Application of RHC to Isothermal Crystallization of P3HT:PCBM Blends for Organic Solar Cell Studies

Fatma Demir, Niko Van Den Brande, Sabine Bertho, Guy Van Assche, Dirk Vanderzande, Jean Manca, Bruno Van Mele

Research output: Chapter in Book/Report/Conference proceedingMeeting abstract (Book)

Abstract

Rapid Heating Cooling Calorimetry (RHC), recently developed by TA Instruments, is a fast DSC that contains a micro-sized furnace for operation at high scanning rates of up to 2000°C.min-11. It presents great benefits especially for the investigation of time dependent transitions such as isothermal crystallization. Using the high cooling rates, crystallization during cooling can be avoided and a glassy blend can be achieved. Hence, it becomes possible to crystallize isothermally at temperatures closer to the glass transition temperature (Tg)for materials it was not possible for previously.
In this study, the isothermal crystallization kinetics of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend of a 50 wt% PCBM (1:1) were investigated by means of RHC. P3HT:PCBM blends, whose phase diagram was recently determined2, are the state-of-the-art materials for bulk heterojunction organic solar cells. Attaining the best performance requires a finely dispersed phase morphology, with crystalline P3HT and PCBM structures of 10-nm dimensions. During the production of the solar cells, the solvent-cast P3HT:PCBM blend is annealed at temperatures of typically 100°C to 140°C to create the desired phase morphology and increase the solar cell efficiency. However, if the annealing is too long, the efficiency again deteriorates again as a result of the formation of µm-sized PCBM needles. Recent research showed that the rate of efficiency loss shows a maximum around 125°C. As the annealing and the deterioration of the long-term stability both involve crystallization, the isothermal crystallization process of a P3HT:PCBM 1:1 blend was investigated by RHC.
The crystallization rate was obtained by fitting an Avrami kinetics model onto the evolution of the relative crystallinity versus time measured with RHC. Plotting the rate versus crystallization temperature (Tc) reached from the melt state gives a bimodal bell-shaped curve with maxima at 70°C and 110°C. Crystallization from the glassy state also exhibits a bimodal bell-shaped curve with two maxima, at 80°C and 125°C, and overall a higher crystallization rate (Figure 1). Similar observations were made for homopolymers.

Figure 1. Isothermal crystallization of a P3HT:PCBM 1:1 blend.

References
1) Danley, R. L., P. A. Caulfield & S. R. Aubuchon (2008) American Laboratory, 40, 9-11.
2) Zhao J., Swinnen A., Van Assche G., Manca J., Vanderzande D. & B. Van Mele (2009) Journal of Physical Chemistry B, 113(6) 1587-1591.
3) Supaphol, P. & J.E. Spruiell (2001) Polymer, 42, 699-712
Original languageEnglish
Title of host publicationProceeding of the 10th European Symposium on Thermal Analysis and Calorimetry (ESTAC-2010), August 22-27 (2010), Rotterdam, The Netherlands
Pages91-91
Number of pages1
Publication statusPublished - 26 Aug 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

  • organic solar cells
  • P3HT:PCBM
  • RHC
  • isothermal crystallization

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