SAM engineered heterogeneous interfaces for flexible OFET performance improvement

Solution-processed thiol-based self-assembled monolayers (SAMs) are widely used to align electrode-semiconductor energy levels in flexible organic field-effect transistors (FOFETs), yet how SAM molecules simultaneously influence both electrode and dielectric interfaces in bottom-gate bottom-contact (BGBC) FOFETs remain underexplored. We employed two fluorinated thiols, aromatic and alkyl, to probe how their molecular backbones influence the electrode work function and semiconductor crystallization. Combining experimental characterization with density functional theory (DFT) calculations, the study revealed that aromatic 4-trifluoromethyl-2,3,5,6-tetrafluorothiophenol (TTFP) not only increased the work function (WF) from 3.72 eV to 3.96 eV, but also, through its vertically-standing aromatic rings on the dielectric, facilitated π-π interactions that guide TIPS-pentacene into edge-on orientation, yielding large, highly ordered crystals. This enabled efficient 3 V FOFET operation, with a mobility ( μ ) of 0.32 cm 2 V −1 s −1 (60 % over unmodified), an on/off current ratio ( I on / I off ) of ∼ 10 5 , and a reduced threshold voltage ( V th ) of 0.82 V. Conversely, although the alkyl 1H,1H,2H,2H-perfluorodecanethiol (PFDT) also raised the electrode WF to 3.90 eV, its horizontally-lying chains on the dielectric disrupted π-π stacking, resulting in small, randomly oriented grains and degraded performance. This study reveals the distinct interfacial impacts of aromatic and alkyl thiols in BGBC-FOFETs, guiding rational material selection and FOFETs performance optimization.