Air-operable, high-mobility organic transistors with semifluorinated side chains and unsubstituted naphthalenetetracarboxylic diimide cores: High mobility and environmental and bias stress stability from the perfluorooctylpropyl side chain

N,N′-bis(3-(perfluoroctyl)propyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (8-3-NTCDI) was newly synthesized, as were related fluorooctylalkyl-NTCDIs and alkyl-NTCDIs. The 8-3-NTCDI-based organic thin-film transistor (OTFT) on an octadecyltrimethoxysilane (OTS)-treated Si/SiO ₂ substrate shows apparent electron mobility approaching 0.7 cm ² V^-1s^-1 in air. The fl uorooctylethyl-NTCDI (8-2-NTCDI) and fluorooctylbutyl-NTCDI (8-4-NTCDI) had significantly inferior properties even though their chemical structures are only slightly different, and nonfluorinated decyl and undecyl NTCDIs did not operate predictably in air. From atomic force microscopy, the 8-3-NTCDI active layer deposited with the substrate at 120 ° C forms a polycrystalline film with grain sizes >4μm. Mobilities were stable in air for one week. After 100 days in air, the average mobility of three OTFTs decreased from 0.62 to 0.12 cm² V^-1s^-1, but stabilized thereafter. The threshold voltage (V_T) increased by 15 V in air, but only by 3 V under nitrogen, after one week. On/off ratios were stable in air throughout. We also investigated transistor stability to gate bias stress. The transistor on hexamethlydisilazane (HMDS) is more stable than that on OTS with mobility comparable to amorphous Si TFTs. V_T shifts caused by ON (30 V) and OFF (-20 V) gate bias stress for the HMDS samples for 1 hour were 1.79 V and 1.27 V under N₂, respectively, and relaxation times of 10⁶ and 10⁷ s were obtained using the stretched exponential model. These performances are promising for use in transparent display backplanes.