Revealing the Origin of the Beneficial Effect of Cesium in Highly Efficient Cu(In,Ga)Se 2 Solar Cells

Publication date: Available online 17 February 2020Source: Nano EnergyAuthor(s): Philipp Schöppe, Sven Schönherr, Manjusha Chugh, Hossein Mirhosseini, Philip Jackson, Roland Wuerz, Maurizio Ritzer, Andreas Johannes, Gema Martínez-Criado, Wolfgang Wisniewski, Torsten Schwarz, Christian T. Plass, Martin Hafermann, Thomas D. Kühne, Claudia S. Schnohr, Carsten RonningAbstractThe record conversion efficiency of thin-film solar cells based on Cu(In,Ga)Se2 (CIGS) absorbers has exceeded 23 %. Such a high performance is currently only attainable by the incorporation of heavy alkali metals like Cs into the absorber through an alkali fluoride post-deposition treatment (PDT). As the effect of the incorporated heavy alkali metals is under discussion, we investigated the local composition and microstructure of high efficiency CIGS solar cells via various high-resolution techniques in a combinatory approach. An accumulation of Cs is clearly detected at the p-n junction along with variations in the local CIGS composition, showing the formation of a beneficial secondary phase with a laterally inhomogeneous distribution. Additionally, Cs accumulations were detected at grain boundaries with a random misorientation of the adjacent grains where a reduced Cu concentration and increased In and Se concentrations are detected. No accumulation was found at Σ3 twin boundaries as well as the grain interior. These experimental findings are in excellent agreement with complementary ab-initio calculat...
Source: Nano Energy - Category: Nanotechnology Source Type: research