Persistent photoconductivity effects in printed n-channel organic transistors

Abstract

Persistent photoconductivity of top-gate n-type organic transistors is investigated, as the irradiation of light leads to a negative shift in transistor threshold voltage and an increase in subthreshold current. These light-induced effects are enhanced when the gate is negatively biased during the light irradiation, and the recovery process is faster at 60C than at 25C. 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. Other stress conditions (irradiation with a positive gate bias, irradiation without bias, and bias under dark) do not change the threshold voltage or the subthreshold current significantly. We attribute this photo phenomenon to the 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.