Gate-field dependent photosensitivity of soluble 1,2,4,5-tetra(5 '-hexyl-[2,2 ']terthiophenyl-5-vinyl)-benzene based organic thin film transistors

Abstract

The photoresponsive current-voltage characteristics of organic thin film transistors (OTFTs) have been studied as a function of gate-bias. For the active layer of the OTFTs, soluble 1,2,4,5-tetra(5'-hexyl-[2,2']terthiophenyl-5-vinyl)-benzene materials have been used, and the thickness of the active layers varied. The photosensitivity of the OTFTs was controlled through both gate-bias (V(g)) and incident light power. With increasing incident light power, the photosensitivity decreased during the source-drain current actively varied with V(g) [i.e., at on-state with accumulated hole channel (V(g) < V(onset))], while it increased for V(g) >= V(onset) (at off-state without accumulated hole channel). These variations are caused by two kinds of photocurrent mechanisms: one based on the photovoltaic effect for V(g) < V(onset) and another based on the photoconductive effect for V(g) >= V(onset). The maximum photosensitivity of OTFTs was found to be approximately 40 times higher in the on-state than in the off-state due to the contribution of photovoltaic effect in the on-state. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456498]