Bulk photovoltaic effect in ferroelectric liquid crystals comprising of quinquethiophene and lactic ester units

Carrier-transporting ferroelectric liquid crystals consisting of quinquethiophene and lactic ester units were synthesized. One compound exhibited a chiral smectic C (SmC*) phase, and another compound exhibited a chiral smectic crystal phase at room temperature below the SmC* phase. The bulk photovoltaic effect was observed in the polarized chiral smectic crystal phase. The absorption edge was shifted to 570 nm from 500 nm of a terthiophene analogue, due to the extension of the pi-conjugated unit. In the polarized smectic crystal phase doped with PCBM, the open circuit voltage and short circuit current was 0.72 V and 270 mu Acm(-2), respectively. The fill factor was improved to 0.63 and the power conversion efficiency was 0.7% in the PCBM-doped quinquethiophene derivative. The spectral sensitivity was extended to 700 nm, due to the absorption of PCBM as well as compound 1. Since compound 1 exhibits the SmC* phase above the chiral smectic crystal phase, the voltage for the poling treatment was remarkably reduced to 5 V from 40 V in the terthiophene analogue.