Homocoupling Defects of a Small Donor Molecule for Organic Photovoltaics: Quantification of the Eutectic State Diagram by Rapid Heat–Cool Differential Scanning Calorimetry

Niko Van den Brande, Maxime Defour, Zhen Liu, Pieter Verstappen, Erik Nies, Wouter Maes, Guy Van Assche, Bruno Van Mele

Research output: Contribution to journalArticlepeer-review

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Abstract

The conjugated small donor molecule p-DTS(FBTTh 2) 2, leading to efficient bulk heterojunction organic photovoltaic devices with PC 71BM, shows a eutectic phase behavior in combination with its homocoupled analogue. Rapid heat-cool differential scanning calorimetry allows us to construct the state diagram based on (i) the endset of melting of p-DTS(FBTTh 2) 2:homocoupled p-DTS(FBTTh 2) 2 mixtures of different compositions, and (ii) partial integration of the melting trajectory of these mixtures by calculating the fraction of the molten pure excess phase as a function of temperature. These quantitative experimental results are supported by a theoretical calculation model based on Schröder-van Laar equations extended with an interaction function representing the interactions between the mixture's components in the liquid state. The eutectic composition around 30 wt % of homocoupled p-DTS(FBTTh 2) 2 shows the lowest crystallinity (order) of all mixtures together with a maximum loss of photovoltaic efficiency.

Original languageEnglish
Pages (from-to)22634-22642
JournalJournal of Physical Chemistry C
Volume123
Issue number36
DOIs
Publication statusPublished - 12 Sep 2019

Keywords

  • organic photovoltaic blends
  • thermal analysis
  • Rapid Heat-Cool DSC (RHC)
  • phase diagrams

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