用于光催化裂解水的硫化锌镉固溶体中本征缺陷效应的理论研究

Hydrogen production directly from water splitting by photocatalysts under solar light irradiation is a promising way to solve the world energy crisis. A great deal of research has focused on looking for efficient and stable photocatalysts.This project aims to theoretically investigate the native defect effects in ZnxCd1-xS solid solutions for photocatalystic water splitting. We plan to calculate the formation energy, thermodynamic transition levels of native defects in the ZnxCd1-xS solid solutions by using a special quasi-random structures (SQS) approach combined with the well-tested Heyd, Scuseria and Ernzerhof (HSE) hybrid functionals density functional theory. Band structures, charge distributions, the carrier effective mass, and carrier concentration of the photocatalysts with and without the dominant native defects will be studied in our project. We''ll also investigate the spatial separation of charge carriers promoted by the native defects which can act as electron or hole pools. The ways to separate the electron-hole pairs and to suppress the electron-hole recombination centers will be discussed in the process of photocatalystic water splitting.This project will provide the theoretical support for realization of the large scale applied water splitting photocatalysts.

本项目旨在研究本征缺陷在闪锌矿结构的硫化锌镉（ZnxCd1-xS）固溶体光催化裂解水过程中所起的重要作用。应用特殊准随机结构模型结合混合密度泛函理论计算硫化锌镉固溶体中各种本征缺陷的形成能、转变能级，以确定该类半导体中主要本征缺陷；计算缺陷对硫化锌镉固溶体材料电荷分布的影响，缺陷导致其能带结构的变化，以及缺陷对于载流子有效质量和浓度等输运性能的影响；探讨如何利用缺陷有效分离光催化产生的电子-空穴对，抑制电子和空穴在输运过程中的复合，从缺陷角度探寻有效提高其光催化剂裂解水效率的可行方法。

本项目按照申请书的计划进行了硫化锌镉固溶体本征缺陷的研究，探讨了这些缺陷特性在光催化裂解水过程中所起的作用。利用了特殊准随机结构模型生成32个原子的锌镉互溶闪锌矿硫化锌镉固溶体结构，构造了128个原子超元胞结构的本征缺陷模型。调整了Heyd,Scuseria and Ernzerhof (HSE)混合密度泛函理论中Hartree Fock(HF)交换关联势组分浓度，应用了30%HF组分的混合关联势作为本征缺陷形成能的计算方法。通过不同生长状态下缺陷各种荷电态的形成能与费米面的关系确定了硫化锌镉中主要本征缺陷类型为: 锌间隙、镉间隙、硫空位、镉空位、锌空位。通过电子态密度的计算发现锌间隙和镉间隙可以缩窄禁带宽度而有利于可见光的吸收，而硫空位能增加导带底的电子态密度但不能缩窄禁带宽度。分析了主要本征缺产生的电荷分布，发现硫空位、镉空位和锌空位可以产生的较为明显的电荷分离效应。最后，本项目讨论了缺陷的电荷分离效应对硫化锌镉光催化裂解水过程中电子空穴的输运性能以及生成氢气效率的影响。