Voids and compositional inhomogeneities in Cu(In, Ga)Se2 thin films: evolution during growth and impact on solar cell performance. Issue 1 (31st December 2018)

• Record Type: Journal Article
• Authors: 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.
• Is Part Of: Science and technology of advanced materials. Volume 19:Issue 1(2018)
• Page Start: 871
• Page End: 882
• Publication Date: 2018-12-31
• Subjects: Cu(In, Ga)2 -- multistage coevaporation -- STEM/EDX; 50 Energy Materials -- 209 Solar cell / Photovoltaics -- 306 Thin film / Coatings; 503 TEM, STEM, SEM -- 302 Crystallization / Heat treatment / Crystal growth; Materials -- Technological innovations -- Periodicals; 620.112
• DOI: 10.1080/14686996.2018.1536679
• Languages: English
• ISSNs: 1468-6996

Abstract

ABSTRACT: Structural defects such as voids and compositional inhomogeneities may affect the performance of Cu(In, Ga)Se2 (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. Graphical Abstract: