A Dithienopyrazine-Based Wide Band Gap Polymer Donor for Efficient Organic Solar Cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• High-performance organic solar cells (OSCs) require wide band gap polymer donors.
• Developing novel electron-accepting (A) units is crucial for donor material design.

Purpose of the Study:

• To synthesize and characterize novel donor-acceptor (D-A) type copolymers using a new dithienopyrazine (DTPz) electron-accepting unit.
• To evaluate the performance of these copolymers in OSC devices, particularly comparing benzodifuran (BDF) and benzodithiophene (BDT) as electron-donating (D) units.

Main Methods:

• Synthesis of D-A type copolymers DTPz-1 (using BDT) and DTPz-2 (using BDF).
• Fabrication and characterization of OSC devices using these polymers with nonfullerene acceptors (NFAs) like L8-BO.
• Analysis of energy levels, morphology, molecular packing, and charge mobility.

Main Results:

• DTPz-2 demonstrated superior properties including cascade energy levels with L8-BO, optimized phase separation, enhanced molecular packing, and high charge mobility compared to DTPz-1.
• OSC devices based on DTPz-2/L8-BO achieved a power conversion efficiency (PCE) of 15.03%, significantly outperforming DTPz-1/L8-BO devices (8.14% PCE).

Conclusions:

• The dithienopyrazine (DTPz) unit is a viable building block for high-efficiency D-A type polymer donors.
• Benzodifuran (BDF) may be a more suitable electron-donating unit than benzodithiophene (BDT) for specific D-A type photovoltaic donor designs, leading to improved OSC performance.