Regensburg 2022 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 34: Focus Session: Perspectives in Cu(In,Ga)Se 2

HL 34.7: Vortrag

Donnerstag, 8. September 2022, 17:45–18:00, H33

Exact determination of Quasi-Fermi Level splitting from absolute photoluminescence and absorptance spectra — •Sevan Gharabeiki, Taowen Wang, Ajay Singh, Alex Redinger, and Susanne Siebentritt — Department of Physics and Materials Science, University of Luxembourg, 4422 Belvaux, Luxembourg

Photoluminescence (PL) is a powerful tool to investigate the Quasi-Fermi level splitting (QFLS) in absorbers and hence the upper limit of the open-circuit voltage (Voc) in a solar cell. Planck's generalized law and external radiative (ERE) method are the two most common ways to determine the QFLS. Planck's generalized law uses a high energy slope of the PL spectrum and assumes the absorptance (A) to be unity for the photons with energy sufficiently higher than the absorber bandgap. However, in CIGSe solar cells, which employ a graded bandgap, and poly-crystalline perovskite solar cells, the assumption A=1 is no more valid. On the other hand, the ERE method makes use of the radiative bandgap. Many studies consider the PL emission peak position to be the radiative bandgap which is not accurate. Herein, we present a combination of PL and absorptance measurements to accurately determine the QFLS in the CIGSe and methylammonium tin-triiodide Perovskite (MASI) absorbers. Then, we compare our QFLS values from the Plancks generalized law and the ERE method. We emphasize that the radiative bandgap and PL maximum are not the same, and using the PL maximum as a radiative bandgap can result in errors in QFLS extraction.