Structural and chemical evolution of the CdS:O window layer during individual CdTe solar cell processing steps
Structural and chemical evolution of the CdS:O window layer during individual CdTe solar cell processing steps
复制标题
各个 CdTe 太阳能电池加工步骤中 CdS:O 窗口层的结构和化学演化
DOI：
10.1016/j.solener.2017.11.051
复制
发表时间：
2018
期刊：
影响因子：
6.7
通讯作者：
Wolden, C.A.
中科院分区：
文献类型：
--
作者：
Abbas, A.;Meysing, D.M.;Reese, M.O.;Barnes, T.M.;Walls, J.M.;Wolden, C.A.
氧化硫化镉（CdS：O）是高性能CdTe异质结太阳电池中常用的n型窗口层。通过反应溅射制备的沉积层是XRD无定形的，具有CdS 0.8O1.2的本体组成。最近的研究表明，该层在器件制造过程中经历了显着的转变，但各个高温处理步骤的作用尚不清楚。在这项工作中，高分辨率透射电子显微镜耦合到元素分析被用来了解的异质结区域的演变，通过个别的高温制造步骤的CdTe沉积，CdCl2激活，和背接触激活。结果表明，在600 °C近距离升华沉积CdTe过程中，CdS：O薄膜发生重结晶，厚度显著减小（约30%）。据观察，在此步骤中，氧偏析，形成双层形态的纳米晶体CdS相邻的氧化锡接触和富氧层相邻的CdTe吸收剂。这种双层结构在400 °C CdCl2处理过程中消失，此时薄膜转变为异质结构，硫酸镉团簇随机分布在整个窗口层中。经CdCl2处理后，窗口层厚度基本不变，但在CdTe与窗口区之间形成了一层厚度约为25 nm的梯度界面层。最后，发现用于激活背接触的快速热处理步骤对异质结区的结构或组成具有可忽略的影响。
Oxygenated cadmium sulfide (CdS:O) is often used as then-type window layer in high-performance CdTe heterojunction solar cells. The as-deposited layer prepared by reactive sputtering is XRD amorphous, with a bulk composition of CdS0.8O1.2. Recently it was shown that this layer undergoes significant transformation during device fabrication, but the roles of the individual high temperature processing steps was unclear. In this work high resolution transmission electron microscopy coupled to elemental analysis was used to understand the evolution of the heterojunction region through the individual high temperature fabrication steps of CdTe deposition, CdCl2activation, and back contact activation. It is found that during CdTe deposition by close spaced sublimation at 600 °C the CdS:O film undergoes recrystallization, accompanied by a significant (∼30%) reduction in thickness. It is observed that oxygen segregates during this step, forming a bi-layer morphology consisting of nanocrystalline CdS adjacent to the tin oxide contact and an oxygen-rich layer adjacent to the CdTe absorber. This bilayer structure is then lost during the 400 °C CdCl2treatment where the film transforms into a heterogeneous structure with cadmium sulfate clusters distributed randomly throughout the window layer. The thickness of window layer remains essentially unchanged after CdCl2treatment, but a ∼25 nm graded interfacial layer between CdTe and the window region is formed. Finally, the rapid thermal processing step used to activate the back contact was found to have a negligible impact on the structure or composition of the heterojunction region.