Ferroelectric Photovoltaic Effect in the Ordered Smectic Phases of Chiral π-Conjugated Liquid Crystals: Improved Current-Voltage Characteristics by Efficient Fixation of Polar Structure

Abstract

We synthesized four liquid-crystalline (LC) compounds with extended π-conjugation, incorporating a chiral branched-alkoxy chain. These compounds displayed ferroelectric chiral smectic C (SmC*) and ordered smectic phases. The carrier transport properties in the LC phases were characterized using the time-of-flight (TOF) method. Although all four chiral phenylterthiophene derivatives exhibited nondispersive hole conduction in the SmC* phases, nondispersive transient curves in the ordered smectic phases were limited. Notably, clear nondispersive photocurrent decays were observed in the ordered smectic phase of an LC compound containing an (R)-3-octyloxy moiety as the chiral unit. This compound achieved hole mobility of 4 × 10−3 cm2 V−1 s−1 in the ordered phase at 114 °C. The polar structure induced by poling treatment in the ferroelectric SmC* phase of the chiral LC compound was successfully stabilized with a lower electric field than previously reported systems. We confirmed the presence of the ferroelectric bulk photovoltaic effect in the polarized structure of the chiral-ordered smectic phase. Furthermore, we observed an enhancement in the output performance for the bulk photovoltaic effect due to the efficient stabilization of the polar structure.