Simulation of Transient Photoconduction in Organic p-n Junction Bilayer Photodiodes

The transient photoconducting behavior of organic p/n bilayer photocells has been investigated in cells constructed with the copolymer, poly(3-butylthiophene -co-ethylenedioxythiophene), as p-type material and a perylene diimide (PV) as the n-type material. The decay rate constant of the transient photocurrent observed after pulsed illumination is independent of the applied electric field, light intensity, and temperature. However, the peak photoresponse was strongly affected by these variables. Simulations of the photoresponse revealed that the peak current depends primarily on the carrier mobility (at a given light intensity), whereas the characteristic decay rate is hardly influenced by the mobility, but depends on the carrier lifetime which is chiefly due to trapping by deep levels.