Effects of bulk and grain boundary properties of Cu(In,Ga)Se 2 photoabsorbers on the device performance of corresponding solar cells Sinju Thomas 1 , Wolfram Witte 2 , Dimitrios Hariskos 2 , Rico Gutzler 2 , Stefan Paetel 2 , Chang-Yun Song 3 , Heiko Kempa 3 , Nora El-Ganainy 4 , Daniel Abou-Ras 1 1 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany 2 Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Meitnerstr. 1, 70563 Stuttgart, Germany 3 Martin-Luther-Universität Halle-Wittenberg, Institut für Physik, Fachgruppe Photovoltaik, von-Danckelmann-Platz 3, 06120 Halle (Saale) 4 Berliner Hochschule für Technik in Berlin Cu(In,Ga)Se 2 (CIGSe) thin-film solar cells are based on a polycrystalline absorber material which is a solid solution of CuInSe 2 and CuGaSe 2 . The bandgap energy ( E g ) of the CIGSe photoabsorber can be tuned by varying the [Ga]/([Ga]+[In]) (GGI) ratio [1][2] which is beneficial for various applications in tandem devices, e.g., by using CIGSe absorber layers as top or bottom cells [3][4]. The highest reported device efficiency is 23.6 %[5]. In the present work, we investigate the various material properties of five CIGSe based thin-film solar cells with GGI of 0.13, 0.34, 0.51, 0.67 and 0.83. The effect of GGI variation on the various material properties of the absorber such as the microstructure, luminescence distribution, recombination velocity of electrons ( S GB,0 ) at the grain boundaries (GB), the effective lifetime of the electrons ( π eff ), the broadening of the absorption edge ( σ g ), the Urbach energy ( E U ) is studied in detail. Finally, we relate the overall impact of these material on the open-circuit voltage ( V OC ) of the solar cell. The present work suggests further investigations on an alternative approach of silver alloying in combination with high GGI, in order to optimize the grain size ( d grain ), π eff and Ga/In gradients and thereby improve the V OC [6]. References 1. Hörig W, Neumann H, Sobotta H, Schumann B, Kühn G. The optical properties of CuInSe 2 thin films. Thin Solid Films , 1978 ;48(1):67–72.Hörig W, H. Neumann H, B. Schumann, G. Kühn. Optical Properties of CuGaSe 2 near and above the Fundamental Absorption Edge. Status Solidi B, 1978 , 85, 57-61. 2. Feurer T, Carron R, Torres Sevilla G, Fu F, Pisoni S, Romanyuk YE, et al. Efficiency Improvement of Near-Stoichiometric CuInSe 2 Solar Cells for Application in Tandem Devices. Adv Energy Mater , 2019 , 9, 2. 3. Jošt M, Köhnen E, Al-Ashouri A, Bertram T, Tomšič Š, Magomedov A, et al. Perovskite/CIGS Tandem Solar Cells: From Certified 24.2% toward 30% and beyond. ACS Energy Lett , 2022 ;7(4):1298–307.https://www.nrel.gov/pv/cell-efficiency.html, referred on 07.07.2023 4. Edoff M,Jarmar T,Nilsson NS, et al.High Voc in (Cu,Ag)(In,Ga)Se 2 solar cells. IEEE J. Photovoltaics . 2017 ;7(6):1789-1794.
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