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Atomic Layer Deposition of Ternary Compounds on Cu(In,Ga)Se2: An In Situ Quartz Crystal Microbalance Study
ACS Applied Energy Materials ( IF 6.4 ) Pub Date : 2020-06-25 00:00:00 , DOI: 10.1021/acsaem.0c01284
Fredrik Larsson 1 , Lars Stolt 1 , Adam Hultqvist 1 , Marika Edoff 1 , Jan Keller 1 , Tobias Törndahl 1
Affiliation  

For ternary compounds grown by atomic layer deposition (ALD), some compositional variations during the first nanometers of deposition can occur if the initial cycles of the process differ from film-on-film growth. This is problematic for applications that require a precise control of the composition near the interface to the underlying material. One such application is thin-film solar cells, where most emerging buffer layers are ternary compounds. However, such compositional variations can be very difficult to quantify with conventional material characterization methods. A method based on in situ quartz crystal microbalance (QCM) was therefore employed, which allows for detailed studies of the initial growth of ternary compound buffer layers on Cu(In,Ga)Se2 (CIGS) solar cell absorbers, namely, Sn1–xGaxOy and Zn1–xSnxOy. Here, conventional Cr/Au-coated quartz crystals were precoated with a Mo/CIGS thin-film stack before being mounted in an ALD reactor, after which the initial growth on the as-deposited CIGS surfaces was recorded using a QCM monitor. The mass gain for each individual subcycle was extracted and used to estimate compositional depth profiles. It was found that the cation ratio differed for up to the first 3 nm of the deposited film compared to bulk composition for both processes. More specifically, Sn1–xGaxOy was slightly enriched in Ga at the interface (Δx ≈ 10%) and Zn1–xSnxOy was enriched in Sn (Δx ≈ 29%). These compositional variations were suppressed when using RbF-treated CIGS surfaces, which is attributed to a decreased nucleation delay. Similar variations are expected to be present in solar cells fabricated with ternary compound buffer layers, which can potentially influence charge transport and recombination near the absorber/buffer interface. The methodology demonstrated in this study can both improve the understanding of interface formation and allow for an enhanced control of interface properties, in thin-film solar cells and other structures that employ ternary compounds grown by ALD.

中文翻译:

Cu(In,Ga)Se 2上三元化合物的原子层沉积:原位石英晶体微天平研究

对于通过原子层沉积(ALD)生长的三元化合物,如果该过程的初始循环与膜对膜生长不同,则可能会在沉积的第一纳米过程中发生某些成分变化。对于需要精确控制与底层材料的界面附近的组成的应用而言,这是有问题的。一种这样的应用是薄膜太阳能电池,其中大多数新兴的缓冲层是三元化合物。但是,用常规材料表征方法很难对这种成分变化进行量化。因此,采用了一种基于原位石英晶体微天平(QCM)的方法,该方法可以对Cu(In,Ga)Se 2(CIGS)太阳能电池吸收器上的三元化合物缓冲层的初始生长进行详细研究。1- x Ga x O y和Zn 1- x Sn x O y。此处,在将常规的Cr / Au涂层石英晶体预先安装在ALD反应器中之前,先用Mo / CIGS薄膜叠层进行预涂层,然后使用QCM监视器记录沉积态CIGS表面的初始生长。提取每个子循环的质量增益,并将其用于估算成分深度曲线。已发现,与两种方法的本体组成相比,在沉积膜的前3 nm处阳离子比都不同。更具体地说,Sn 1– x Ga x O y在界面处的Ga稍微富集(ΔX ≈10%)和Zn 1- X Sn的X ø ý在Sn中富集(Δ X ≈29%)。当使用经RbF处理的CIGS表面时,这些成分变化得到抑制,这归因于成核延迟的降低。预计在具有三元化合物缓冲层的太阳能电池中会出现类似的变化,这可能会影响电荷在吸收体/缓冲层界面附近的传输和复合。在这项研究中演示的方法不仅可以增进对界面形成的理解,而且可以在采用ALD生长的三元化合物的薄膜太阳能电池和其他结构中增强对界面特性的控制。
更新日期:2020-06-25
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