Photocurrent in the Polyfluorene Copolymer/PTCDI Heterojunction Enhanced by Reabsorption of Fluorescence Emission

Copolyfluorenes are of great interest due to their ability to form thin films with tunable optical and electrical properties. In this paper, copolymers of polyfluorene with electron withdrawing dicyanostilbene and dicyanophenanthrene moieties were synthesized; their thin films were characterized by electron spectroscopy, cyclic voltammetry, electrical, and photoelectrical measurements. The mobility of charge carriers in the copolymers was measured for the first time, with the acceptor components providing balanced electron and hole mobilities of the order of 10⁻⁶ cm²·V⁻¹·s⁻¹. Photodetectors based on the copolymer/PTCDI heterojunction exhibited the photoresponse band extended into the green region due to the absorption of PTCDI and an increased photocurrent in the UV-blue absorption band of the copolymer, which is related to the absorption of photoluminescent emission of the copolymers in PTCDI. The presented approach to improving the performance of a polymer-based photodetector is promising in organic optoelectronics.