Effect of Alkyl Chain Length on the Bandgap, Ferroelectric, and Photoelectric Properties of Lead‐Based Molecular Ferroelectrics

ABSTRACT 2D molecular ferroelectrics have attracted much attention due to their advantages such as low cost, easy processing, and structural tunability. However, the impacts of alkyl chain length on their bandgap, ferroelectric, and photoelectric properties remain unclear. Herein, we present a novel 2D molecular ferroelectric [C ₆ N ₂ H ₁₈ ]PbI ₄ with a P c polar monoclinic structure, a direct bandgap of 2.30 eV, a room‐temperature ferroelectricity with a maximum polarization ( P _m ) of 3.5 µC cm ⁻² . Remarkable polarization‐enhanced photoelectric performance has been achieved, yielding a maximum V _oc of ∼ 0.72 V and J _sc of ∼ 5.62 µA cm ⁻² . The impacts of chain length of diverse alkylamines spacer cations on bandgap, ferroelectric, and photoelectric of the homologous APbI ₄ system (A for 1,4‐diaminobutane, 1,6‐hexamethylenediamine, and 1,8‐diaminooctane) have been systematically investigated. The elongation of alkyl chain length induces a gradual decline in P _m , while simultaneously expanding the optical bandgap and notably enhancing device stability. This work provides a new perspective for the performance optimization of 2D molecular ferroelectrics toward next‐generation optoelectronic devices.