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Photo-degradation in air of spin-coated PC60BM and PC70BM films
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).ORCID iD: 0000-0002-7533-4860
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).ORCID iD: 0000-0001-9337-2249
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).ORCID iD: 0000-0002-1609-8909
2018 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 241, p. 26-30Article in journal (Refereed) Published
Abstract [en]

The fullerene derivatives PC60BM and PC70BM are widely used as electron accepting components in the active layer of polymer solar cells. Here we compare their photochemical stability by exposing thin films of PC60BM and PC70BM to simulated sunlight in ambient air for up to 47 h, and study changes in their UV–vis and FT-IR spectra. We quantify the photo-degradation by tracking the development of oxidation products in the transmission FT-IR spectra. Results indicate that PC60BM photodegrades faster than PC70BM. The rate of photo-oxidation of the thin films is dependent on the rate of oxygen diffusion in to the film and on the photo-oxidation rate of a single molecule. Both factors are dependent on the nature of the fullerene cage. The faster photo-oxidation of PC60BM than of PC70BM is in agreement with its slightly lower density and its higher reactivity. The use of PC70BM in solar cells is advantageous not only because of its absorption spectrum, but also because of its higher stability.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 241, p. 26-30
Keywords [en]
Fullerene derivatives, Photo-oxidation, UV-vis spectroscopy, IR spectroscopy
National Category
Condensed Matter Physics
Research subject
Materials Science
Identifiers
URN: urn:nbn:se:kau:diva-66953DOI: 10.1016/j.synthmet.2018.03.021ISI: 000432504000004OAI: oai:DiVA.org:kau-66953DiVA, id: diva2:1196105
Available from: 2018-04-09 Created: 2018-04-09 Last updated: 2019-11-08Bibliographically approved
In thesis
1. Probing the effects of photodegradation of acceptor materials in polymer solar cells: bulk, surface, and molecular level
Open this publication in new window or tab >>Probing the effects of photodegradation of acceptor materials in polymer solar cells: bulk, surface, and molecular level
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polymer solar cells (PSC) have reached record power conversion efficiencies of over 15%. The operational lifetime of PSCs, however, has to increase for their use in large area outdoor applications. In this work, a set of spectroscopic techniques (UV-vis, FTIR, NEXAFS, XPS) was used to study the impact of exposure to light and air (photo-oxidation) on the photoactive layer and its components. We focused on the electron acceptor components: the fullerene derivatives, PC60BM and PC70BM, and the polymer N2200. A comparative study of photo-oxidized PC60BM and PC70BM thin films by UV-vis and FTIR spectroscopy has shown that both materials undergo similar photochemical transformation, with the process being faster in PC60BM, due to the greater curvature of the C60 cage. Comparing experimental FTIR, XPS and NEXAFS spectra of the photo-oxidized PC60BM thin films with the calculated spectra for a large variety of photo-oxidation products, it was found that dicarbonyl and anhydride groups attach to the C60 cage during photo-oxidation. The study of photo-oxidized TQ1:PC70BM blend films by spectroscopic and J-V measurements shows that deterioration of the charge transport in PC70BM is the major contributor to the device performance degradation. Kelvin Probe measurements demonstrated that the charge transport deterioration was due to upward band bending and gap states being formed on the surface of photo-oxidized PC70BM. The TQ1:PC70BM blends films were further studied by AFM-IR in order to determine the lateral distribution of pristine components, as well as the photo-oxidation products. It was found that anhydride oxidation products of PC70BM are equally distributed over the blend film surface. The PC70BM is replaced with the polymer N2200 in the blend with TQ1. The photostability in air of the blend and its neat components was studied by UV-vis and FTIR spectroscopy. The spectra show that thermal annealing improves the photostability in air of both components.

Abstract [en]

Increase of the global energy demand and the climate change are two factors motivating the study and use of renewable energy sources, such as the solar energy. Organic photovoltaics (OPV) is a technology that uses organic molecules to convert solar energy into electricity. These organic molecules can be kept in ink form, allowing OPV device manufacture via coating, and ultimately roll-to-roll printing techniques, resulting in inexpensive, light weight, portable, and mechanically flexible sources of electricity. OPV devices have reached over 15% in power conversion efficiency, but their operational lifetime has to increase.

In this work, the photostability of the active layer in organic solar cells and its molecular components was studied by a variety of spectroscopy, microscopy and electrical characterization techniques, with focus on the chemical changes that these materials undergo during exposure to light and air. The aim was to determine the relation between materials’ degradation and the device performance degradation.

Place, publisher, year, edition, pages
Karlstads universitet, 2019. p. 59
Series
Karlstad University Studies, ISSN 1403-8099 ; 2019:30
Keywords
photovoltaics, polymer solar cell, conjugated polymers, fullerene, photo-oxidation, spectroscopy
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-75093 (URN)978-91-7867-054-3 (ISBN)978-91-7867-064-2 (ISBN)
Public defence
2019-11-29, 21A 342 Eva Erikssonsalen, 13:15 (English)
Opponent
Supervisors
Available from: 2019-11-05 Created: 2019-10-08 Last updated: 2020-01-28Bibliographically approved

Open Access in DiVA

The full text will be freely available from 2020-04-07 11:29
Available from 2020-04-07 11:29

Other links

Publisher's full texthttps://www.sciencedirect.com/science/article/pii/S0379677918300742

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Blazinic, VanjaEricsson, LeifMuntean, Stela AndreaMoons, Ellen

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