Complex Surface Chemistry of Kesterites: Cu/Zn Reordering after Low Temperature Postdeposition Annealing and Its Role in High Performance Devices
Complex Surface Chemistry of Kesterites: Cu/Zn Reordering after Low Temperature Postdeposition Annealing and Its Role in High Performance Devices
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DOI：
10.1021/acs.chemmater.5b01473
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发表时间：
2015-08-11
影响因子：
8.6
通讯作者：
Saucedo, Edgardo
中科院分区：
文献类型：
--
作者：
Neuschitzer, Markus;Sanchez, Yudania;Saucedo, Edgardo
详细的研究解释了低温沉积后退火结合选择性表面蚀刻Cu 2 ZnSnSe 4（CZTSe）为基础的太阳能电池的有益效果。在进行选择性氧化表面蚀刻以去除通常在合成工艺期间形成的ZnSe次级相之后，需要额外的200摄氏度退火步骤以将器件性能从低于3%的功率转换效率提高到最佳情况下的8.3%。这种效率的显著提高可以通过表面化学的变化来解释，这导致通常用于这种吸收体/缓冲层/窗口异质结太阳能电池中的CdS/CZTSe异质结的强烈改善。XPS测量表明，200摄氏度的退火促进了蚀刻的CZTSe吸收体表面相对于CZTSe本体的Cu耗尽和Zn富集。拉曼测量证实了Cu/Zn有序的变化和缺陷密度的增加。此外，TEM显微结构的调查表明，晶界组成的变化，减少其Cu含量后，200摄氏度退火处理。此外，在CdS/CZTSe界面的见解得到了显着量的Cu在CdS缓冲层，这进一步有助于形成的Cu耗尽的表面，似乎在pn-异质结的形成中发挥了重要作用。
A detailed study explaining the beneficial effects of low temperature postdeposition annealing combined with selective surface etchings for Cu2ZnSnSe4 (CZTSe) based solar cells is presented. After performing a selective oxidizing surface etching to remove ZnSe secondary phases typically formed during the synthesis processes an additional 200 degrees C annealing step is necessary to increase device performance from below 3% power conversion efficiency up to 8.3% for the best case. This significant increase in efficiency can be explained by changes in the surface chemistry which results in strong improvement of the CdS/CZTSe heterojunction commonly used in this kind of absorber/buffer/window heterojunction solar cells. XPS measurements reveal that the 200 degrees C annealing promotes a Cu depletion and Zn enrichment of the etched CZTSe absorber surface relative to the CZTSe bulk. Raman measurements confirm a change in Cu/Zn ordering and an increase in defect density. Furthermore, TEM microstructural investigations indicate a change of grain boundaries composition by a reduction of their Cu content after the 200 degrees C annealing treatment. Additionally, insights in the CdS/CZTSe interface are gained showing a significant amount of Cu in the CdS buffer layer which further helps the formation of a Cu-depleted surface and seems to play an important role in the formation of the pn-heterojunction.