Surface-Doping-Induced Mobility Modulation Effect for Transport Enhancement in Organic Single-Crystal Transistors

Molecular doping has conventionally been an effective way to improve the electrical-transport performances in organic field-effect transistors (OFETs), while corresponding mechanisms associated with specific doping techniques have been less investigated and discussed in detail. Here, based on ultrathin dinaphtho[2,3-b:2 ',3 '-f]-thieno[3,2-b]thiophene (DNTT) single crystals, robust transconductance enhancements are realized in OFETs upon surface molecular doping realized via van der Waals epitaxially growing crystalline 1,3,4,5,7,8-hexafluoro-tetracyanonaphthoquinodimethane (F6TCNNQ) onto the single crystal's surface. It is proposed that it is the mobility modulation effect (MME) from the interactions between charge-transfer interface and gate electric field, that contributes to more weighted bulk carriers, and finally improves charge-transport performances. The evaluations are further supported by scanning Kelvin probe microscopy (SKPM) surface potential characterizations, which manifest the gate-induced more delocalized holes near the charge-transfer interfaces. Space-charge-limited current (SCLC) investigations, numerical calculations, and theoretical mobility modeling are also performed to corroborate the analysis. This study can deepen the understanding of charge transport in doped semiconductors and provide effective ways for optimizing the electrical performance of organic devices.