Morphology-Driven Exciton Diffusion Enhances the Charge Generation in Bilayer Organic Solar Cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Bilayer organic solar cells (b-OSCs) utilizing non-fullerene acceptors (NFAs) now rival bulk heterojunction (BHJ) device efficiencies.
• Key challenges remain in overcoming charge-generation losses within these excitonic systems to further boost performance.

Purpose of the Study:

• To investigate the impact of the solvent additive 1-chloronaphthalene (CN) on the charge generation rate and power conversion efficiency (PCE) of Y6-based b-OSCs.
• To establish a rational design strategy for enhancing b-OSC performance by minimizing energy losses.

Main Methods:

• Incorporation of trace amounts of 1-chloronaphthalene (CN) as a solvent additive.
• Morphological analysis and time-resolved absorption spectroscopy to study exciton diffusion.
• Kinetic Monte Carlo (KMC) simulations to understand molecular packing effects.

Main Results:

• Trace CN addition induces stable, solvent-independent morphology in Y6 acceptor layers.
• Optimized morphology significantly extends exciton diffusion length, particularly with CN-assisted dichloromethane (DCM) processing.
• Reduced charge generation losses were directly linked to morphology-driven exciton transport.

Conclusions:

• 1-chloronaphthalene (CN) serves as an effective additive for improving charge generation and PCE in b-OSCs.
• Exploiting long-range exciton diffusion through rational morphology control is a viable strategy for advancing b-OSC performance.
• The findings provide a pathway for minimizing energy losses in organic solar cell devices.