The structural stability and defect-tolerance of ionic spinel semiconductors for high-efficiency solar cells
The structural stability and defect-tolerance of ionic spinel semiconductors for high-efficiency solar cells
复制标题
DOI：
10.1039/d1ta02409d
复制
发表时间：
2021-06
影响因子：
--
通讯作者：
Hanzhen Liang;Huiwen Xiang;Rui Zhu;Chengyan Liu;Yu Jia
中科院分区：
文献类型：
--
作者：
Hanzhen Liang;Huiwen Xiang;Rui Zhu;Chengyan Liu;Yu Jia
缺陷容限与结构稳定性之间的不相容是阻碍高效太阳能电池广泛应用的严重问题。通常，具有Si/CdTe晶体原型的共价/极性半导体由于其紧凑的四面体结构而表现出很大的结构稳定性，但由于其组成元素的相似电负性，它们呈现出极差的缺陷容限。相比之下，离子半导体，如钙钛矿系列，总是表现出有利的电子性质的本征缺陷所造成的阴离子和阳离子之间的电负性的巨大差距，但结构不稳定，因为稀疏组成的八面体构建块由大阳离子支持。结合共价半导体的稳定骨架和离子化合物的良性缺陷，我们发现HgX_2S_4（X = In，Sc，Y）尖晶石半导体兼具这两种优点。紧密结合的四面体和八面体结构单元确保了结构稳定性和具有离子特征的带边，主要由用于导带最小值（CBM）的Hg-6s/X-ns（d）和用于价带最大值（VBM）的S-3 p轨道控制，使得HgX 2S 4具有缺陷耐受性。具有大的主量子数（n）的空间扩展的Hg-6s/X-ns（d）轨道引起的CBM的显著向下弯曲不仅诱导了合适的光学带隙（其通常在离子化合物中过大），而且促进了n型载流子的形成和输运。研究表明，Hg基硫族化合物尖晶石是一种很有前途的高效太阳能电池材料，同时提出在尖晶石晶体骨架下引入具有离域轨道的阳离子是合成稳定、耐缺陷光伏材料的另一种途径。
Incompatibility between defect-tolerance and structural stability is a severe issue hindering the wide application of high-efficiency solar cells. Usually, covalent/polar semiconductors with a prototype of Si/CdTe crystals exhibit great structural stability due to their compact tetrahedral structure, yet they present extremely poor defect-tolerance arising from the similar electronegativity of their component elements. In contrast, ionic semiconductors, such as perovskite series, always exhibit favorable electronic properties of intrinsic defects caused by the great disparity of electronegativity between anions and cations, but are structurally unstable because of the sparsely composed octahedral building blocks supported by large cations. Combining the stable framework of covalent semiconductors and benign defects of ionic compounds, we find that HgX2S4 (X = In, Sc and Y) spinel semiconductors possess both the merits. The tightly combined tetrahedral and octahedral building blocks ensure the structural stability and the band edge with an ionic characteristic, mainly dominated by Hg-6s/X-ns(d) for the conduction band minimum (CBM) and S-3p orbitals for the valence band maximum (VBM), make HgX2S4 defect-tolerant. The prominent downward bending of the CBM caused by spatially spreading Hg-6s/X-ns(d) orbitals with a large principal quantum number (n) not only induces a suitable optical band gap which is often too large in ionic compounds, but also promotes the formation and transport of n-type carriers. This study shows that Hg-based chalcogenide spinels are promising candidates for high-efficiency solar cells, and suggests that adopting cations with delocalized orbitals under the framework of spinel crystal is an alternative approach for synthesizing stable and defect-tolerant photovoltaic materials.