Organic field-effect transistors with molecularly doped polymer gate buffer layer

Organic field-effect transistors (OFETs) with molecularly doped poly(methylmethacrylate) (PMMA) gate buffer layer were newly investigated. Acceptor doped PMMA buffer layers with a thickness of 8 nm were deposited onto SiO2 gate insulator by spin-coating methylethylketone solution containing both PMMA and molecular dopants such as tetrafluorotetracyanoquinodimethane (F4TCNQ). Gate threshold voltage shifts in positive direction were commonly observed for both p-channel and n-channel transistors with F4TCNQ doped PMMA gate buffer layer. In p-channel pentacene thin-film transistors, higher dopant ratio led to the increase in the effective hole mobility due to hole doping caused by charge transfer between pentacene and F4TCNQ molecules. In n-channel transistors based on 1,4,5,8-naphthalenetetracarboxylicdianhydride (NTCDA) and copper hexadecafluorophthalocyanine (F16CuPc), F4TCNQ molecules doped into the PMMA layer behave as electron traps and NTCDA transistors are more susceptible to acceptor dopants than F16CuPc ones. This phenomenon in the n-channel transistors can be explained by energetic differences between unoccupied molecular orbital (LUMO) levels of host organic semiconductor and dopant molecules.