Ultra-High Dielectric Acceptor Enables 21% Efficiency and Thickness-Insensitive Organic Solar Cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• The dielectric constant (εr) of non-fullerene acceptors (NFAs) is critical for organic solar cell (OSC) performance, affecting exciton dissociation and charge recombination.
• Current NFAs have low εr (≈3-5), limiting device efficiency due to significant recombination losses.

Purpose of the Study:

• To design and synthesize a novel NFA with an enhanced dielectric constant.
• To investigate the impact of high-εr NFAs on the performance and charge dynamics in ternary OSCs.
• To explore dielectric engineering for improved thickness tolerance in OSC fabrication.

Main Methods:

• Synthesis of a new NFA, L8-BO-FO, by incorporating dimethyl ether units to increase εr.
• Fabrication of ternary OSCs using a blend of PM6:L8-BO with the high-εr L8-BO-FO guest acceptor.
• Characterization of the dielectric properties, exciton dynamics, and charge recombination in the active layer.
• Performance evaluation of the ternary OSCs, including power conversion efficiency (PCE) and thickness dependence.

Main Results:

• The new L8-BO-FO acceptor exhibited a significantly higher εr (7.41) compared to L8-BO (4.57).
• Incorporating L8-BO-FO into the PM6:L8-BO system increased the active layer's εr, accelerated exciton dynamics, and suppressed nonradiative recombination.
• Ternary OSCs achieved a boosted PCE of 21.0% and maintained 19.1% PCE even with a 300 nm active layer thickness.

Conclusions:

• Dielectric engineering using high-εr NFAs is a viable strategy to enhance OSC performance.
• The developed L8-BO-FO acceptor improves charge dynamics and enables excellent thickness tolerance in ternary OSCs.
• This approach offers insights for fabricating high-throughput and scalable OSCs.