【作者】 袁吉仁；

【导师】 沈鸿烈；

【作者基本信息】 南京航空航天大学 ， 凝聚态物理， 2011， 博士

【摘要】 全球性的能源危机和环境恶化正威胁着人类的长期稳定发展，能源与环境问题成了21世纪人类面临的两大主要问题。太阳能光伏发电是解决能源与环境问题，实现人类社会可持续发展的有效途径。然而，和传统发电方式相比，太阳电池光伏发电的成本仍然非常高，这就限制了太阳能光伏发电的大规模应用。因此，寻找太阳电池新材料、开发太阳电池新技术以进一步提高转换效率、降低生产成本是摆在面前的迫切任务。本文正是在上述背景下，结合本课题组承担的国家“863”计划等项目开展了一系列研究工作。本文主要通过数值模拟和理论分析，深入地研究了β-FeSi₂太阳电池和μc-3C-SiC发射极HIT太阳电池以及杂质光伏新概念太阳电池的输运性能，预先为实验制备相关高效太阳电池提供了理论基础和技术支持。主要研究内容和研究结果包括以下几个方面：（1）构建了β-FeSi₂太阳电池的数值模型，并对β-FeSi₂薄膜同质结太阳电池进行了数值研究。得到β-FeSi₂薄膜同质结太阳电池的最优结构参数为：发射区厚度20nm，浓度2×1018cm^-3；基区厚度500nm，浓度1×1016cm^-3。参数优化后的电池性能为：η=16.32%，Jsc=45.88mA/cm²，FF=78.8%，Voc=0.451V。通过计算得到该薄膜电池的理论极限转换效率可以达到21.11%。（2）研究了发射区参数、光入射面、界面态和各种复合机制等因素对β-FeSi₂/c-Si异质结太阳电池性能的影响。结果表明：采用p型β-FeSi₂与n型c-Si配置的异质结电池性能更佳，且太阳光从β-FeSi₂面入射要好于从Si面入射。高的界面态密度会导致很多光生载流子的复合以及产生大的反向饱和电流。由于β-FeSi₂的光吸收系数非常大，使得β-FeSi₂太阳电池性能对表面复合速度非常敏感，因而钝化β-FeSi₂表面是制备高效β-FeSi₂太阳电池的关键。同时，俄歇复合和辐射复合对器件性能影响较小，而当体SRH复合寿命大于1μs时则SRH复合对电池转换效率影响很小。β-FeSi₂/c-Si异质结太阳电池的发射区优化参数为：p型发射区β-FeSi₂薄膜厚度350nm，掺杂浓度为2×10¹⁷cm^-3，转换效率可以达到19.49%。β-FeSi₂/c-Si异质结太阳电池的理论极限效率可以达到28.12%。（3）提出把β-FeSi₂电池用作叠层电池的底电池，使太阳光谱利用范围扩宽到近红外区1400nm以上，并从理论上详细探讨了各种因素对a-Si/μc-Si/β-FeSi₂叠层薄膜电池性能的影响。结果表明：a-Si/μc-Si/β-FeSi₂叠层电池的子电池光吸收层的最优厚度分别为260nm/900nm/40nm，此时各子电池的电流比较匹配，电池转换效率可以达到19.80%。μc-Si子电池的优化带隙为1.30eV，可使a-Si/μc-Si/β-FeSi₂叠层薄膜电池的转换效率最高。对于a-Si/μc-Si/β-FeSi₂叠层电池，AM0光谱辐照时转换效率最高，其次是AM1.0，最小的是AM1.5G。该叠层薄膜电池的转换效率温度系数为-0.308%/K，比μc-Si单结电池要小，仅大于a-Si单结电池，因此具有很好的温度系数，适合于热带地区的使用。当改善a-Si和μc-Si材料的品质后，a-Si/μc-Si/β-FeSi₂叠层薄膜电池的短路电流密度可以达到16mA/cm2左右，且电池转换效率可能达到24.50%。（4）提出用μc-3C-SiC材料取代a-Si作为HIT电池的发射极。结果表明：用μc-3C-SiC材料作HIT太阳电池的发射极，可以有效地减少短波区光吸收损失，改善蓝光光谱响应，使得电池的短路电流密度增大，进而提高电池的转换效率。（5）针对杂质光伏新概念太阳电池，研究了分别掺入单能级IPV杂质Te和In对晶体硅电池性能的影响。结果表明：掺入单能级IPV杂质Te，电池的短路电流密度可以增加5.38mA/cm²，电池转换效率净增量为2.79%。IPV效应使电池的近红外光谱响应产生了延展，且当电池内部陷光越好时，近红外光谱响应延展越宽。对于靠近价（导）带边的受（施）主型IPV杂质，电子（空穴）热俘获截面大小对提高IPV电池转换效率有关键作用，可以根据IPV杂质的热俘获截面来判断它们用于IPV电池对提高电池转换效率的潜能。（6）研究了IPV杂质能级位置和双能级IPV杂质Mg对晶体硅电池性能的影响，以及同时掺入In和Tl两种不同IPV杂质时对电池性能的影响。结果表明：对于施主型IPV杂质，当杂质能级位于导带下0.20⁰.25eV区间时，所掺入的杂质将使IPV电池的转换效率净增量最大化。当有两个能级起作用时，能级位置不是较优的能级将分流部分入射的子带光子，使得电池转换效率低于单能级在较优位置起作用时的转换效率。对于掺两种不同的IPV杂质，可以改变其中一种杂质的浓度使电池效率提高。更多还原

