Structural characterization of off-stoichiometric kesterite-type Cu2ZnGeSe4 compound semiconductors: from cation distribution to intrinsic point defect density†,CrystEngComm

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Structural characterization of off-stoichiometric kesterite-type Cu2ZnGeSe4 compound semiconductors: from cation distribution to intrinsic point defect density†
CrystEngComm ( IF 2.6 ) Pub Date : 2018-01-22 00:00:00 , DOI: 10.1039/c7ce02090b
R. Gunder _{1,

2,

3,

4} , J. A. Márquez-Prieto _{1,

2,

3,

4} , G. Gurieva _{1,

2,

3,

4} , T. Unold _{1,

2,

3,

4} , S. Schorr _{1,

2,

3,

4,

5}

Affiliation

The substitution of Ge⁴⁺ for Sn⁴⁺ in Cu₂ZnSn(S,Se)₄ (CZTSSe) kesterite-type absorber layers for thin film solar cells has been proven to enhance the opto-electronic properties of the material. By cationic substitution, in general, the optical bandgap can be more readily designed for the purpose of bandgap engineering, and the substitution of Sn⁴⁺ by Ge⁴⁺, in particular, widens the optical bandgap such that it can be employed for both photovoltaics and solar fuel quarrying by photocatalytic water splitting. This work is an experimental study of intrinsic point defects in off-stoichiometric kesterite-type Cu₂ZnGeSe₄ (CZGSe) by means of neutron powder diffraction. We revealed the existence of copper vacancies (V_Cu), various cation antisite defects (Cu_Zn, Zn_Cu, Zn_Ge, Cu_Ge) as well as interstitials (Cu_i, Zn_i) in a wide range of off-stoichiometric polycrystalline materials synthesized by solid state reaction. In addition to the off-stoichiometry-type specific defects, Cu/Zn disorder is always present in the kesterite-type CZGSe phase. While compositional changes are clearly reflected by the tetragonal deformation c/2a, the lattice parameters a and c seem differently responding to point defect types and concentration variations, respectively. The Cu_Ge antisite defect which is known to greatly deteriorate the opto-electronic properties exists only in Cu-rich CZGSe, but appears already in CZGSe with Cu/(Zn + Ge) ≈ 1. Furthermore, we showed by diffuse reflectance hyperspectral imaging a widening of the energy bandgap in off-stoichiometric kesterite-type CZGSe with decreasing Cu/(Zn + Ge).

中文翻译：

非化学计量的钾盐沸石型Cu ₂ ZnGeSe ₄化合物半导体的结构表征：从阳离子分布到本征点缺陷密度†

业已证明，在薄膜太阳能电池的Cu ₂ ZnSn（S，Se）₄（CZTSSe）硅藻土型吸收层中用Ge ⁴⁺替代Sn ⁴⁺可以增强材料的光电性能。通常，通过阳离子取代，可以更容易地设计用于带隙工程的光学带隙，并且特别地，通过Ge ⁴⁺替代Sn ⁴⁺可以扩大光学带隙，从而可以将其用于两种光伏电池中。以及通过光催化水分解进行的太阳能燃料采石。这项工作是对非化学计量的钾盐沸石型Cu ₂ ZnGeSe ₄的本征点缺陷进行的实验研究。（CZGSe）通过中子粉末衍射。我们揭示了在许多非化学计量的多晶材料中存在铜空位（V _Cu），各种阳离子反位缺陷（Cu _Zn，Zn _Cu，Zn _Ge，Cu _Ge）以及间隙（Cu _i，Zn _i）通过固相反应合成。除了化学计量比类型的特定缺陷外，在钾长石型CZGSe相中始终存在Cu / Zn无序。虽然四方形变形c / 2 a清楚地反映了成分变化，但晶格参数a和c似乎分别对点缺陷类型和浓度变化的响应不同。已知会大大降低光电性能的Cu _Ge反位缺陷仅存在于富含Cu的CZGSe中，但已经出现在具有Cu /（Zn + Ge）≈1的CZGSe中。 Cu /（Zn + Ge）降低时，化学计量失配的钾长石型CZGSe的能带隙变宽。

更新日期：2018-01-22

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