Annihilation of structural defects in chalcogenide absorber films for high-efficiency solar cells

Roland Mainz*, Ekin Simsek Sanli, Helena Stange, Doron Azulay, Stephan Brunken, Dieter Greiner, Shir Hajaj, Marc D. Heinemann, Christian A. Kaufmann, Manuela Klaus, Quentin M. Ramasse, Humberto Rodriguez-Alvarez, Alfons Weber, Isaac Balberg, Oded Millo, Peter A. Van Aken, Daniel Abou-Ras

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

40 Scopus citations

Abstract

In polycrystalline semiconductor absorbers for thin-film solar cells, structural defects may enhance electron-hole recombination and hence lower the resulting energy conversion efficiency. To be able to efficiently design and optimize fabrication processes that result in high-quality materials, knowledge of the nature of structural defects as well as their formation and annihilation during film growth is essential. Here we show that in co-evaporated Cu(In,Ga)Se2 absorber films the density of defects is strongly influenced by the reaction path and substrate temperature during film growth. A combination of high-resolution electron microscopy, atomic force microscopy, scanning tunneling microscopy, and X-ray diffraction shows that Cu(In,Ga)Se2 absorber films deposited at low temperature without a Cu-rich stage suffer from a high density of-partially electronically active-planar defects in the {112} planes. Real-time X-ray diffraction reveals that these faults are nearly completely annihilated during an intermediate Cu-rich process stage with [Cu]/([In] + [Ga]) > 1. Moreover, correlations between real-time diffraction and fluorescence analysis during Cu-Se deposition reveal that rapid defect annihilation starts shortly before the start of segregation of excess Cu-Se at the surface of the Cu(In,Ga)Se2 film. The presented results hence provide direct insights into the dynamics of the film-quality-improving mechanism.

Original languageAmerican English
Pages (from-to)1818-1827
Number of pages10
JournalEnergy and Environmental Science
Volume9
Issue number5
DOIs
StatePublished - May 2016

Bibliographical note

Publisher Copyright:
© 2016 The Royal Society of Chemistry.

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