【Abstract】 The long-term stable development of humans is under threat due to the global energy crisis andenvironmental degradation. Energy and environment are two major issues in the world during the21stcentury. Solar photovoltaic technology is an effective way of resolving the energy exhaustion andenvironmental pollution and realizing the sustainable development of human society. However,compared to the traditional power generation, the cost of solar photovoltaic technology is still veryhigh, which limits the large-scale application of solar photovoltaic technology. Therefore, it is anurgent task to search for new materials and to develop new technologies for further improving cellefficiency and reducing cell cost.This work has been carried out under the above-mentioned background and by the support of thenational “863” project. The transport properties of β-FeSi₂solar cells and impurity photovoltaic （IPV）solar cells have been investigated by numerical simulation and theory analysis. These research resultscan provide a theory guide for preparing the relating high-efficiency solar cells. Main contents andresults of this study are as follows.（1）The numerical model of β-FeSi₂solar cell has been constructed and β-FeSi₂homojunctionsolar cell has been simulated. The optimal structure parameters of β-FeSi₂homojunction solar cell areas following: emitter thickness20nm, emitter concentration2×1018cm^-3, base thickness500nm, baseconcentration1×1016cm^-3. The corresponding cell performance is η=16.32%, Jsc=45.88mA/cm2,FF=78.8%, and Voc=0.451V. The maximum theoretical efficiency of the cell can reach21.11%.（2）The influences of emitter parameters, light incidence surface, interface states andrecombination mechanism on the β-FeSi₂/c-Si heterojunction solar cell performance have beenstudied. The results show that p-β-FeSi₂/n-c-Si is a good structure configuration and the lightincidence from β-FeSi₂surface is better than that from Si surface. Interface states should beminimized since large interface states can cause more recombination of photocarriers and largereverse saturation current. The very large light absorption coefficient of β-FeSi₂results in the fact thatβ-FeSi₂solar cell performance is very sensitive to surface recombination velocity. Moreover, theAuger recombination and radiative recombination have less impact on device performance. When theSRH recombination lifetime is greater than1μs, the SRH recombination has little effect on cellefficiency. The optimal thickness and concentration for the emitter of p-β-FeSi₂/n-c-Si are350nm and2×10¹⁷cm^-3, respectively. The conversion efficiency of the optimized cell can achieve19.49%. The theoretical limit of efficiency for β-FeSi₂/c-Si heterojunction solar cells can attain28.12%.（3）β-FeSi₂has been applied to the bottom absorber of the tandem solar cell for widening thespectrum response above1400nm. The effects of sub-cell parameters, μc-Si bandgap, spectralirradiance and operating temperature on the a-Si/μc-Si/β-FeSi₂triple-junction solar cell performancehave been investigated. The optimal absorber thickness of sub-cell for a-Si/μc-Si/β-FeSi₂is260,900and40nm, respectively. The efficiency of the optimized cell can achieve19.80%. The optimalbandgap of μc-Si cell is1.30eV. For a-Si/μc-Si/β-FeSi₂tandem cell, when spectral irradiance is AM0,the conversion efficiency is highest, then AM1.0, and the smallest one AM1.5G. Moreover, thetemperature coefficient of conversion efficiency for the tandem cell is-0.308%/K. This value is lowerthan that of μc-Si single-junction cell, and it is only higher than that of a-Si single-junction cell. Whenmaterial quality of a-Si and μc-Si is improved, the short-circuit current density of a-Si/μc-Si/β-FeSi₂can reach around16mA/cm2, and the conversion efficiency may achieve24.50%.（4）μc-3C-SiC material has been proposed as the emitter of the HIT solar cell. The resultindicates that the cell efficiency is improved by using a μc-3C-SiC emitter. The origin of theimprovement is the lower absorption loss of μc-3C-SiC emitter in short-wavelength region.（5）The influences of the Te and In IPV impurities on the crystalline silicon （c-Si） cellperformance have been studied. The short-circuit current density can be increased by5.38mA/cm2and the efficiency can be increased by2.79%due to the incorporation of IPV impurity Te. In addition,IPV effect can extend near-infrared spectral response, and a good light trapping can result in the widerextension of the near-infrared spectral response. Furthermore, the thermal capture cross-section ofelectron （hole） is crucial to the device performance and that of hole （electron） has few influences onthe cell property for acceptor-type （donor-type） impurity level near the valence （conduction） bandedge. These results may help to evaluate the potential of the IPV effect for improving cell efficiencyaccording to the thermal capture cross-sections of the impurity in host semiconductor.（6）The effects of the energy level, and Mg, In, Tl impurity on the IPV c-Si cell performancehave been studied. The optimal energy level for donor-type IPV impurity is at0.20-0.25eV below theconduction band edge. When two levels work, the energy level, which is not at optimal location,would divert some incident sub-band photons, making efficiency less than those with an optimalsingle-level. When two different IPV impurities are introduced into cells, the concentration of oneimpurity can be changed for increasing cell efficiency.更多还原