Binary Blends of Polyimide and Benzothienobenzothiophene for High‐Performance Solution‐Processed Organic Phototransistors

Abstract A novel, soluble, and strong electron withdrawing polyimide (PI), and its first use to modulate photoelectrical characteristics of organic thin film phototransistors (OPTs), are reported. The PI with strong electron‐withdrawing repeating units is solution blended with UV‐responsive organic semiconductor 2,7‐dipentyl[1]benzothieno[3,2‐b][1]benzothiophene (C5‐BTBT). Photoelectrical properties of OPTs are affected by content but not molecular weight of PI in the blends, which is attributed to strong charge trapping at the interface. 10 wt% PI only in the blends can completely suppress the hysteresis under UV light and increase the drain photocurrent by more than six orders of magnitude in the subthreshold region. All the blend‐based OPTs show excellent operational stability in air and high sensitivity to UV light at a low intensity (0.12 mW cm −2 ). I phc / I D and photosensitivity were 10 6 and 429 A W −1 , respectively, for 70:30 PI1:C5‐BTBT blend. All the blend‐based OPTs have response times of ≈1 s and decay times (UV off) of 149 s, which are 16 times faster and 2 times slower than the control C5‐BTBT OPT. Density functional theory calculations is used to understand the mechanisms. This work demonstrates that the PI/C5‐BTBT blends represent a very promising system for high‐performance OPT devices.