Correlative characterization of co-evaporated Cu2ZnSnSe4 thin-films - CORRKEST

近年来，kesterite结构Cu2ZnSn(S,Se)4化合物半导体作为薄膜太阳能电池的吸收材料得到了广泛的研究。对这些化合物迅速增长的兴趣可归因于其构成原料的低成本和丰富，以及其有益的光电性质（直接带隙和高吸收系数），这与已建立的黄铜矿相似。然而，与带隙相比，kesterite太阳能电池的主要限制之一是它们在开路电压中的大损失，其中造成这种现象的原因尚不清楚。kesterite太阳能电池的电子结构很可能受到二次相的强烈影响。由于kesterite化合物在相图中的存在区非常窄，在制备和加工kesterite薄膜过程中容易形成二次相。然而，二次相的发生与kesterite吸收剂的电子结构之间的明确联系尚未建立。这是因为二次相的表征是非常具有挑战性的。在本项目中，我们计划对共蒸发法制备的Cu2ZnSnSe4薄膜进行相关表征。将应用的分析技术将包括原子探针断层扫描、电子显微镜、光电和阴极发光以及电表征。本项目的主要目的是了解kesterite薄膜的电子结构（带隙、缺陷、复合路径）、体成分和微观结构（次生相、有序-无序转变）之间的关系。通过建立基本的成分-结构-性质关系，我们的目标是为kesterites开发一种材料设计概念，这将支持太阳能电池的知识驱动发展。

Recently, kesterite structured Cu2ZnSn(S,Se)4 compound semiconductors have been intensively investigated as absorber materials for thin-film solar cells. The rapidly growing interest in these compounds can be ascribed to the low cost and abundance of the constituting raw materials as well as their beneficial opto-electronic properties (direct band gap and high absorption coefficients), which are similar to those of the established chalcopyrites. However, one of the main limitations of kesterite solar cells is their large loss in open circuit voltage, compared to the band gap, where the reasons for this phenomenon are unclear. The electronic structure of kesterite solar cells is most likely strongly influenced by secondary phases. Secondary phases can be easily formed during fabrication and processing of kesterite films, as kesterite compounds have very narrow existence regions in phase diagrams. However, a clear link between the occurrence of secondary phases and the electronic structure of kesterite absorbers has not yet been established. This is due to the fact that characterization of secondary phases is highly challenging. In this proposed project, we plan to perform correlative characterization on Cu2ZnSnSe4 films, prepared by co-evaporation. The analytical techniques, which will be applied, will include atom probe tomography, electron microscopy, photo- and cathodoluminescence as well as electrical characterization. The main objective of this project is to understand the correlation between the electronic structure of kesterite thin-films (band gap, defects, recombination paths), the bulk composition and the microstructure (secondary phases, order-disorder transition). By establishing fundamental composition-structure-property relationships, we aim to develop a material design concept for kesterites that will support a knowledge driven development of solar cells.