Charge carrier mobility and electronic properties of Al(Op)₃: impact of excimer formation

Abstract

SummaryWe 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 cm2·V−1·s−1 was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10−6 cm2·V−1·s−1 and a hole mobility of 1.4 × 10−4 cm2·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.

Anodic Deposition of Enantiopure Hexahelicene Layers

“…Based on an evaluation of the potentials for both anodic and cathodic current onsets, one can estimate which of the helicenes undergoes electrochemical transformation more easily. For this purpose, the methodology with ferrocene as an internal standard was used . The anodic current onsets for [5], [6] and [7]helicenes were at +1410 mV, +1405 mV and +1367 mV, respectively.…”

“…For this purpose, the methodology with ferrocene as an internal standard was used. [33] The anodic current onsets for [5], [6] and [7]helicenes were at + 1410 mV, + 1405 mV and + 1367 mV, respectively. The respective current onsets of the major cathodic reactions were found at À2045, À1893 and -1897 mV.…”

Lateral Intermolecular Electronic Interactions of Diketopyrrolopyrrole D−π–A Solar Dye Sensitizers Adsorbed on Mesoporous Alumina

“…Together with the intramolecular CT strength, the type of exciton formed in the dye can be one of the crucial factors that affect the solar cell efficiency. Especially, the CT excitons that form on the donor-containing DPP_A sensitizers can improve the efficiency of the solar cell through the free carrier products generated after the CT excitons, as CT excitons are considered an intermediate stage of charge separation into free carriers. , By contrast, the excimer-like excited state of DPP_R acts as a trap site for excitons or charge carriers − and may delay charge transport, thereby deteriorating the solar cell efficiency. This understanding is beneficial for elucidating the advantages of the D−π–A motif as an efficient dye sensitizer structure, not only for DPP-based dyes but also for other metal-free organic dyes.…”

Bottom-up honeycomb top layer for light outcoupling enhancement in blue organic light emitting diodes

“…To elaborate the electrical model, we took the HOMO/LUMO data from the literature [67,68], as well as the work function of the LiF/Al cathode [66] and the ITO/MoO 3 anode [65]. Electron mobility of BsB 4 is 1.2e 8 cm 2 /Vs [67].…”

“…As we could not find data for hole mobility in BsB4, we tested that our results are practically unchanged upon taking a hole mobility between 1e 5 cm 2 /Vs and 1e 8 cm 2 /Vs for BsB 4 (larger than electron's mobility). In the electron transport layer (ETL), made of Alq 3 , mobilities were assumed to be 1e 5 cm 2 /Vs for electrons and 1e 8 cm 2 /Vs for holes [68]. The Hole transport layer (HTL) is a blend of MoO 3 and BsB 4 that has been modeled as a doped BsB 4 layer.…”