Enhanced performance in doped micro-nano porous organic thin-film transistors

Molecular doping, as an effective technique for controlling the electrical property of organic semiconductors (OSCs) by introducing additional charges, has been proven to adjust important device parameters in organic thin-film transistors (OTFTs). Doping highly crystalline OSCs without disrupting structural order is a crucial challenge, as it significantly affects the charge carrier mobility. Here, we demonstrate a molecular doping method without disrupting the molecular ordering to improve the charge carrier mobility of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) based OTFTs via a simple thermal spin-coating method. The key is to introduce micro-nano pores into C8-BTBT thin-film for channel doping, which is achieved by mixing with the unsubstituted BTBT as it can be easily removed from the thin-film through an ordinary annealing process. Micro-nano pores allow the dopant molecules (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, F4-TCNQ) to access the conductive channel of OTFT, which is beneficial for charge injection. Indeed, we further discover that F4-TCNQ doped porous C8-BTBT thin-films exhibit better charge mobility than those of neat and F4-TCNQ doped C8-BTBT films in OTFTs. This work proposes an effective way to expose OSC conjugated core to the dopant, which not only improves the charge transfer reaction between organic/dopant semiconductor through cofacial stacking, but also reduces the trap density and contact resistance.