The Effect Of Gate Dielectrics And Polar Impurities On Electron Transport In TIPS-pentacene Single Crystals

Organic field-effect transistors(OFETs)have attracted tremendous interest for their low-cost,lightweight and large-area applications.Organic single crystals,as compared with the amorphous or polycrystalline thin films,are better for investigating charge transport in organic materials due to their higher order and fewer structure defects.In recent years,researchers have found that choosing the suitable gate dielectric is extremely important to the performance of OFETs.The researches are mainly focused on the effects of gate dielectric on the performance of p-type OFETs,instead of n-type.Very recently,we discovered an unusual electron transport in TIPS-pentacene(6,13-bis(triisopropyl-silylethynyl)pentacene).Although TIPS-pentacene is recognized as a typical p-channel semiconductor as Au is used for the source-drain electrodes,electron transport emerges as TIPS-pentacene crystallizes on divinyl-tetramethyldisiloxane-bis(benzocyclobutene)(BCB)dielectric from non-polar solvents.In contrast,the electron transportation is suppressed by the polar solvent residues as TIPS-pentacene crystallizes from polar solvents.From this point,we aim to reconfirm and further examine the effects of gate dielectrics and polar impurities on the electron transport in TIPS-pentacene single crystals.In Chapter 1,preparation approaches of organic semiconducting single crystals,fabrication and applications of OFETs,and the effects of polymer dielectrics on the performance of electronic devices are reviewed.In Chapter 2,we studied the effects of gate dielectrics and polar impurities on the electron transport in TIPS-pentacene single crystals.Electron transport was obtained on polystyrene(PS),poly(methyl methacrylate)(PMMA),and poly(vinyl alcohol)(PVA)as well as a bilayer dielectric of PMMA on poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)(P(VDF-TrFE-CFE)).The highest electron mobility of 0.48 cm2V-1s-1 has been achieved in the crystals on PMMA.We also found a decrease of electron mobility with the increase of the dielectric constants.Subsequently,we discovered that the electron transport was sensitive to the polar impurities.Exposure to the vapor of a variety of polar solvents including chloroform(CHCl3),dichloromethane(CH2Cl2),1,2-dichloroethane(ClCH2CH2Cl)and tetrahydrofuran(THF)results in dramatically reduced electron mobility.In Chapter 3,we discussed the effect of hydroxyl groups on the electron transport in TIPS-pentacene single crystals.We found that aliphatic alcohol was not easy to trap electron due to its high dissociation constant(pKa?15),and electron transport could be obtained on dielectrics that contain aliphatic alcohol.In sharp contrast,aromatic alcohol is easier to dissociate protons and trap electrons,which suppress the electron transport in TIPS-pentacene single crystals.