p-Type Conjugated Polymers Containing Electron-Deficient Pentacyclic Azepinedione

Area of Science:

• Organic electronics
• Materials science
• Polymer chemistry

Background:

• Bisthienoazepinedione (BTA) is known for high-performance p-type conjugated polymers.
• The ring-extended version, BTTA, is less explored.

Purpose of the Study:

• Synthesize a novel ring-expanded electron-deficient pentacyclic azepinedione (BTTA) building block.
• Investigate copolymers of BTTA with benzodithiophene (BDT) for organic electronic applications.

Main Methods:

• Synthesized BTTA as a key building block.
• Prepared three copolymers of BTTA with differently side-chained BDT units.
• Fabricated and characterized organic field-effect transistors (OFETs) and organic photovoltaic (OPV) devices.

Main Results:

• Polymers showed similar energy levels and absorption but varied film morphologies.
• Best OFET hole mobilities reached 0.027 cm² V⁻¹ s⁻¹ with alkylthienyl side chains on BDT (pBDT-BTTA-2).
• OPV devices achieved 6.78% efficiency with PC71BM and 13.5% with BTP-eC9 acceptor.

Conclusions:

• The electron-deficient BTTA unit is versatile for high-performance p-type polymers.
• Side chain engineering on BDT significantly impacts film morphology and device performance.
• BTTA-based polymers show promising results for organic electronics, comparable to state-of-the-art.