Laser-Induced Morphology Change Based on Small Molecular Model Compounds Photo-Detector

Abstract

Three small molecules furnished with a planar core, (5,6-bis(octyloxy) benzo[c][1,2,5] thiadiazole-4,7-diyl)bis(thiophene-5,2-diyl), and two wings, thieno [3,2-b]indole or carbazoles, were synthesized and used as sensing layer to make photo-detectors. The devices can detect photons at a wavelength band of 300–700 nm and exhibit a sensitive photo-response under on/off modulation. Near UV (405 nm) and visible (532 nm) laser beam were the light source in this work. The corrected responsivity reached up to 498 mA W-1 at 532 nm and 411 mA W-1 at 405 nm. Laser induced photo-current escalation was observed and investigated. For longer molecules, the photo-current was easy to be constant than the shorter reference counterpart. This special photo response mechanism was studied by alternating current impedance spectroscopy (IS) measurements and X-ray diffraction (XRD) exprements. Possible relations between molecular weight and various figures of merit for photo detectors were discussed.