Phase Behavior of Amorphous/Semicrystalline Conjugated Polymer Blends.

Area of Science:

• Materials Science
• Polymer Science
• Organic Electronics

Background:

• Conjugated polymer blends are essential for organic electronics, particularly in all-polymer solar cells.
• Understanding the phase behavior of these blends is critical for controlling morphology and device performance.
• Immiscibility in polymer blends often arises from unfavorable enthalpic and entropic contributions to mixing.

Purpose of the Study:

• To investigate the phase behavior of amorphous/semicrystalline conjugated polymer blends.
• To determine the miscibility and thermodynamic parameters of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) and poly{(N,N'-bis(2-octyldodecyl)naphthalene -1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) blends.
• To correlate the solid-liquid phase transitions with structural changes.

Main Methods:

• Thermal analysis (Differential Scanning Calorimetry) to observe melting and crystallization behavior.
• X-ray diffraction (XRD) to analyze the structural properties and intermolecular interactions (π-π stacking).
• Estimation of the Flory-Huggins interaction parameter (χ) to quantify miscibility.

Main Results:

• The PCPDTBT/P(NDI2OD-T2) blend was found to be immiscible, with an estimated Flory-Huggins interaction parameter (χ) of 1.26.
• Increasing PCPDTBT content led to a depression in the melting and crystallization points of the blend.
• XRD patterns indicated a reduction in π-π interactions within P(NDI2OD-T2) lamellae upon the addition of PCPDTBT.

Conclusions:

• The study confirms the immiscibility of the investigated amorphous/semicrystalline conjugated polymer blend.
• Phase behavior and structural changes are directly linked, providing insights into blend morphology.
• Understanding these correlations is vital for designing high-performance active layers in all-polymer solar cells, though nonequilibrium kinetics also play a significant role.