Enhanced performance of PbPc photosensitive organic field effect transistors by inserting different-thickness pentacene inducing layers

Abstract

Lead phthalocyanine (PbPc) based photosensitive organic field effect transistors (PhOFETs) with different-thickness pentacene inducing layers (INLs) inserted between SiO2 and PbPc layer were fabricated and characterized. The photoelectric measurements demonstrate that the device with 2-nm-thick pentacene INL exhibits the largest photoresponsivity of 505.75mA/W and maximum photo/dark current ratio of 405.35 in all devices. For this, we give an overall explanation that different-thickness INLs display different continuity and crystallinity and thus produce strong or weak template inducing. Especially, when the INL thickness (δ) is 2nm a quasi-continuous and highly crystalline approximate-monolayer INL forms on SiO2 surface, which may play a strong role of template inducing, thus causing its upper PbPc film to demonstrate the strongest triclinic (300) line and the strongest NIR absorption in series PbPc films. When δ=1nm, pentacene does not form a continuous film. And when δ=5 or 10nm, a continuous multilayer INL with a declined crystallinity due to possible lattice mismatch forms on SiO2 surface and gives a weakened template inducing. Thereby, it can be recognized that inserting a pentacene INL can markedly enhance the performance of single layer PbPc PhOFET and the optimum INL thickness is proved ∼2nm in present conditions.