Comprehensive understanding of fluorination-performance relationship: The best-performed A-D-A-type acceptors

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Acceptor-donor-acceptor (A-D-A)-type nonfullerene acceptors (NFAs) are crucial for organic solar cells (OSCs).
• Achieving high power conversion efficiency (PCE) in A-D-A acceptors is limited by understanding how to balance charge generation and energy loss.
• Fluorination is a key strategy to tune molecular properties, but its impact on A-D-A acceptor performance in OSCs needs further investigation.

Purpose of the Study:

• To investigate the effect of fluorination on the photoelectric and aggregation properties of A-D-A-type NFAs.
• To elucidate the mechanism behind low energy loss and efficient charge generation in fluorinated A-D-A acceptors.
• To optimize molecular design for enhanced PCE in OSCs.

Main Methods:

• Design and synthesis of a series of A-D-A-type acceptors (ZITI-N-nF, n=2, 4, 6, 8) with varying degrees of fluorination.
• Fabrication and characterization of binary and ternary OSC devices using the synthesized acceptors.
• Analysis of charge-transfer states, energy loss (E_loss), and nonradiative recombination to understand device performance.

Main Results:

• The ZITI-N-6F acceptor demonstrated reduced nonradiative recombination, leading to lower energy loss.
• Devices based on ZITI-N-6F achieved a PCE of 16.11% in binary OSCs and 17.09% in ternary OSCs.
• A certified PCE of 16.6% for ZITI-N-6F-based OSCs was verified, representing the highest reported for A-D-A-type NFAs.

Conclusions:

• Fine-tuning the charge-transfer state through strategic fluorination is effective for reducing energy loss and enhancing charge generation in A-D-A-type NFAs.
• The ZITI-N-6F molecule represents a significant advancement in A-D-A NFA design for high-performance OSCs.
• This study provides valuable insights into the structure-property relationships governing photovoltaic performance in fluorinated NFAs.