A Narrow-Bandgap n-Type Polymer with an Acceptor-Acceptor Backbone Enabling Efficient All-Polymer Solar Cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Narrow-bandgap polymer semiconductors are critical for organic solar cell development.
• Developing efficient polymer acceptors is key to advancing all-polymer solar cells (all-PSCs).

Purpose of the Study:

• To synthesize and characterize a novel narrow-bandgap polymer acceptor, L14, with an acceptor-acceptor (A-A) backbone.
• To evaluate the performance of L14 in all-polymer solar cells and understand its efficiency-enhancing mechanisms.

Main Methods:

• Copolymerization of a dibrominated fused-ring electron acceptor (FREA) with distannylated bithiophene imide to create the L14 polymer.
• Fabrication and characterization of all-polymer solar cells using the synthesized L14 acceptor.

Main Results:

• The L14 polymer exhibits a narrow bandgap, high absorption coefficient, and low-lying frontier molecular orbital (FMO) levels.
• All-polymer solar cells incorporating L14 achieved a power conversion efficiency of 14.3%.
• Low nonradiative recombination loss (E_loss,nr = 0.22 eV) contributed to maintaining a high open-circuit voltage (V_oc).

Conclusions:

• Narrow-bandgap A-A type polymers are superior for enhancing all-PSC performance.
• The L14 polymer demonstrates excellent potential as a high-performance acceptor for all-PSCs.
• This work provides a pathway for developing advanced polymer acceptors for efficient organic photovoltaics.