title: Influence of Dielectric Layers on Charge Transport through Diketopyrrolopyrrole-Containing Polymer Films: Dielectric Polarizability vs Capacitance.
abstract: Field-effect mobility of a polymer semiconductor film is known to be enhanced when the gate dielectric interfacing with the film is weakly polarizable. Accordingly, gate dielectrics with lower dielectric constant (k) are preferred for attaining polymer field-effect transistors (PFETs) with larger mobilities. At the same time, it is also known that inducing more charge carriers into the polymer semiconductor films helps in enhancing their field-effect mobility, because the large number of traps presented in such a disorder system can be compensated substantially. In this sense, it may seem that employing higher k dielectrics is rather beneficial because capacitance is proportional to the dielectric constant. This, however, contradicts with the statement above. In this study, we compare the impact of the two, i.e., the polarizability and the capacitance of the gate dielectric, on the transport properties of poly[(diketopyrrolopyrrole)-alt-(2,2'-(1,4-phenylene)bisthiophene)] (PDPPTPT) semiconductor layers in an FET architecture. For the study, three different dielectric layers were employed: fluorinated organic CYTOP (k = ∼2), poly(methyl methacrylate) (k = ∼4), and relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (k = ∼60). The beneficial influence of attaining more carriers in the PDPPTPT films on their charge transport properties was consistently observed from all three systems. However, the more dominant factor determining the large carrier mobility was the low polarizability of the gate dielectric rather than its large capacitance; field-effect mobilities of PDPPTPT films were always larger when lower k dielectric was employed than when higher k dielectric was used. The higher mobilities obtained when using lower k dielectrics could be attributed to the suppressed distribution of the density of localized states (DOS) near the transport level and to the resulting enhanced electronic coupling between the macromolecules.
authors.affiliation: Department of Graphic Arts Information Engineering, Pukyong National University , Sinseon-ro 365, Nam-gu, Busan 608-739, Republic of Korea.
authors.forename: Jiyoul
authors.initials: J
authors.lastname: Lee
authors.affiliation: Organic Materials Lab, Samsung Advanced Institute of Technology, Samsung Electronics Company, Samsung-ro, Suwon, Gyeonggi 443-370, Republic of Korea.|Department of Chemical Engineering, Stanford University , Stanford, California 94305-5025, United States.
authors.forename: Jong Won
authors.initials: JW
authors.lastname: Chung
authors.affiliation: Department of Graphic Arts Information Engineering, Pukyong National University , Sinseon-ro 365, Nam-gu, Busan 608-739, Republic of Korea.
authors.forename: Gyu Bok
authors.initials: GB
authors.lastname: Yoon
authors.forename: Moo Hyung
authors.initials: MH
authors.lastname: Lee
authors.forename: Do Hwan
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , Daehak-ro 291, Yuseong-gu, Daejeon 305-338, Republic of Korea.
authors.forename: Jozeph
authors.initials: J
authors.lastname: Park
authors.affiliation: Department of Polymer Science Engineering, Inha University , Inha-ro 100, Nam-gu, Incheon 402-751, Republic of Korea.
authors.forename: Jin-Kyun
authors.initials: JK
authors.lastname: Lee
authors.forename: Moon Sung
authors.initials: MS
authors.lastname: Kang
keywords: Gaussian disorder model; charge transport; dielectric layer; diketopyrrolopyrrole-containing polymer; polymer field-effect transistors