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Electrical properties of CdTe single crystals, defects and their correlation to solar cell performance

机译：CdTe单晶的电学性质，缺陷及其与太阳能电池性能的关系

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摘要

CdTe-based thin film photovoltaics constitute a major part of the world's solar energy supply. However, its efficiency, in particular the open circuit voltage (VOC), has remained low due to material qualities such as short minority carrier lifetime and low acceptor density (NA). The defects in CdTe play a critical role in impacting electrical properties of crystals and related device performance. In this thesis, a systematic study was performed to investigate correlating key material properties of CdTe and device performance.;Eleven CdTe boules or crystals were grown using vertical Bridgman method including undoped, phosphorous-doped, and arsenic-doped. Overall, single crystals showed high purity, high lifetime, and improved NA compared to typical CdTe thin-films reported in literatures. The lifetimes are as high as ∼300 ns in undoped single crystals and 5-50 ns in P-doped single crystals. We demonstrated high acceptor density, in the range of mid-10 16 to low-1017 cm-3, with relatively high bulk minority carrier lifetimes of ∼20-50 ns, which translated into exceptional device performance. Device research at WSU showed device performances were strongly related to material properties. The best performance resulted from the P-doped material, which has the highest NA, lowest resistivity and relatively high lifetime. The device work performed in collaboration with the National Renewable Energy Laboratory (NREL) resulted in cell performance with VOC >1000 mV from P-doped crystals, owing to superior material quality. None of the device fabrication processes on single crystals used CdCl2 treatment.;Defects in CdTe were characterized by thermoelectric-effect spectroscopy (TEES) and studied systematically. Comparative TEES analysis on different types of crystals reveals that around 7-8 defects were observed in all types of crystals which were attributed to native defects. Although relatively high NA was obtained from p-type doped growths, it was observed in crystals from all five P-doped and two As-doped growths that the NA NA was several orders of magnitude less than the dopant concentration, indicating strong self-compensation. The compensations appear to be linked to self-compensating donors and/or defect complexes with cadmium vacancies (VCd). Formation of secondary phases such as Cd 3P2 seems to be responsible for the compensation as well in P-doped growth.
机译：基于CdTe的薄膜光伏电池构成了世界太阳能供应的主要部分。然而，由于诸如短的少数载流子寿命和低的受体密度（NA）之类的材料质量，其效率，特别是开路电压（VOC）一直保持较低。 CdTe中的缺陷在影响晶体的电性能和相关器件性能方面起着至关重要的作用。本文对CdTe的关键材料性能与器件性能之间的关系进行了系统的研究。采用垂直Bridgman方法生长了11种CdTe球团或晶体，包括未掺杂，磷掺杂和砷掺杂。总体而言，与文献中报道的典型CdTe薄膜相比，单晶显示出高纯度，高寿命和改进的NA。未掺杂的单晶的寿命高达〜300 ns，而掺P的单晶的寿命则高达5-50 ns。我们展示了高的受体密度，介于10 16 cm3至低的1017 cm-3之间，具有相对较高的体积少数载流子寿命，约为20-50 ns，这转化为出色的器件性能。 WSU的设备研究表明，设备性能与材料性能密切相关。最佳性能来自P掺杂材料，该材料具有最高的NA，最低的电阻率和相对较高的使用寿命。与美国国家可再生能源实验室（NREL）合作进行的设备工作，由于具有优异的材料质量，因此P掺杂晶体的VOC> 1000 mV时，电池性能得以提高。在单晶上的器件制造工艺均未使用CdCl2处理。CdTe中的缺陷已通过热电效应光谱（TEES）进行了表征并进行了系统的研究。对不同类型晶体的比较TEES分析表明，在所有类型的晶体中均观察到大约7-8个缺陷，这归因于天然缺陷。尽管从p型掺杂生长获得了相对较高的NA，但在所有五个P掺杂和两个As掺杂生长的晶体中都观察到，NA NA比掺杂浓度小几个数量级，表明强的自补偿。补偿似乎与自我补偿的供体和/或具有镉空位（VCd）的缺陷复合物有关。诸如Cd 3P2的次生相的形成似乎也与P掺杂生长中的补偿有关。

著录项

  • 作者

    Tuerxunjiang, Abulikemu.;

  • 作者单位

    Washington State University.;

  • 授予单位 Washington State University.;
  • 学科 Materials science.;Energy.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 158 p.
  • 总页数 158
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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