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Effect of solvents on the self-assembly of long chain alkylphosphonic acids on indium tin oxide surface - In situ studies on the adsorption kinetics and electron transfer process
摘要： The spontaneous self-assembly process of phosphonic acids (PAs) onto indium tin oxide (ITO) surface has been studied in this work. We have carried out in situ adsorption kinetics studies of phosphonic acids in ethanol as a solvent using electrochemical impedance spectroscopy (EIS). Further, the effect of different solvents like ethanol, water, toluene and hexane on the structural integrity of the alkylphosphonic acid (CH3 (CH2)n PO3H2, n = 15,17) thin films on ITO surface has been investigated by using [Fe(CN)6]3-/4- as a redox probe. From the study of formation kinetics, it is concluded that molecular self-assembly process follows two adsorption steps, a fast first step followed by a slower second step. The results of cyclic voltammetric (CV) and impedance measurements show that phosphonic acids form a highly impermeable surface film on ITO when polar solvents like ethanol and water are used.
关键词： self assembly,Adsorption Kinetics,microelectrode array,Contact Angle,Capacitance,ITO,Phosphonic acid
更新于2025-09-23 15:23:52
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Schiff Base Ancillary Ligands in Bis(diimine) Copper(I) Dye-Sensitized Solar Cells
摘要： Five 6,6’‐dimethyl‐2,2’‐bipyridine ligands bearing N‐arylmethaniminyl substituents in the 4‐ and 4’‐positions were prepared by Schiff base condensation in which the aryl group is Ph (1), 4‐tolyl (2), 4‐tBuC6H4 (3), 4‐MeOC6H4 (4), and 4‐Me2NC6H4 (5). The homoleptic copper(I) complexes [CuL2][PF6] (L = 1–5) were synthesized and characterized, and the single crystal structure of [Cu(1)2][PF6].Et2O was determined. By using the “surfaces‐as‐ligands, surfaces‐as‐complexes” (SALSAC) approach, the heteroleptic complexes [Cu(6)(Lancillary)]+ in which 6 is the anchoring ligand ((6,6’‐dimethyl‐[2,2’‐bipyridine]‐4,4’‐diyl)bis(4,1‐phenylene))bis(phosphonic acid)) and Lancillary = 1–5 were assembled on FTO‐TiO2 electrodes and incorporated as dyes into n‐type dye‐sensitized solar cells (DSCs). Data from triplicate, fully‐masked DSCs for each dye revealed that the best‐performing sensitizer is [Cu(6)(1)]+, which exhibits photoconversion efficiencies (η) of up to 1.51% compared to 5.74% for the standard reference dye N719. The introduction of the electron‐donating MeO and Me2N groups (Lancillary = 4 and 5) is detrimental, leading to a decrease in the short‐circuit current densities and external quantum efficiencies of the solar cells. In addition, a significant loss in open‐circuit voltage is observed for DSCs sensitized with [Cu(6)(5)]+, which contributes to low values of η for this dye. Comparisons between performances of DSCs containing [Cu(6)(1)]+ and [Cu(6)(4)]+ with those sensitized by analogous dyes lacking the imine bond indicate that the latter prevents efficient electron transfer across the dye.
关键词： Schiff base,phosphonic acid,crystal structure,dye‐sensitized solar cell,copper
更新于2025-09-19 17:13:59
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Self-Assembled Monolayers with Embedded Dipole Moments for Work Function Engineering of Oxide Substrates
摘要： Self-assembled monolayers (SAMs) are frequently used for work function (WF) engineering of different materials. For this, typically dipolar groups are attached to the molecule terminus at the SAM?ambient interface, which also influences its chemistry. WF engineering and interface chemistry can, however, be decoupled from one another using embedded dipolar groups, as has been demonstrated before for thiolate SAMs on metals. Herein, we extend this concept to oxide substrates. For this, a series of biphenyl-based molecules with a phosphonic acid (PA) anchoring group was synthesized, with one of the nonpolar phenyl units exchanged for a polar pyrimidine moiety, the dipole moment of which is oriented either toward (“down”) or away (“up”) to/from the PA group and, consequently, to/from the substrate. SAMs of these molecules formed on indium tin oxide (ITO), a frequently used and application-relevant oxide substrate, feature a uniform molecular configuration, dense molecular packing, and an upright molecular orientation. These SAMs exhibit pronounced electrostatic effects associated with the embedded dipolar groups, viz. shifts of the characteristic peaks in the C 1s X-ray photoelectron spectra and WF variations. The latter values were found to be 3.9, 4.85, and 4.4 eV for the up, down, and nonpolar reference SAM-engineered ITO, respectively. Consequently, these SAMs can serve as a powerful tool to monitor WF engineering effects in a variety of device assembles, decoupling these effects from the interface chemistry. The comparably low WF value for the up SAM is particularly important since it extends a rather limited variety of SAMs capable of lowering the WF of ITO.
关键词： Phosphonic acid,Self-assembled monolayers,Work function engineering,Embedded dipolar groups,Indium tin oxide,Oxide substrates
更新于2025-09-19 17:13:59