|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||H3, Arylene Diimide-Thiophene Semiconductors for n-Channel Field-Effect Transistors
||Rocio Ponce Ortiz, Hui Huang, Antonio Facchetti, Tobin J. Marks, Yan Zheng, Raul Blanco, Helena Herrera, Jose L. Segura
|On-Site Speaker (Planned)
||Rocio Ponce Ortiz
Oligothiophenes and arylene-diimide derivatives are among the most used semiconductors in the fabrication of Organic Field Effect Transistors (OFETs). One intriguing strategy to improve the electrical behavior and/or achieve ambipolarity in organic semiconductors would be the combination of arylene diimide skeleton with thiophene rings within the same molecular structure. To this end, we have fabricated the first family of molecules consisting of β-naphthalenediimide and β-perylenediimide oligothiophenes. This family of semiconductors allows us to analyze the interplay of three different effects on device response: (i) oligothiophene backbone catenation; (ii) interchanging naphthalenediimide by perylenediimide substituents, and (iii) introducing a phenylene group in the olighothiophene backbone. Amphoteric redox behavior is recorded in these molecules by cyclic voltammetry, indicating the possibility of both electron extraction and injection from/into the conjugated π-system. Electrical measurements of vapor-deposited films measured in vacuum show electron field-effect mobilities as high as 0.35 cm<SUP>2</SUP>V<SUP>-1</SUP>s<SUP>-1</SUP> for semiconductor NDI-1T. Lower mobilities, on the order of 0.1-10-4 cm<SUP>2</SUP>V<SUP>-1</SUP>s<SUP>-1</SUP>, are recorded for the remainder of the semiconductors. The remarkable variation in electrical behavior within the semiconductor family is analyzed by means of electrochemistry experiments, X-ray diffraction and Atomic Force Microscopy (AFM), and is aided by theoretical Density Functional Theory (DFT) calculations. It will be shown that the differences in carrier mobilities can be basically explained on the basis of molecular packing and film microstructural trends. Indeed, the best device performance is measured for NDI-1T films, where calculations predict the molecule to be basically flat, thus promoting a closely packed crystalline film which is consistent with a well-resolved single phase XRD pattern. Furthermore, AFM reveals the presence of large and well-connected grains. On the contrary, the poor electrical performance of NDI-3T is likely connected with the poor film crystallinity (in fact no diffraction peaks are detected in XRD experiments) and with the presence of very small grains with increased grain boundaries. Solution-processed OFETs were also fabricated and their electrical performance compared with that of the corresponding vapor-deposited films. Field-effect mobilities of 0.042 cm<SUP>2</SUP>V<SUP>-1</SUP>s<SUP>-1</SUP> and 0.011 cm<SUP>2</SUP>V<SUP>-1</SUP>s<SUP>-1</SUP> were obtained for PDI-1T and PDI-3T, respectively.