Investigation of charge transport of monolayer polymeric films with field effect tuning and molecular doping for chemiresistive sensing application

Abstract

Semiconducting and conducting 2D conjugated polymers have been widely investigated due to their merits such as mechanical flexibility, solution processability, and large-area fabrication. Nevertheless, the transport characteristics of field-effect tuning and molecule doping ultra-thin even monolayer conjugated polymers haven't been understood thoroughly. Moreover, a general and facile method for the direct synthesis of large-area conjugated polymer monolayer films with good uniformity and high coverage on the SiO2/Si substrates is highly desirable and still remains challenging. Here, we have used the simple drop-casting method to successfully fabricate high-coverage and homogeneous poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno [3], [2-b]thiophene) (PBTTT) monolayer films directly on the surface of SiO2/Si substrate. The electrical transport behaviors were investigated systematically in both field effect doping and molecular doping the systems. 2D hopping transport was observed dominating the conductance of the field effect tuned monolayer PBTTT. While Efros-Shklovskii variable range hopping (ES-VRH) contributed the main transport at higher carrier concentration system doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). And the onset interlayer transport should effectively reduce the energetic disorder revealed in bi- or tri-layer films. In addition, the F4-TCNQ doping conductive PBTTT monolayer films displayed superior chemiresistive sensing toward ammonia. The proposed semiconducting and conducting conjugated polymer monolayer-based ideal platform can open new avenues for ultra-thin film organic electronics.