关键词: Cl掺杂CdTe/
Cl处理CdTe/
高分辨透射电子显微镜/
导电原子力显微镜
English Abstract
The twins structure and electric properties of Cl doped CdTe film by magnetron sputtering
Zhu Zi-Yao1,3,Liu Xiang-Xin3,4,
Jiang Fu-Guo2,
Zhang Yue1
1.School of Materials Science and Engineering, Beihang University, Beijing 100191, China;
2.National Institute of Clean and Low-Carbon Energy, Beijing 102211, China;
3.The Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China;
4.University of Chinese Academy of Sciences, Beijing 100049, China
Fund Project:Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA050609), the National Natural Science Foundation of China (Grant No. 61274060), and the CAS Interdisciplinary Innovation Team.Received Date:01 November 2016
Accepted Date:18 January 2017
Published Online:05 April 2017
Abstract:CdTe is a promising material for fabricating high-efficient and low-cost thin film solar cell. To achieve high energy conversion efficiency, polycrystalline CdTe films must go through an annealing process in an atmosphere containing chlorine. Numerous researches of the mechanisms of chlorine treatment have been conducted. It is generally believed that chlorine treatment can increase the quantum efficiency of CdTe, cause CdTe grain to recrystallize, and reduce the defect density. In 2014 a research discovered that after chlorine treatment, Cl atoms are segregated at grain boundaries of CdTe and form p-n-p junction, which can separate electrons and holes, thus inhibiting the carrier recombination at grain boundaries. Another first-principle calculation research claimed that Cl atoms form VCd-ClTe complex, which is also named A-center, and provide extra shallow p-energy level to improve shallow p-doping of CdTe. It seems that both segregation and doping of Cl atoms can enhance cell performance.To test whether chlorine doping can contribute to the enhancement of cell performance, in this work we study chlorine doping in CdTe absorption layer by experiment. We deposit chlorine doped CdTe (CdTe:Cl) film by well controlling the chlorine concentration ((1005) ppm) to investigate the effects of Cl doping on device performance. In this work, we also compare the lattice structure and electrical properties of CdTe:Cl films with those of conventional Cl treated CdTe films.The CdTe:Cl film deposited at low temperatures consists of both cubic and hexagonal phases. CdTe:Cl film deposited at high temperature consists of only cubic phase with (111) orientation. Phase structure remains stable after annealing. Serried twins can be observed in all CdTe:Cl rods and the twins each contain only several atom layers. The ultra-thin twins can be found in both as-deposited CdTe:Cl and post-annealing CdTe:Cl. There is neither separate conduction channel of electrons nor that of holes in CdTe:Cl. But for chlorine treated CdTe, grain boundaries are the conduction channels of electrons and holes traveling within grains. The resistivity of the CdTe:Cl film is found to increase drastically, and carrier density reduces to intrinsic state after annealing. The efficiency of CdTe:Cl cell is lower than that of chlorine treated CdTe cell. It seems that non-balanced heavy chlorine doping by magnetron sputtering is bad to CdTe absorption layer.
Keywords: Cl doped CdTe/
Cl treated CdTe/
high-revolution transmission electron microscope/
conductive atomic force microscope
