High ON/OFF ratio and stability of amorphous organic field-effect transistors based on spiro-linked compounds

We report high ON/OFF ratios for organic field-effect transistors (OFETs) based on amorphous thin films of spiro-linked compounds. Bottom-contact OFET structures are fabricated, using 2,2′,7,7′-tetra-(m-tolyl-phenylamino)-9,9′-spirobifluorene (Spiro-TPD) and 2,2′,7,7′-tetrakis-(diphenylamino)-9,9′-spirobifluorene (Spiro-TAD) as active materials. The field-effect mobility of holes in Spiro-TPD and Spiro-TAD thin films is 7 × 10−5 cm2/Vs. We obtained ON/OFF ratios up to 3.6 × 106 with low OFF currents in the pA range. Time-dependent measurements show that the transistor characteristics do not change significantly over 9 months.