π-bridge-engineered naphthalenediimide copolymers for all-polymer photodetectors with high specific detectivity

Abstract

Conjugated acceptor polymers have emerged as promising candidates for all-polymer photodetectors (all-PPDs). However, precise molecular structure modulation remains essential to optimize their optoelectronic properties for specific applications. Recent advances have led to a shift from homopolymers to donor-acceptor (D-A) conjugated copolymers to improve device performance. Notably, dual-acceptor architectures(A1-D-A2-D) have shown potential in extending absorption spectra through synergistic electronic effects. In this study, three naphthalenediimide (NDI)-based acceptor polymers with thienopyrrodione (TPD) as the secondary acceptor moieties were designed and prepared via direct arylation polymerization: P(NDI-TPD) (dual-acceptor), P(NDI-T-TPD) (single thiophene π-bridge), and P(NDI-TT-TPD) (thieno[3,2-b] thiophene π-bridge). Systematic investigations revealed that π-bridge engineering significantly modulates molecular planarity, charge delocalization, and energy level alignment. When blended with donor polymers J71 or PTB7-Th, PTB7-Th:P (NDI-TT-TPD)-based devices exhibited broadest response range (300–800 nm) with a peak responsivity of 238.3 mA W⁻¹ and a maximum specific detectivity of 4.9 × 10¹³ Jones at a bias voltage of −0.1 V. The combination of exceptional linear dynamic range (71.8 dB) and microsecond-scale response speed further validates their potential in real-time imaging systems. This work establishes π-bridge engineering as a powerful strategy for developing high-performance all-PPDs, providing fundamental guidelines for molecular design of conjugated acceptor polymers with tailored optoelectronic properties.