Synthesis of solution processable ultraviolet sensitive organic molecules and their application in hybrid UV photodetector

Two new solution processable organic molecules based on carbazole and triphenylamine (TPA) substituted fluorene were synthesized by Suzuki coupling reaction. The bandgap of the molecules can be controlled by the 3,6-linkage of the carbazole. The propeller-shaped TPA moieties endow the molecules with good thermal stability and perfect solution processability. Smooth films of both molecules could be readily obtained by spin-coating and n-type ZnO nanoparticles were further incorporated to construct bulk-heterojunction. Under the excitation of 1 mW/cm2 ultraviolet light at 365 nm, devices with those hybrid films as active layers show a relative quick response with photo-to-dark current ratio of about three orders of magnitude. The current decay time (decay to 1% of the value before removing of the light) is less than 200 ms. Moreover, the spectral response of the devices covers 300–400 nm and can be well tuned by the conjugation length of the organic molecules. Those results indicate that the synthesized molecules might be candidates for solution processable low cost UV photodetectors.