Developing Wide Bandgap Polymers Based on Sole Benzodithiophene Units for Efficient Polymer Solar Cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Developing efficient and cost-effective materials for polymer solar cells (PSCs) is crucial for renewable energy.
• Benzodithiophene (BDT)-based polymers are promising candidates for PSCs due to their tunable electronic properties.
• Side-chain engineering is a key strategy to optimize polymer structure and performance.

Purpose of the Study:

• To synthesize and investigate novel BDT-based wide band gap polymer donors by incorporating heteroatoms (sulfur, fluorine, chlorine) into conjugated side chains.
• To systematically study the impact of these heteroatoms on the electronic properties, molecular packing, and photovoltaic performance of the polymers.
• To identify an optimal side-chain modification for high-efficiency PSCs.

Main Methods:

• Synthesis of four BDT-based polymers: PBDTT, PBDTS, PBDTF, and PBDTCl, with varying heteroatoms in side chains.
• Fabrication of PSCs using these polymers as donors with Y6 as the electron acceptor.
• Characterization of polymer properties including HOMO levels, absorption, molecular packing, charge transport, and device performance (PCE, V_oc, J_sc, FF).

Main Results:

• Introducing sulfur, fluorine, and chlorine atoms into side chains gradually lowered HOMO levels, leading to increased open-circuit voltage (V_oc) from 0.78 V to 0.84 V.
• Side-chain engineering improved polymer chain interactions, optimized blend morphology, and enhanced absorption and crystallinity.
• The chlorinated polymer, PBDTCl, demonstrated superior performance with a power conversion efficiency (PCE) of 13.46%, V_oc of 0.84 V, J_sc of 23.16 mA cm^-2, and FF of 69.2%.

Conclusions:

• Chlorination of BDT-based polymers is an effective strategy for enhancing PSC performance through improved molecular packing, charge transport, and morphology.
• PBDTCl offers a simple synthetic route and high efficiency, making it a promising material for practical and low-cost PSC applications.
• This work highlights the potential of side-chain engineering in designing high-performance organic photovoltaic materials.