Re-entrant phase behaviour of organic semiconductors

Area of Science:

• Materials Science
• Physical Chemistry
• Organic Electronics

Background:

• The rapid growth in polymeric and small-molecular acceptors for organic photovoltaics necessitates deeper understanding of material behavior.
• Phase behavior in polymer:small-molecular acceptor blends is critical for optimizing device performance and stability.

Purpose of the Study:

• To investigate the phase behavior of 55 polymer:small-molecular acceptor blends.
• To elucidate the relationship between blend composition, phase behavior, and device characteristics.
• To develop a predictive model for the mixing thermodynamics.

Main Methods:

• Experimental characterization of phase behavior in 55 distinct polymer:small-molecular acceptor blends.
• Analysis of glass transition temperature and its correlation with phase diagrams.
• Development and application of an extended mixing free energy model incorporating configurational entropy and free volume.

Main Results:

• Observed non-trivial phase behavior not explained by conventional mixing theories.
• Identified a strong correlation between phase diagrams and variations in glass transition temperature, indicating the significance of configurational entropy.
• Phase behavior was successfully categorized based on the ratio of monomeric volumes.

Conclusions:

• The developed extended model qualitatively reproduces experimental phase behavior.
• Configurational entropy plays a crucial role in the phase behavior of these blends.
• The model provides a foundation for guiding the development of new organic photovoltaic materials.