Investigation of the optoelectronic properties of organic light-emitting transistors based on an intrinsically ambipolar material

Year: 2008

Authors: Capelli R., Dinelli F., Toffanin S., Todescato F., Murgia M., Muccini M., Facchetti A., Marks T.J.

Autors Affiliation: Consiglio Nationale delle Ricerche (CNR), Istituto per lo Studio dei Materiali Nanostrutturati (ISMN), via P. Gobetti 101, 1-40129 Bologna, Italy; Consiglio Nationale delle Ricerche (CNR), Istituto per i Processi Chimico Fisici, via Moruzzi, 1, 1-56124 Pisa, Italy; Department of Chemistry, Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, United States

Abstract: The realization of organic light-emitting transistors (OLETs) based on alpha,omega-dihexylcarbonylquaterthiophene (DHCO4T), an intrinsically ambipolar and luminescent semiconductor, is reported. In this device structure, optimization of the hole/electron density ratio in the channel region has been identified as the major issue to optimize light emission.. Therefore, the focus of this study is to understand how DHCO4T optoelectronic response vary with semiconductor film growth conditions as well as the selection of the gate dielectric and metal contact materials. Our results demonstrate that DHCO4T hole and electron mobilities and the I-DS – V-DS hysteresis mainly depend on the gate dielectric material composition. Atomic force microscopy analysis of the semiconductor film reveals a layer-by-layer growth mechanism, giving rise to the formation of a continuous and homogeneous charge transport layers. With An as the source and drain contact material, the best carrier mobilities have been measured for the poly(methyl methacrylate)-coated SiO2 gate dielectric devices. Metals with Fermi energy ranging from -5.1 to -2.87 eV have also been investigated. Metal deposition on the semiconductor film does not significantly affect film morphology as evidenced by the topography of the electrode top surface. However, for a given dielectric material, the OLET performance strongly depends on the metal/dielectric combination employed and marginally correlates with the contact Fermi energy. Electroluminescence has been observed in DHCO4T-based OLETs but principally in concert with unipolar transport. The hole and electron large gate threshold voltage values have been identified as the principal limitation to high electroluminescence performances.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY C

Volume: 112 (33)      Pages from: 12993  to: 12999

More Information: This work was supported at Bologna by EU under projects FP6-IST-015034 (OLAS) and by Italian Ministry MIUR under Projects FIRB RBNE033KMA, FIRB RBIPO642YL (LUCI), and FIRB – RBIP06JWBH (NODIS), and by Regione Emilia-Romagna under project MISTER. At Northwestern University the work was supported by NSF Europe Program (DMR-0353831) and the NSF MRSEC program (DMR-0520513). The authors thank R. Zamboni for stimulating discussions.
KeyWords: THIN-FILM TRANSISTORS; FIELD-EFFECT TRANSISTORS; SINGLE-CRYSTAL; N-TYPE; SEMICONDUCTORS; TRANSPORT; TEMPERATURE; ELECTRON; PHTHALOCYANINE; STABILITY
DOI: 10.1021/jp7118235

Citations: 38
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