Gettering of impurities in silicon: delivering quantitative understanding to improve photovoltaics

光化学有潜力满足世界所有的能源需求。光电池市场由晶体硅制成的电池主导，占当今产量的80%以上。虽然其他技术正在研究中，但硅的丰度、化学稳定性、密度、带隙和无毒性质意味着它肯定会在至少中期内发挥主导作用。超过一半的体硅太阳能电池是由多晶硅（mc-Si）晶片制成的。虽然多晶硅光电转换器的效率比单晶光电转换器低，但其生产成本低得多，这意味着这些技术目前具有同等的商业可行性。Mc-Si通过铸造生产，通常使用低等级原料，因此填充有扩展缺陷（位错、晶界和沉淀物）和过渡金属杂质点缺陷。光生载流子在这种缺陷处的迁移是导致mc-Si电池效率降低的主要原因。吸杂工艺通常用于重新分布缺陷或将其从材料中去除。然而，这些方法并不完全有效。其中一个主要原因是缺陷之间的相互作用阻止了它们被吸收。该项目旨在进一步了解缺陷相互作用的mc-Si。过渡金属（特别是铁）和扩展缺陷（特别是位错和氧化物沉淀）之间的相互作用的热力学将进行实验研究。还将研究关键扩展缺陷的钝化。所获得的基本知识应允许开发新的或修改的吸杂工艺，其最终目的是促进使用更脏（因此更便宜）的硅光催化剂的原料。

Photovoltaics have the potential to supply all the world's energy needs. The market for photovoltaics is dominated by cells made from crystalline silicon, which account for more than 80% of today's production. Whilst other technologies are being researched, silicon's abundance, chemical stability, density, band gap and non-toxic nature mean that is certain to play a leading role in at least the medium term. More than half of bulk silicon solar cells are fabricated from multicrystalline silicon (mc-Si) wafers. Although mc-Si photovoltaics have lower efficiencies than their single-crystal counterparts, their substantially lower production costs means the technologies have equal commercial viability at present. Mc-Si is produced by casting, often using a low grade feedstock, and is consequently packed with extended defects (dislocations, grain boundaries and precipitates) and transition metal impurity point defects. Recombination of photogenerated charge carriers at such defects is a major reason for the reduced efficiency of mc-Si cells. Gettering processes are routinely used either to redistribute the defects or remove them from the material. However, such processes are not completely effective. One of the major reasons for this is that the interaction between defects prevents them being gettered. This project aims to further the fundamental understanding of defect interactions in mc-Si. The thermodynamics of interactions between transition metals (particularly iron) and extended defects (particularly dislocations and oxide precipitates) will be studied experimentally. Passivation of key extended defects will also be investigated. The fundamental knowledge obtained should allow the development of new or modified gettering processes with the ultimate aim of facilitating the use of dirtier (hence cheaper) feedstocks for silicon photovoltaics.