title: Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation.
abstract: We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be -5.93 and -3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10(-6) and 2.1 × 10(-6) cm(2)·V(-1)·s(-1) was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10(-6) cm(2)·V(-1)·s(-1) and a hole mobility of 1.4 × 10(-4) cm(2)·V(-1)·s(-1). The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement.
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Magri
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Pascal
authors.initials: P
authors.lastname: Friederich
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schäfer
authors.affiliation: Istituto per la Sintesi Organica e Fotoreattivitá, Consiglio Nazionale della Ricerca, I-40129 Bologna, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Fattori
authors.affiliation: CIC nanoGUNE Consolider, E-20018 Donostia - San Sebastian, Spain.
authors.forename: Xiangnan
authors.initials: X
authors.lastname: Sun
authors.affiliation: Nanomatch, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Timo
authors.initials: T
authors.lastname: Strunk
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Velimir
authors.initials: V
authors.lastname: Meded
authors.affiliation: CIC nanoGUNE Consolider, E-20018 Donostia - San Sebastian, Spain.
authors.forename: Luis E
authors.initials: LE
authors.lastname: Hueso
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wenzel
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, D-76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Ruben
keywords: HOMO–LUMO energy levels; TFT devices; charge carrier mobility; photophysical characterization; tris-(1-oxo-1H-phenalen-9-olate)aluminum(III)