Molecular Tuning of Hole‐Selective Interfaces via Phosphonic Acid‐Functionalized Conjugated Polymers for Infrared Photodetectors

Conjugated polymers (CPs) are promising candidates for hole‐transporting layers (HTLs) in next‐generation optoelectronics. However, conventional CP‐based HTLs incorporating alkyl side chains suffer from insufficient interfacial interactions, leading to increased interfacial charge recombination. Here, we report the covalent incorporation of phosphonic groups into a CP‐based HTL through copolymerization with a phosphonate ester monomer, followed by post‐hydrolysis. In organic photodetectors (λ = 808 nm, near‐infrared) and lead sulfide colloidal quantum dot photodetectors (λ = 1550 nm, short‐wave infrared), the optimized devices achieved calculated specific detectivities ( D * white ) of 1.15 × 10 13 and 7.72 × 10 12 cm Hz 0.5 W −1 , respectively, with experimental specific detectivities ( D * exp ) of 1.71 × 10 12 and 1.91 × 10 11 cm Hz 0.5 W −1 . These values are orders of magnitude higher than those of control devices. Structural analysis revealed that the phosphonate ester functionality hindered the formation of face‐on stacking in the CP films, whereas this effect was minimized in the phosphonic acid–functionalized CP. Importantly, the phosphonic acid groups facilitated interlayer interactions through P─OH bonding and intermolecular O─H⋯π and O─H⋯S interactions with the conjugated backbone, enabling enhanced hole extraction and transport from the photoactive layer to the anode.