Persistent photoconductivity effects in printed n-channel organic transistors

Abstract

Persistent photoconductivity of top-gate n-type organic transistors is investigated. The irradiation of green light leads to a negative shift in transistor threshold voltage and an increase in sub-threshold current. These light-induced effects are enhanced when the gate is negatively biased during the light irradiation, and the recovery process is faster at 60 °C than at 25 °C. After storage in dark, full recovery is obtained for a transistor printed with a neat semiconductor, whereas for the device printed with a solution of the same semiconductor mixed with an insulator, only partial recovery is observed after four days at room temperature. Other stress conditions (irradiation with a positive gate bias, irradiation without bias, and bias under dark) do not change the threshold voltage or the sub-threshold current significantly. We attribute this photo phenomenon to holes trapped and released at the dielectric/semiconductor interface and a smaller number of positive fixed charges generated in the bulk of the semiconductor layer.