The Nanoscale Structure and Stability of Organic Photovoltaic Blends Processed with Solvent Additives

Area of Science:

• Materials Science
• Organic Electronics
• Nanotechnology

Background:

• Optimizing organic photovoltaic (OPV) performance requires precise control over the nanomorphology of photoactive blends.
• Solvent additives, such as 1,8-diiodooctane (DIO), are used to tune film nanostructure by altering drying dynamics.
• The impact of DIO processing on nonfullerene acceptor (NFA) systems remains less understood compared to fullerene-based systems.

Purpose of the Study:

• To investigate the influence of DIO processing on the nanomorphology and stability of both fullerene-based and NFA-based OPV systems.
• To compare the nanoscale evolution of these systems after fabrication, thermal annealing, and aging.
• To provide insights into the distinct morphological responses of NFA systems to solvent additive processing.

Main Methods:

• Small angle neutron scattering (SANS) was employed to probe the nanomorphology of blend films.
• A deuterated NFA analog (ITIC-d52) was synthesized to enhance neutron scattering contrast in polymer:NFA blends.
• Films were characterized immediately after fabrication, after thermal annealing, and after 1 year of aging.

Main Results:

• DIO processing affects fullerene and NFA-based OPV systems differently.
• NFA-based systems (PBDB-T:ITIC) exhibited more pronounced phase-separated domains compared to fullerene-based systems (PBDB-T:PC71BM).
• Long-term aging (1 year) revealed thermodynamic-induced domain coarsening in both fullerene and NFA systems.

Conclusions:

• Solvent additive processing with DIO leads to distinct nanomorphological outcomes in fullerene versus NFA-based OPVs.
• NFA systems demonstrate greater sensitivity to phase separation during processing.
• Both system types undergo domain coarsening over extended periods, highlighting stability considerations for OPV applications.