【作者】 陈智；

【导师】 李位；

【作者基本信息】 湖南农业大学 ， 应用化学， 2021， 硕士

【摘要】 随着人口的快速增长以及工业化进程的日益加快,人类社会对能源的需求日益加大。传统化石能源的广泛使用造成了严重环境污染,加之其不可再生且勘测与开采难度越来越高,因此,太阳能逐渐成为科研人员的研究重点。目前以高纯硅、二硒铜铟等半导体为光捕获材料的薄膜太阳能电池已进入商业化阶段,但由于硅造价高昂以及铟等贵金属的限制供应使得他们的进一步应用受到限制。因此,寻找其他替代半导体材料成为当前的工作重心。在此背景下,多元化合物半导体,过渡金属氧化物,以及铅卤钙钛矿等材料由于其优异的光学、电学、化学、物理等性能成为现今的研究热点。为了进一步提高半导体光伏器件的性能,光电转换过程中所涉及的光物理过程相关的研究必不可少。本论文针对Cu₂Zn Sn S₄、Bi VO₄以及MAPb I₃材料中的非辐射电子-空穴复合过程,运用非绝热分子动力学与时域密度泛函理论相结合的方法,系统地研究了点缺陷以及其他外界因素（如压强）对材料光激发动力学的影响。研究结果表明:（1）Cu₂Zn Sn S₄材料中性硫空位的引入会降低电荷重组速率,而+2价硫空位体系由于子隙态的引入会加速电荷复合。（2）Bi VO₄中氧空位的引入,减小了带隙,增强了非绝热耦合矢以及延长了量子退相干过程,加快了电荷的直接复合。（3）加压会减小MAPb I₃材料Pb-I键长,增强Pb-s与I-p轨道之间反键耦合,提高价带顶能量,窄化带隙;同时,压力的增加会导致Pb、I原子波动加快,增大非绝热耦合矢;然而,更快的量子-经典退相过程克服了能隙窄化和非绝热耦合矢增大所带来的不利影响,抑制了电子-空穴的复合。本论文由以下六部分构成。第一章对半导体材料以及太阳能电池相关背景做了简要介绍。第二章介绍了计算模拟中所采用的理论方法及其发展历程。第三章调查了Cu₂Zn Sn S₄材料中硫空位不同电荷态对激发态载流子寿命的影响。第四章揭示了单斜钒酸铋中氧空位对器件光电性能的影响。第五章从原子尺度揭示了压强条件下MAPb I₃带隙与载流子寿命的反相关性。最后,我们对本论文中的所有工作进行总结与展望。更多还原

【Abstract】 The rapid growth of population and industrialization have led to the increasing demand for energy consumption.Large-scale application of traditional fossil energy has caused serious environmental pollution.In addition,fossil energy is non-renewable.Therefore,utilization of solar energy has become the main focus for most researchers.At present,the thin-film solar cells based on Si and In Cu Se₂ have reached the commercialization stage,but high cost limit their extensive applications.Search of other alternative semiconductor materials is center to the present work.Considerable works have been devoted to this topic.Particularly,the quaternary semiconducting compound,transition metal oxide,and lead halide perovskite materials have been under most investigations because of their excellent optical,electrical,chemical,and physical properties.In order to improve the performance of semiconductor photovoltaic devices,it is necessary to study the photophysical processes involved the photoelectric conversion.This paper,focusing on non-radiative electron-hole recombination in Cu₂Zn Sn S₄,Bi VO₄,and MAPb I₃ materials,we studied in detail the influences of point defects and external factor,such as pressure,on the photoexcitation dynamics by combining non-adiabatic molecular dynamics（NA-MD）and time-dependent density functional theory（TD-DFT）.Our research results are summarized below:（1）Introduction of neutral sulfur vacancy in Cu₂Zn Sn S₄ decreases the charge recombination rate,whereas doubly positively charged sulfur vacancy accelerates charge recombination owing to the introduction of the sub-gap state.（2）An oxygen vacancy in Bi VO₄ reduces the band gap,enhances the NA coupling,and extends the quantum decoherence,these factors directly increases nonradiative charge recombination process.（3）Higher pressure in MAPb I₃perovskite reduces the Pb-I bond length,enhances the antibonding coupling between Pb-s and I-p orbitals,which shifts up the orbital energy of valance band maximum（VBM）and decreases the band gap.Meanwhile,higher pressure leads to greater fluctuations of Pb and I atoms,this increases the NA coupling.However,the faster decoherence process overcomes the adverse effects of smaller energy gap and the stronger NA coupling,leading to slower electron-hole recombination.This paper is organized as the following chapters.Chapter 1gave a brief introduction of semiconductor materials and operation mechanism of solar cells.Chapter 2 introduced the theoretical method and computational methodology.In Chapter 3,we elucidated the effect of sulfur vacancies on nonradiative recombination dynamics in Cu₂Zn Sn S₄ solar absorbers.In Chapter 4,the mechanism of oxygen vacancy mediated nonradiative charge recombination in Bi VO₄has been investigated.Chapter 5 rationalized the anti-correction between band gap and excited carrier lifetime under different pressure in MAPb I₃.Finally,we made conclusions and perspective.更多还原