基于应变与掺杂设计高效光伏材料

发布时间：2017-12-27 10:43

本文关键词：基于应变与掺杂设计高效光伏材料　出处：《苏州科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：高效利用太阳能是解决能源危机和环境问题的最佳途径。通过应变和掺杂调控材料带隙,提高太阳能吸收效率是当前的研究热点。本论文用第一性原理方法,研究应变对SrTcO_3带隙的影响、掺杂对BaTiO_3带隙的影响,探讨它们用作太阳能电池材料的可能性。第一章回顾了一些太阳能电池材料的研究历程;第二章介绍了本文所涉及的理论和计算方法,包括密度泛函理论、局域密度近似(LDA)、广义梯度近似(GGA)和杂化密度泛函(HSE)方法;第三章用GGA+U方法研究了SrTcO_3在双轴应变下的电子结构,讨论了应变对带隙的调控;第四章用杂化密度泛函方法研究了掺杂对BaTiO_3带隙的调控。第五章为总结与展望。在第三章中,用GGA+U方法探索了双轴应变对SrTcO_3带隙的调控及调控机理。结果表明,无论是压缩应变还是拉伸应变,体系的光学带隙都减小。当SrTcO_3生长在四种常用基片SrTiO_3(STO)/La_(0.3)Sr_(0.7)Al_(0.35)Ta_(0.35)O_9(LSAT)/NdGaO_3(NGO)/La Al O3(LAO)上,带隙值变为1.56/1.47/1.43/1.12 eV,符合高效太阳能电池材料带隙范围。由电子结构分析,可得到带隙调控的机理:压缩应变增强时,导带底(源于Tc原子的d3z2-r2态)向费米能级移动,而价带顶(源于dyz态)基本不移动,使带隙降低。在第四章中,用HSE方法计算得到BaTiO_3的带隙为3.3 eV,与实验值(3.4 eV)符合得很好。用该方法研究Co单掺杂、Pd单掺杂以及(Co,Pd)共掺杂对体材料BaTiO_3带隙的影响。发现有4种体系符合高效太阳能电池材料的带隙要求:BaTi_(0.875)Pd_(0.125)O_3、BaTi_(0.875)Co_(0.125)O_(2.875)、BaTi_(0.75)Co_(0.125)Pd_(0.125)O_(2.75)、BaTi_(0.926)Co_(0.037)Pd_(0.037)O_(2.926)带隙分别为1.95 eV、1.85 eV、1.95 eV、1.90 eV。电子结构分析表明,Pd掺杂引入的Pd_4d态提供新的导带底,比原来Ti_3d导带底更靠近费米面,从而降低带隙。对于Co掺杂情形,Co_3d能带稍稍跨过费米面,产生部分空穴,当氧空位存在,氧空位提供的电子填满这些空穴,产生新的能级较高的价带顶,使带隙减小。对于(Co,Pd)共掺杂情形,价带顶升高与导带底降低同时发生,使带隙大大减小。本论文工作可为研制高效太阳能电池材料提供重要的理论依据。
[Abstract]:The efficient use of solar energy is the best way to solve the energy crisis and environmental problems. It is a hot topic to improve the efficiency of solar energy absorption by adjusting the band gap of material by strain and doping. In this paper, the first principles method is used to study the effect of strain on the SrTcO_3 band gap and the influence of doping on the BaTiO_3 band gap, and to explore the possibility of them being used as solar cell materials. The first chapter reviews some of the solar cell materials research progress; the second chapter introduces the theory and method mentioned in this article, including density functional theory, local density approximation (LDA) and generalized gradient approximation (GGA) and hybrid density functional (HSE) method; the third chapter studies the electronic structure of SrTcO_3 under biaxial strain using GGA+U method, discusses the regulation of strain on the band gap; the fourth chapter studies the regulation of BaTiO_3 doping on the band gap by using the hybrid density functional method. The fifth chapter is the summary and prospect. In the third chapter, the GGA+U method is used to explore the regulation and regulation mechanism of SrTcO_3 band gap with biaxial strain. The results show that both the compression strain and the tensile strain decrease the optical band gap of the system. When SrTcO_3 is grown on four commonly used substrates, SrTiO_3 (STO) /La_ (0.3) Sr_ (0.7) Al_ (0.35) Ta_ (0.35) O_9 (LSAT) /NdGaO_3 (NGO), LSAT, the band gap value is changed to zero, which is consistent with the high efficiency solar cell material band gap range. The mechanism of band gap control can be obtained by analyzing the electronic structure. When the compression strain is enhanced, the conduction band bottom (the d3z2-r2 state from Tc atom) moves to Fermi level, while the valence band top (from dyz state) basically does not move and makes the band gap decrease. In the fourth chapter, the band gap of BaTiO_3 is calculated by HSE method. The band gap is 3.3 eV, which is in good agreement with the experimental value (3.4 eV). The effect of Co single doping, Pd single doping and (Co, Pd) Co doping on the BaTiO_3 band gap of the bulk material was investigated by this method. Find that there are 4 kinds of system meet the requirements of band gap high efficiency solar cell materials: BaTi_ (0.875) Pd_ (0.125) O_3, BaTi_ (0.875) Co_ (0.125) O_ (2.875), BaTi_ (0.75) Co_ (0.125) Pd_ (0.125) O_ (2.75), BaTi_ (0.926) Co_ (0.037) Pd_ (0.037) O_ (2.926) band gap were 1.95 eV, 1.85 eV, 1.95 eV, 1.90 eV. The analysis shows that the electronic structure of Pd doped Pd_4d state introduced new conduction band bottom, the bottom of the conduction band more than the original Ti_3d near the Fermi level, thereby reducing the gap. For Co doping, Co_3d band slightly cross fee of rice, which part of hole, when the oxygen vacancy exists, fill the hole oxygen vacancy provides electrons, produce new energy high valence band gap decreases, the. In the case of (Co, Pd) Co doping, the rise of the valence band top and the lower guide band lower at the same time, so that the band gap is greatly reduced. The work of this paper can provide an important theoretical basis for the development of high efficiency solar cell materials.
【学位授予单位】：苏州科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM914.4;O482.3

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