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

The conjugated small donor molecule p-DTS­(FBTTh2)2, leading to efficient bulk heterojunction organic photovoltaic devices with PC71BM, shows a eutectic phase behavior in combination with its homocoupled analogue. Rapid heat–cool differential scanning calorimetry allows us to construct the state dia...

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Bibliographic Details
Published in:Journal of physical chemistry. C 2019-09, Vol.123 (36), p.22634-22642
Main Authors: Van den Brande, Niko, Defour, Maxime, Liu, Zhen, Verstappen, Pieter, Nies, Erik, Maes, Wouter, Van Assche, Guy, Van Mele, Bruno
Format: Article
Language:English
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Summary:The conjugated small donor molecule p-DTS­(FBTTh2)2, leading to efficient bulk heterojunction organic photovoltaic devices with PC71BM, 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(FBTTh2)2:homocoupled p-DTS­(FBTTh2)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(FBTTh2)2 shows the lowest crystallinity (order) of all mixtures together with a maximum loss of photovoltaic efficiency.
ISSN:1932-7447
1932-7455
DOI:10.1021/acs.jpcc.9b06336