8.78% Efficient All-Polymer Solar Cells Enabled by Polymer Acceptors Based on a B←N Embedded Electron-Deficient Unit

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Efficient all-polymer solar cells (all-PSCs) typically rely on imide or dicyanoethylene acceptors.
• Developing novel electron-deficient units is crucial for advancing all-PSC performance beyond current limitations.

Purpose of the Study:

• To synthesize and characterize a novel electron-deficient unit containing B←N bonds for polymer acceptors.
• To investigate the performance of all-PSCs utilizing polymers derived from this new unit.

Main Methods:

• Synthesis of the BNIDT electron-deficient unit.
• Copolymerization of BNIDT with thiophene and 3,4-difluorothiophene to create BN-T and BN-2fT polymers.
• Fabrication and characterization of all-polymer solar cells using PBDB-T as the donor and BN-2fT as the acceptor.

Main Results:

• The BNIDT unit exhibits desirable properties: good coplanarity, favorable single-crystal structure, narrowed bandgap, downshifted energy levels, and extended absorption.
• The resulting polymers BN-T and BN-2fT show wide absorption spectra (350-800 nm), low-lying energy levels, and ambipolar transistor characteristics.
• All-PSCs utilizing BN-2fT achieved a power conversion efficiency of 8.78%, the highest reported for acceptors not based on imide or dicyanoethylene.

Conclusions:

• The novel BNIDT unit represents a new class of electron-deficient building blocks for high-performance polymer acceptors.
• This work demonstrates the potential of BNIDT-based polymers to achieve efficiencies exceeding 8% in all-PSCs, offering a new strategy for efficient organic photovoltaics.