应用于CIGS电池的机理研究，并结合前人的实验研究成果，揭示所观察到的宏观实验现象背后的微观物理机制。本章模拟分析了CIGS吸收层的载流子浓度、厚度对电池性能的影响，研究了CIGS电池在低温、弱光下的器件响应，并通过解析模型解释了模拟结果背后的原因。依靠仿真建立的模型发现，对于CIGS电池在低于300K时串联电阻随温度降低而非线性快速增加的现象，是由于CdS/CIGS界面处的势垒影响所致，并由此对学术界在这问题上的争论提出了新的观点和理论解释。本章中还研究出了一种新的仿真方法，可以分析任意Ga梯度对电池性能的影响。结合实测的Ga梯度数据，生成与软件wxAMPS兼容的器件文件，通过比较模拟结果和实验数据，可以有效地对具体Ga含量梯度的效果做出理论分析，并获取更多的器件内部信息。论文最后对博士阶段的主要工作和取得的成果予以了总结，并展望了CIGS薄膜电池器件模拟研究的未来发展方向，及日后模拟软件wxAMPS的进一步研发工作。本论文阐述了当前学术界在CIGS电池理论领域所取得的前沿认识水平，以及本论文的研究工作在其中做出的贡献。更多还原

【Abstract】 As the excellent device performance and the promising manufacture prospect,CuInGaSe₂（CIGS） thin film solar cell is the highest efficiency thin film solar cell,and has become a hot research topic in the Photovoltaic academy field and the most-concerned solar cell by the industry for its high-performance and low cost. Since theabsorber material of CIGS is a complicated compound composed of four elements,and the heterojunction structure is related to the complex interface state and tunnelingmechanism, the inner device principle of CIGS solar cell is difficult to understand,and there are still lots of subjects that need further investigation. Device simulation isa very useful theoretical analysis method, which is one important assistant approachin the high-level solar cell research.For various limitaions, the previous solar cell simulation softwares are notadequate to satify the requirements of the developing CIGS theoretical research. Inorder to better implement the simulation studies on some of the CIGS researchsubjects, this work studies the device physics of CIGS solar cell and updates onepopular simulation code AMPS, and carries out modeling researches on some specifictopics of CIGS solar cell. The improved code is named wxAMPS and has beenpublished for the free download of the international PV community.Lots of theoretical knowledge is involved in the improvements of the simulationsoftware, including semiconductor device physics and numerical modelingtechnology. And only the device mechanisms, such as carriers’ transportationmechanism, defects behaviors, are well understood, the complex mechanisms ofCIGS solar cell can be studied thoroughfully through using simulation toolsefficiently, and the simulation results can be explained correctly. Therefore, thisthesis elucidates the device physics theory and numerical simulation method at firstchapters.In Chapter1, the thesis introduces the frontier progress of CIGS solar celltheoretical research, summarizes a variety of popular modeling software whosefeatures are compared, and explains why AMPS is chosen to be revised and updated. The general solar cell device physics is described in Chapter2. According to thequasi-neutral region assumption which is applied to the PN junction analysis in thesemiconductor physics, the current-voltage characteristic under dark and lightsituations are deduced by the analytical method. The effects and the fitting method ofthe series resistance and shunt resistance are also discussed. In Chapter3, theanalytical approach is applied to study the CIGS solar cell characteristics, analyzesthe dependence of open-circuit voltage to the temperature, of the quality factor to thetemperature, the relationship between the activation energy of saturation current andthe band gap of CIGS material, the Fermi-level pinning phenomena at heterojunctioninterface, and the effects of the trap-assisted tunneling and the Ga back grading to thedevice performance.Assumptions and simplifications are required in the analytical approach toobtain the closed-form solution of the models and fulfill the analysis. But theconditions of these assumptions may not be satisfied in complicated devicemechanisms. Hence, numerical methods are needed for more accurate modeling.Chapter4describes the theory fundamentals of implementing numerical simulationfor the solar cell modeling in detail, and elucidates the defect mechanisms and thenumerical solution for varieties of defect types in thin film solar cell. The tunnelingmodels and optical models used in the solar cell simulation are also explained andcompared.Through studying the basic modeling theory of thin film solar cells andconsidering the specific requirement of CIGS solar cell simulation, wxAMPS makesup for the shortcomings of AMPS which does not consider the tunneling effects, addstwo tunneling models to enhance the code capability to better analyze the physicalmechanism in thin film solar cells. Moreover, wxAMPS improves the solvingalgorithm of the model by combining the Newton iteration method and the Gummeliteration method, and ameliorate the stability and the convergence property of thecode. The wxAMPS softward is also capable of simulating the effects of arbitraygrading of material parameters to the device performance.By using wxAMPS, Chapter5applies the numerical modeling techniche to themechanism studies of CIGS solar cell and compares the experimental resutls, in order to reveal the micro mechanisms behind the macro experimental observations. Thiswork simulates and analyzes the effects of carriers density, thickness of CIGS thinfilm material, studies the device response to the low temperature and low irradiance,and explaines the trend in simulation results by analytical modeling. The simulationresearch found that, it is the effect of CdS/CIGS hetero-interface barrier that causesthe series resistance of CIGS solar cell to increase non-linearly when temperaturedecreases below300K. This thesis proposes a new opinion and theoreticalexplanation for this issue that is still in dabate in the academic field. This chapter alsostudies a new modeling approach that can analyze the effects of arbitray Ga gradingto the cell performance. Based on the measurement Ga gradient data and generating adevice-modeling file that is compatible to wxAMPS, the effects of the experimentalmeasured Ga grading can be analyzed theoretically, and more inner information ofthe device details can be revealed by comparing the experimental data and modelingresults.At last, the main work and the achievements in the Ph.D. project are concluded,and future developments of wxAMPS and the device modeling of CIGS solar cell areforesighted as well. This thesis explicates the latest theoretical understanding on theCIGS solar cell, and the contribution of the work in this dissertation to this field.更多还原