Appropriate Molecular Interaction Enabling Perfect Balance Between Induced Crystallinity and Phase Separation for...

Area of Science:

• Organic electronics
• Materials science
• Photovoltaics

Background:

• Fluorination is a key strategy for tuning the photophysical properties of organic semiconductors.
• Molecular interactions significantly influence bulk heterojunction (BHJ) morphology and device performance in organic solar cells.
• Understanding how molecular interactions affect BHJ film morphology is crucial for optimizing organic electronic devices.

Purpose of the Study:

• To synthesize a novel fluorinated polymer, PBDB-PSF.
• To investigate the impact of molecular interactions on BHJ morphology using both nonfluorinated (ITIC) and fluorinated (IT-4F) acceptor systems.
• To correlate morphology with the performance of organic solar cells.

Main Methods:

• Synthesis of the fluorinated polymer PBDB-PSF.
• Fabrication and characterization of BHJ films with PBDB-PSF blended with ITIC and IT-4F.
• Morphological analysis of the BHJ films.
• Device performance testing to determine power conversion efficiency (PCE).

Main Results:

• The PBDB-PSF:IT-4F system exhibited enhanced crystallization of IT-4F and ideal phase separation due to F-F interactions, leading to superior charge transport.
• The PBDB-PSF:ITIC system showed poor morphology due to unbalanced molecular interactions.
• The PBDB-PSF:IT-4F based device achieved a high PCE of 13.63%, significantly outperforming the PBDB-PSF:ITIC device (9.84%).

Conclusions:

• Tailoring molecular interactions through strategic fluorination is essential for controlling BHJ micromorphology.
• Fluorine-fluorine interactions can effectively induce desirable crystallization and phase separation in BHJ films.
• Optimized molecular interactions and morphology directly translate to enhanced power conversion efficiency in organic solar cells.