Benzothienobenzothiophene/polyimide blend-based organic phototransistors with double-layer gate dielectric

Herein, we report on the double-layer gate dielectric effects on organic phototransistors (OPTs) based on 2,7-dipentyl[1]benzothieno[3,2-b][1]benzothiophene (C5-BTBT)/polyimide (PI) blends as channel materials. The content of C5-BTBT in a blend was varied from 90 to 10 wt.%. We fabricated OPTs with double-layer gate dielectric composed of PVP/pMSSQ (denoted as XD) and SiO2 dielectrics. The introduction of the XD layer enabled shifting of the threshold voltage to more positive values of the gate voltage, eliminated hysteresis in the dark, and suppressed the hysteresis under UV light illumination. In addition to effects of the double-layer gate dielectric, it was found that the best performance of OPTs was achieved with a very low content of C5-BTBT in the blend (20 wt.%). Under UV light intensity of 3 mW cm−2, 20:80 C5-BTBT:PI OPTs exhibited the highest photosensitivity (107) and photoresponsivity (67 A W−1) with negligible hysteresis. Evaluation of the photoresponsivity as a function of light intensity revealed that OPTs maintained the high photosensitivity of 107 even under the weak UV light intensity of 0.11 mW cm−2. The dynamic characteristics of OPTs were affected by the XD dielectric layer, the content of PI and the source-drain voltage. The decay times of the persistent photocurrent (the photo memory) were longer for OPTs with the double-layer gate dielectric, higher content of the PI, and at the low source-drain voltage of −0.1 V. The OPTs have potential application as photo memory elements with low operating source-drain voltage and multilevel programming/controlling of their performance.