Towards high performance near infrared sensitive multilayer organic phototransistors: effects of the acceptor and its position

Due to its strong optical absorption in the near infrared (NIR) region, lead phthalocyanine (PbPc) is frequently used as the photoactive material in NIR sensitive organic phototransistors (OPTs). Limited by the low charge carrier mobility of NIR sensitive organic semiconductors, the active part of NIR OPTs adopts generally multilayer or multicomponent structure consisting of electron donor, electron acceptor and charge transporting molecules. Here, we investigate the effect of acceptor locations in the active structure on the performances of NIR phototransistors with PbPc as the photoactive electron donor. The performances of OPTs with C-60 layer lying on the top of PbPc (Si/SiO2/pentacene/PbPc/C-60/Au (source and drain electrode, S&D)), above PbPc and Au S&D (Si/SiO2/pentacene/PbPc/Au (S&D)/C-60)), and in the form of bulk-heterojunction with PbPc (Si/SiO2/pentacene/PbPc:C-60/Au (S&D)) were comparatively studied. The results show that the device with pentacene/PbPc:C-60 exhibits the best performance among them. At an incident light intensity of 0.08 mW cm(-2), a high photoresponsivity of 44.35 A W-1, and specific detectivity of 1.08 x 10(12) Jones are achieved.