Berlin 2024 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 21: Heterostructures, Interfaces and Surfaces I
HL 21.1: Talk
Tuesday, March 19, 2024, 09:30–09:45, EW 561
Surface passivation and detrimental heat-induced diffusion effects in RbF-treated Cu(In,Ga)Se2 solar cell absorbers — •Amala Elizabeth1, Sudhir K. Sahoo2, Tim Kodalle3, Thomas D. Kühne2, Christian A. Kaufmann3, Hossein Mirhosseini2, and Harry Mönig1 — 1University of Münster, Münster, Germany — 2University of Paderborn, Paderborn, Germany — 3Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany
Recent efficiency gains by Cu(In,Ga)Se2 (CIGS)-based thin film solar cells (> 23%) are largely attributed to post-deposition treatments (PDTs) using alkali metal compounds like RbF and CsF. Consequently, comprehending the impact of alkali PDTs on the electronic defect physics of these absorber surfaces is crucial for understanding p/n junction formation and further device optimization.
Here we present a combined analytical study of the RbF-CIGS surface using scanning tunneling spectroscopy (STS) and X-ray photoelectron spectroscopy (XPS). STS results reveal the effectiveness of RbF PDT in preventing surface oxidation and consequently passivating electronic defect levels at the absorber surface. Ab-initio density functional theory (DFT) calculations corroborate this passivating effect. However, heat treatment at temperatures as low as 100∘C was found to induce Rb diffusion, leading to increased electronic defect levels at the surface and potential deterioration of the p/n-junction interface. This study emphasizes the dual impact of RbF PDT, with its advantages and potential drawbacks, especially during subsequent device fabrication steps at elevated temperatures.
Keywords: CIGS; RbF post deposition treatments; surface passivation; scanning tunneling spectroscopy; X-ray photoelectron spectroscopy