Ether-Functionalized Ammonium Salts to Enhance Electron Transport in n-Type Conjugated Polymers

Conjugated polymers (CPs) are promising solution-processable semiconductors for fabricating next-generation electronic devices. For the realization of highly performing CP-based electronics, ionic additives have been considered to tune the morphology and charge transport of conjugated polymers. However, achieving high-performance n-type CPs remains challenging because of their limited compatibility with ionic additives. Here, an ether-functionalized ammonium salt (EGBr) was introduced as an additive for the benchmark n-type polymer, N2200, to improve miscibility and molecular ordering. The ether functionality facilitated homogeneous film formation, resulting in an enhanced electron mobility (µ_e) of 1.09 cm² V⁻¹ s⁻¹, compared with 0.510 cm² V⁻¹ s⁻¹ for the alkyl-based additive (HptBr) and 0.272 cm² V⁻¹ s⁻¹ for the control. When employed as an electron-transporting layer in organic photodiodes, EGBr-incorporated N2200 enabled efficient electron extraction and suppressed interfacial recombination, yielding a shot-noise-limited specific detectivity (D^*_shot) of 2.11 × 10¹³ cm Hz^0.5 W⁻¹, outperforming the HptBr-incorporated film (8.31 × 10¹² cm Hz^0.5 W⁻¹) and the control (3.79 × 10¹² cm Hz^0.5 W⁻¹). These results highlight that incorporating ether-functionalized ionic additives is an effective strategy to enhance charge transport in n-type CPs and the performance of organic optoelectronic devices.