A Narrow-Bandgap n-Type Polymer Semiconductor Enabling Efficient All-Polymer Solar Cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• High-performance all-polymer solar cells (all-PSCs) often rely on imide-functionalized polymers as n-type acceptors, which typically exhibit medium bandgaps.
• Existing polymer acceptors face limitations such as steric hindrance and suboptimal optoelectronic properties, hindering further advancements in all-PSC technology.

Purpose of the Study:

• To develop a novel narrow-bandgap polymer acceptor for all-PSCs that overcomes the limitations of current imide-based materials.
• To investigate the optoelectronic properties and performance of a new polymer, poly(5,6-dicyano-2,1,3-benzothiadiazole-alt-indacenodithiophene) (DCNBT-IDT), as an n-type acceptor in all-PSCs.

Main Methods:

• Synthesis of a novel narrow-bandgap polymer, DCNBT-IDT, utilizing a dicyanobenzothiadiazole unit without an imide group.
• Characterization of DCNBT-IDT's optoelectronic properties, including bandgap and absorption coefficient, and comparison with benchmark materials like N2200.
• Fabrication and performance evaluation of all-PSCs using DCNBT-IDT as the n-type acceptor blended with a wide-bandgap polymer donor.

Main Results:

• DCNBT-IDT exhibits a narrow bandgap of 1.43 eV and a high absorption coefficient (6.15 × 10^4 cm^-1), surpassing existing polymer acceptors.
• All-PSCs based on DCNBT-IDT achieved a power conversion efficiency (PCE) of 8.32% with a low energy loss of 0.53 eV and extended photoresponse up to 870 nm.
• The DCNBT-IDT based all-PSCs significantly outperformed N2200 (6.13% PCE) and NDI-IDT (2.19% PCE).

Conclusions:

• The novel DCNBT-IDT polymer demonstrates excellent n-type characteristics and improved optoelectronic properties, breaking previous material limitations in all-PSCs.
• This development paves the way for next-generation polymer acceptors with enhanced performance, offering a promising future for all-polymer solar cell technology.