On the relation between thermal transformations and morphological stability of polymer:fullerene solar cells

Guy Van Assche, Jun Zhao, Fatma Demir, Niko Van Den Brande, Sabine Bertho, Dirk Vanderzande

Research output: Chapter in Book/Report/Conference proceedingConference paper

Abstract

High-performance polymer solar cells based on regioregular poly(3-hexyl thiophene) (P3HT, donor) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM, acceptor) represent the current state-of-the-art in organic photovoltaics. Reaching the highest efficiencies for these devices requires an optimum bulk heterojunction morphology, consisting of a co-continuous network with a maximum interface area and a mean domain size of 5-10 nm. Such a morphology can be approached by post-production thermal annealing processes, during which reorganization, aggregation, and further crystallization within the initially amorphous or nanocrystalline deposited films result in the formation of larger well-organized domains. In general, the initial morphology of the deposited blend films is the result of a kinetically frozen phase separation or crystallization. Consequently, both thermodynamic and kinetic parameters are responsible for the morphology obtained. In this contribution, we will present a comprehensive study of the phase behaviour of P3HT/PCBM blends over the whole composition range and compare it to the phase behaviour obtained for other conjugated polymers. These phase diagrams are of key importance to gain a fundamental understanding and control of morphology development in said blends of donor-acceptor materials. Moreover, it should be emphasized that the phase diagram is essential in the understanding of the long-term stability of the blended film morphology and consequently of the photovoltaic performance of the corresponding solar cells. It has in fact been demonstrated that long-term operation of various types of polymer/PCBM solar cells (including P3HT/PCBM) at elevated temperatures results in a significant change of the film morphology and a remarkable decrease of the photovoltaic performance.
In this paper, the use of advanced thermal analysis techniques to obtain the phase diagram for polymer/PCBM blends will be discussed. The use of conventional and modulated temperature differential scanning calorimetry (DSC and MTDSC, respectively), as well as fast-scanning differential scanning calorimetry (RHC) to obtain the transition temperatures and kinetics will be discussed.
Translated title of the contributionOver de relatie tussen thermische transformatis en morfologiesche stabiliteit van polymeer:fullereen zonnecellen
Original languageEnglish
Title of host publicationProceedings TPE10 - Technologies for Polymer Electronics, May 18-20 (2010), Rudolstadt, Germany
PublisherThüringisches Institut für Textil- und Kunststoff-Forschung e.V.
Pages56-61
Number of pages6
ISBN (Print)978-3-939473-66-4
Publication statusPublished - 18 May 2010
EventFinds and Results from the Swedish Cyprus Expedition: A Gender Perspective at the Medelhavsmuseet - Stockholm, Sweden
Duration: 21 Sep 200925 Sep 2009

Conference

ConferenceFinds and Results from the Swedish Cyprus Expedition: A Gender Perspective at the Medelhavsmuseet
CountrySweden
CityStockholm
Period21/09/0925/09/09

Keywords

  • solar cells
  • organic photovoltaics - OPV
  • conducting polymer
  • fullerene
  • modulated temperature DSC - MTDSC
  • Rapid Heat-Cool DSC - RHC
  • advanced thermal analysis
  • phase diagrams
  • morphology

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