论文标题
硅晶界中的氧隔离的初始研究：应变和空缺的作用
Ab initio study of oxygen segregation in silicon grain boundaries: the role of strain and vacancies
论文作者
论文摘要
多晶硅被广泛用于生产低成本和高效率太阳能电池。在晶体生长和装置制造过程中，硅太阳能电池包含晶界（GB），这是原子杂质（例如氧原子）的优先分离位点。 GB可以诱导载体重组可显着降低载体寿命，因此对SI设备的性能有害。我们研究了σ3{111} Si GB的结构，能量和电子特性之间的相关性，在空缺，应变和多个O分离的情况下。在应变和空缺的情况下，对GBS的结构和能量特性的研究提供了对控制氧原子隔离的复杂机制的准确描述。我们分析了拉伸和压缩应变，并获得了O杂质周围的局部拉伸应变对于分离非常有效。我们还研究了在SI空缺存在下的多种O杂质的作用，发现隔离是恢复四面体共价键的那些结构的最爱。空缺的存在吸引了原子杂质以恢复电子稳定性：间隙杂质变成替代性。该分析是将σ3{111} si GB中电子性质变化与在存在应变和空位存在下的o杂质的变化相关的起点。对于每个结构，我们分析了状态的密度及其对原子和状态的投影，带隙，隔离能及其相关性，以表征新能量水平的性质。实际上，了解定义的电子状态的起源将允许优化材料，以减少非辐射电子孔重组，以避免电荷和能量损失，从而提高太阳能电池效率。
Multi-crystalline silicon is widely used for producing low-cost and high-efficiency solar cells. During crystal growth and device fabrication, silicon solar cells contain grain boundaries (GBs) which are preferential segregation sites for atomic impurities such as oxygen atoms. GBs can induce charge carriers recombination significantly reducing carrier lifetimes and therefore they can be detrimental for Si device performance. We studied the correlation between structural, energetic and electronic properties of Σ3{111} Si GB in the presence of vacancies, strain and multiple O segregation. The study of the structural and energetic properties of GBs in the presence of strain and vacancies gives an accurate description of the complex mechanisms that control the segregation of oxygen atoms. We analysed tensile and compressive strain and we obtained that local tensile strain around O impurities is very effective for segregation. We also studied the role of multiple O impurities in the presence of Si vacancies finding that the segregation is favorite for those structures which have restored tetrahedral covalent bonds. The presence of vacancies attract atomic impurities in order to restore the electronic stability: the interstitial impurity becomes substitutional. This analysis was the starting point to correlate the change of the electronic properties in Σ3{111}Si GBs with O impurities in the presence of strain and vacancies. For each structure we analysed the density of states and its projection on atoms and states, the band gaps, the segregation energy and their correlation in order to characterise the nature of new energy levels. Actually, knowing the origin of defined electronic states would allow the optimization of materials in order to reduce non-radiative electron-hole recombination avoiding charge and energy losses and therefore improving solar cell efficiency.
