Direct Imaging of Cl- and Cu-Induced Short-Circuit Efficiency Changes in CdTe Solar Cells
Direct Imaging of Cl- and Cu-Induced Short-Circuit Efficiency Changes in CdTe Solar Cells
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DOI：
10.1002/aenm.201400454
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发表时间：
2014-10-28
影响因子：
27.8
通讯作者：
Pennycook, Stephen J.
中科院分区：
文献类型：
--
作者：
Poplawsky, Jonathan D.;Paudel, Naba R.;Pennycook, Stephen J.
为了实现高效的基于多晶碲化镉（CdTe）的薄膜太阳能电池，碲化镉吸收层必须经过沉积后的氯化镉（CdCl₂）热处理，随后进行铜扩散步骤。为了更好地理解每种处理在改善晶粒、晶界和界面方面的作用，使用截面电子束诱导电流、电子背散射衍射和扫描透射电子显微镜技术对经过和未经过铜扩散以及氯化镉热处理的碲化镉太阳能电池进行了研究。确定了由于这些处理导致短路电流增加和开路电压提高而引起的截面载流子收集分布的变化。此外，还揭示了经过这些处理中的一种或两种之后晶界处载流子收集增加。晶界处电流增加是由于存在一个空间电荷区，其本征载流子收集分布宽度约为350纳米。扫描透射电子显微镜电子能量损失谱显示，处理后晶界处碲（Te）浓度降低，氯（Cl）浓度增加，这导致了反转。每种处理分别提高了电池的整体载流子收集效率，因此，每种处理所实现的益处被证明是相互独立的。
To achieve high-efficiency polycrystalline CdTe-based thin-film solar cells, the CdTe absorbers must go through a post-deposition CdCl2 heat treatment followed by a Cu diffusion step. To better understand the roles of each treatment with regard to improving grains, grain boundaries, and interfaces, CdTe solar cells with and without Cu diffusion and CdCl2 heat treatments are investigated using cross-sectional electron beam induced current, electron backscatter diffraction, and scanning transmission electron microscope techniques. The evolution of the cross-sectional carrier collection profile due to these treatments that cause an increase in short-circuit current and higher open-circuit voltage are identified. Additionally, an increased carrier collection in grain boundaries after either/both of these treatments is revealed. The increased current at the grain boundaries is shown to be due to the presence of a space charge region with an intrinsic carrier collection profile width of approximate to 350 nm. Scanning transmission electron microscope electron-energy loss spectroscopy shows a decreased Te and increased Cl concentration in grain boundaries after treatment, which causes the inversion. Each treatment improves the overall carrier collection efficiency of the cell separately, and, therefore, the benefits realized by each treatment are shown to be independent of each other.