Avancini Enrico, Keller Debora, Carron Romain, Arroyo-Rojas Dasilva Yadira, Erni Rolf, Priebe Agnieszka, Di Napoli Simone, Carrisi Martina, Sozzi Giovanna, Menozzi Roberto, Fu Fan, Buecheler Stephan, Tiwari Ayodhya N
Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Switzerland.
Electron Microscopy Center, Empa-Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Switzerland.
Sci Technol Adv Mater. 2018 Nov 19;19(1):871-882. doi: 10.1080/14686996.2018.1536679. eCollection 2018.
Structural defects such as voids and compositional inhomogeneities may affect the performance of Cu(In,Ga)Se (CIGS) solar cells. We analyzed the morphology and elemental distributions in co-evaporated CIGS thin films at the different stages of the CIGS growth by energy-dispersive x-ray spectroscopy in a transmission electron microscope. Accumulation of Cu-Se phases was found at crevices and at grain boundaries after the Cu-rich intermediate stage of the CIGS deposition sequence. It was found, that voids are caused by Cu out-diffusion from crevices and GBs during the final deposition stage. The Cu inhomogeneities lead to non-uniform diffusivities of In and Ga, resulting in lateral inhomogeneities of the In and Ga distribution. Two and three-dimensional simulations were used to investigate the impact of the inhomogeneities and voids on the solar cell performance. A significant impact of voids was found, indicating that the unpassivated voids reduce the open-circuit voltage and fill factor due to the introduction of free surfaces with high recombination velocities close to the CIGS/CdS junction. We thus suggest that voids, and possibly inhomogeneities, limit the efficiency of solar cells based on three-stage co-evaporated CIGS thin films. Passivation of the voids' internal surface may reduce their detrimental effects.
诸如空洞和成分不均匀性等结构缺陷可能会影响铜铟镓硒（CIGS）太阳能电池的性能。我们通过透射电子显微镜中的能量色散X射线光谱分析了共蒸发CIGS薄膜在CIGS生长不同阶段的形貌和元素分布。在CIGS沉积序列的富铜中间阶段之后，在缝隙和晶界处发现了铜硒相的积累。研究发现，空洞是在最终沉积阶段铜从缝隙和晶界向外扩散造成的。铜的不均匀性导致铟和镓的扩散率不均匀，从而导致铟和镓分布的横向不均匀性。使用二维和三维模拟来研究不均匀性和空洞对太阳能电池性能的影响。发现空洞有显著影响，这表明未钝化的空洞由于在靠近CIGS/CdS结处引入了具有高复合速度的自由表面，从而降低了开路电压和填充因子。因此，我们认为空洞以及可能存在的不均匀性限制了基于三阶段共蒸发CIGS薄膜的太阳能电池的效率。对空洞内表面进行钝化可能会降低其有害影响。
