Crystallization driven boost in fill factor and stability in additive-free organic solar cells

Area of Science:

• Materials Science
• Renewable Energy
• Organic Electronics

Background:

• Controlling morphology in bulk-heterojunction solar cells is crucial for high performance.
• Non-fullerene acceptors offer potential but require optimized processing for miscibility and nanoscale separation.
• The impact of post-processing on polymer/non-fullerene acceptor solar cells remains largely unexplored.

Purpose of the Study:

• To systematically compare thermal annealing (TA), vacuum drying (VD), and solvent vapor annealing (SVA) as post-processing techniques.
• To evaluate the effects of these treatments on device performance, morphology, and optoelectronic properties.
• To understand the role of post-processing in achieving efficient and stable additive-free organic solar cells.

Main Methods:

• Fabrication of bulk-heterojunction solar cells using TPD-3F polymer and IT-4F non-fullerene acceptor.
• Application of different post-processing techniques: thermal annealing (TA), vacuum drying (VD), and solvent vapor annealing (SVA).
• Characterization of device performance, morphology (GIWAXS), optical, and electrical properties.

Main Results:

• Optimized SVA treatment yielded power conversion efficiencies near 14% with a 76% fill factor and improved short-circuit currents.
• SVA treatment enhanced device stability under illumination and ambient conditions.
• GIWAXS revealed SVA induced better phase separation and increased acceptor crystallinity, leading to higher photocurrents and efficient charge collection.

Conclusions:

• Post-processing strategies, particularly SVA, are vital for optimizing organic solar cell performance and stability.
• SVA effectively controls morphology and crystallinity, crucial for efficient exciton dissociation and charge transport.
• This study highlights the potential of additive-free organic solar cells through strategic post-processing techniques.