中文摘要：

半导体光伏材料的发展在过去60多年中表现出了清晰的多元化趋势.从20世纪50年代的一元Si太阳能电池,到20世纪60年代的GaAs和CdTe电池、70年代的CuInSe2电池、80年代的Cu（In,Ga）Se2、90年代的Cu2ZnSnS4电池,再到最近的Cu2ZnSn（S,Se）4和CH3NH3PbI3电池,组成光伏半导体的元素种类从一元逐渐增多到五元.元素种类的增多使得半导体物性调控的自由度增多,物性更加丰富,因而能满足光伏等器件应用的需要.但是,组分元素种类的增多也导致半导体中晶格点缺陷的种类大幅增加,可能对其光学、电学性质和光伏性能产生显著影响.近20年来,第一性原理计算被广泛应用于半导体中晶格点缺陷的理论预测,相对于间接的实验手段,第一性原理计算具有更加直接的、明确的优势,并且能对各种点缺陷进行快速的研究.对于缺陷种类众多的多元半导体体系,第一性原理计算能预测各种点缺陷的微观构型、浓度和跃迁（离化）能级位置,从而揭示其对光电性质的影响,发现影响器件性能的关键缺陷.因而,相关的计算结果对于实验研究有直接、重要的指导意义.本文将首先介绍半导体点缺陷研究的第一性原理计算模型和计算流程;然后,总结近5年来两类新型光伏半导体材料,类似闪锌矿结构的Cu2ZnSn（S,Se）4半导体和有机-无机杂化的钙钛矿结构CH3NH3PbI3半导体的点缺陷性质;以这两类体系为例,介绍多元半导体缺陷性质的独特特征及其对太阳能电池器件性能的影响.

英文摘要：

In the past 60 years＇ development of photovoltaic semiconductors,the number of component elements has increased steadily,i.e.,from silicon in the 1950 s,to GaAs and CdTe in the 1960 s,to CuInSe2 in the 1970 s,to Cu（In,Ga） Se2 in the1980 s,to Cu2ZnSnS4 in the 1990 s,and to recent Cu2ZnSn（S,Se）4 and CH3NH3PbI3.Whereas the material properties become more flexible as a result of the increased number of elements,and multinary compound semiconductors feature a dramatic increase of possible point defects in the lattice,which can significantly influence the optical and electrical properties and ultimately the photovoltaic performance.It is challenging to characterize the various point defects and defect pairs experimentally.During the last 20 years,first-principles calculations based on density functional theory（DFT）have offered an alternative method of overcoming the difficulties in experimental study,and widely used in predicting the defect properties of semiconductors.Compared with the available experimental methods,the first-principles calculations are fast,direct and exact since all possible defects can be investigated one by one.This advantage is especially crucial in the study of multinary compound semiconductors which have a large number of possible defects.Through calculating the formation energies,concentration and transition（ionization） energy levels of various possible defects,we can study their influences on the device performance and then identify the dominant defects that are critical for the further optimization of the performance.In this paper,we introduce the first-principles calculation model and procedure for studying the point defects in materials.We focus on the hybrid scheme which combines the advantages of both special k-points and Γ-point-only approaches.The shortcomings of the presentcalculation model are discussed,with the possible solutions proposed.And then,we review the recent progress in the study of the point defects in two types of multinary photovoltaic semiconductors,