Please use this identifier to cite or link to this item: https://doi.org/10.21256/zhaw-22628
Publication type: Article in scientific journal
Type of review: Peer review (publication)
Title: When photoluminescence, electroluminescence, and open-circuit voltage diverge : light soaking and halide segregation in perovskite solar cells
Authors: Ebadi Garjan, Firouzeh
Yang, Bowen
Kim, YeonJu
Mohammadpour, Raheleh
Taghavinia, Nima
Hagfeldt, Anders
Tress, Wolfgang
et. al: No
DOI: 10.1039/D1TA02878B
10.21256/zhaw-22628
Published in: Journal of Materials Chemistry A
Volume(Issue): 9
Issue: 24
Page(s): 13967
Pages to: 13978
Issue Date: 4-Jun-2021
Publisher / Ed. Institution: Royal Society of Chemistry
ISSN: 2050-7488
2050-7496
Language: English
Subject (DDC): 621.3: Electrical, communications, control engineering
Abstract: Perovskite solar cells suffer from various instabilities on all time scales. Some of them are driven by light, in particular when employing compounds with mixed halides. Such light soaking effects have been observed in performance changes of solar-cell devices. They have also been spectroscopically investigated in detail on films, where the formation of a low-gap iodine rich phase, seen in a red shift of the PL has been made responsible for a reduced open-circuit voltage. However, studies synchronously examining device performance and its relation to spectroscopy data, are scarce. Here, we perform an in-operandum study, where we investigate changes of open-circuit voltage (Voc) and photocurrent during light soaking and complement it with photo- (PL) and electroluminescence (EL) data on devices, which allow analysis of the Voc-limiting processes using optical and optoelectronic reciprocity relations. We find that changes in the Voc for stable single halide compositions are quantitatively correlated with changes in the PL intensity, showing that the Voc follows changes in the quasi-Fermi level splitting. In contrast, changes in Voc for the mixed halide composition are not correlated to the emergence of the low-gap phase, confirming that this phase is not the sole culprit for a low and instable Voc. Instead, non-radiative voltage losses influenced by mobile ions are dominant in devices containing compositions with high Br content. Interestingly, the low-gap phase contributes less to photocurrent, as seen by a wavelength-dependent PL quenching at short circuit. This observation might be explained by the formation of emissive but partially insulated iodine-rich regions in the film. Such an effect is also possible for single halide systems, when the perovskite composition is not stable, seen in an increase of PL at short circuit during light soaking. This indicates that ion migration in general causes photovoltaically inactive regions, without enhancing non-radiative recombination. EL measurements confirm that Rau’s reciprocity relation between external EL quantum efficiency and Voc cannot readily be applied to absorbers with such different phases.
Perovskite solar cells suffer from various instabilities on all time scales. Some of them are driven by light, in particular when employing compounds with mixed halides. Such light soaking effects have been observed in performance changes of solar-cell devices. They have also been spectroscopically investigated in detail on films, where the formation of a low-gap iodine rich phase, seen in a red shift of the PL has been made responsible for a reduced open-circuit voltage. However, studies synchronously examining device performance and its relation to spectroscopy data, are scarce. Here, we perform an in-operandum study, where we investigate changes of open-circuit voltage (Voc) and photocurrent during light soaking and complement it with photo- (PL) and electroluminescence (EL) data on devices, which allow analysis of the Voc-limiting processes using optical and optoelectronic reciprocity relations. We find that changes in the Voc for stable single halide compositions are quantitatively correlated with changes in the PL intensity, showing that the Voc follows changes in the quasi-Fermi level splitting. In contrast, changes in Voc for the mixed halide composition are not correlated to the emergence of the low-gap phase, confirming that this phase is not the sole culprit for a low and instable Voc. Instead, non-radiative voltage losses influenced by mobile ions are dominant in devices containing compositions with high Br content. Interestingly, the low-gap phase contributes less to photocurrent, as seen by a wavelength-dependent PL quenching at short circuit. This observation might be explained by the formation of emissive but partially insulated iodine-rich regions in the film. Such an effect is also possible for single halide systems, when the perovskite composition is not stable, seen in an increase of PL at short circuit during light soaking. This indicates that ion migration in general causes photovoltaically inactive regions, without enhancing non-radiative recombination. EL measurements confirm that Rau’s reciprocity relation between external EL quantum efficiency and Voc cannot readily be applied to absorbers with such different phases.
URI: https://digitalcollection.zhaw.ch/handle/11475/22628
Fulltext version: Accepted version
License (according to publishing contract): Licence according to publishing contract
Restricted until: 2022-06-05
Departement: School of Engineering
Organisational Unit: Institute of Computational Physics (ICP)
Published as part of the ZHAW project: Modellierung und Charakterisierung von neuartigen optoelektronischen Bauelementen
Appears in collections:Publikationen School of Engineering

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