Optical analysis of the microstructure of a Mo back contact for Cu(In,Ga)Se2 solar cells and its effects on Mo film properties and Na diffusivity
Optical analysis of the microstructure of a Mo back contact for Cu(In,Ga)Se2 solar cells and its effects on Mo film properties and Na diffusivity
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DOI：
10.1016/j.solmat.2011.02.030
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发表时间：
2011-11
影响因子：
6.9
通讯作者：
J. Yoon;Sunghun Cho;W. Kim;Jong Keuk Park;Y. Baik;T. Lee;T. Seong;J. Jeong
中科院分区：
文献类型：
--
作者：
J. Yoon;Sunghun Cho;W. Kim;Jong Keuk Park;Y. Baik;T. Lee;T. Seong;J. Jeong
研究了在3.3 ~ 10.3mTorr气压范围内沉积的钼（Mo）薄膜的微观结构，并分析了这些微观结构与薄膜性能（残余应力和电阻率）之间的关系。在低沉积压力制度（区域I，低于7 mTorr），在拉伸方向上的残余应力随着压力的增加而增加，并且电阻率逐渐增加，但在高沉积压力（区域II，高于7 mTorr），残余应力降低，并且电阻率更陡峭地增加。这些变化的性能的Mo膜在低压制度是由于晶粒尺寸的变化;载流子迁移率降低，由于增加的晶界（GB）散射和拉伸应力增加，由于增加的原子吸引力在GB。与此相反，钼膜的孔隙率显着增加，在高压制度，所示的可变角光谱椭圆偏振法（VASE）。这些孔中的大多数被认为是存在沿着的Mo膜的晶界，所以它们的存在降低GB的吸引力，从而张应力和增强的载流子散射。二次离子质谱分析显示Mo背接触的高孔隙率加速Na从钠钙玻璃扩散到Cu（In，Ga）Se 2（CIGS）膜中。
The microstructures of molybdenum (Mo) thin films deposited at pressures from 3.3 to 10.3mTorr were characterized, and the relationships between these microstructures and the properties of the films (residual stress and electrical resistivity) were investigated. In the low deposition pressure regime (region I, below 7mTorr), the residual stress in the tensile direction increases with increasing pressure and the electrical resistivity increases gradually, but at high deposition pressures (region II, above 7mTorr) the residual stress is reduced and the resistivity increases more steeply. These variations of the properties of the Mo films in the low pressure regime are due to the variation in grain size; the carrier mobility decreases due to increased grain boundary (GB) scattering and the tensile stress increases due to increased atomic attraction across the GBs. In contrast, the porosity of the Mo films increases significantly in the high pressure regime, as demonstrated with variable angle spectroscopic ellipsometry (VASE). Most of these pores are believed to be present along the grain boundaries of the Mo films, so their presence reduces the GB attraction and thus the tensile stress and enhances the carrier scattering. The high porosity of the Mo back contact was shown with secondary ion mass spectroscopy profiling to accelerate the Na diffusion from soda-lime glass into the Cu(In,Ga)Se2(CIGS) film.