Measurement of the exciton diffusion length in discotic columnar liquid crystals: Comparison between homeotropically oriented and non-oriented samples

This Letter reports the determination of the singlet exciton diffusion length (LD) for a thermotropic discotic columnar liquid crystal (CLC) in both non-oriented and homeotropically oriented (columns perpendicular to the substrate) samples. Experimental results based on photoluminescence measurements indicate that LD is only slightly dependent on the liquid crystal orientation. Conversely, studies of ITO/CLC (50 nm)/Al Schottky-type devices formed by non-oriented and oriented liquid–crystalline films show an increase in the photocurrent by a factor of 16, due to the homeotropic alignment. This improvement is attributed to both increased light absorption and charge-carrier mobility.