Solvent additive effects on small molecule crystallization in bulk heterojunction solar cells probed during spin...

Area of Science:

• Materials Science
• Renewable Energy
• Solid-State Physics

Background:

• Solution processable small molecule (SPSM) bulk heterojunction solar cells offer potential for low-cost renewable energy.
• Power conversion efficiency (PCE) in these devices is often limited by morphology and crystallinity.
• Solvent additive processing is a key strategy to optimize the active layer structure.

Purpose of the Study:

• To investigate the kinetic effects of solvent additives on the structural evolution of SPSM during film formation.
• To understand the relationship between additive-induced structural changes and device performance.
• To elucidate the mechanisms by which additives enhance crystalline quality.

Main Methods:

• In situ grazing incidence wide-angle X-ray scattering (GIWAXS) was employed to monitor crystallite formation kinetics.
• Spin casting was used to fabricate the bulk heterojunction solar cell films.
• Analysis focused on structural evolution during and immediately after the spin-casting process.

Main Results:

• The solvent additive was found to significantly influence the kinetics of crystallite formation.
• Evidence of additive-induced polymorphism in the donor SPSM was observed.
• Enhanced crystalline quality of the donor SPSM was achieved in the presence of the additive.
• The additive impacts the structural evolution in a complex manner.

Conclusions:

• Solvent additive processing is a critical factor in controlling the nanoscale morphology of SPSM solar cells.
• Understanding the kinetics of crystallite formation is essential for optimizing PCE.
• The additive promotes desirable structural properties, leading to improved solar cell performance.