Rationalizing energy level alignment by characterizing Lewis acid/base and ionic interactions at printable semiconductor/ionic liquid interfaces

Abstract

Chemical and ionic interactions between an ionic liquid and printable semiconductors are probed by photoelectron spectroscopy, with increasing reactivity associated with underlying defects from P3HT to NiOx to PbS/PbIx quantum dots to MAPbI3.

Flexible pH sensors based on OECTs with a BTB dye-embedded ion-gel gate dielectric

“…4c, d and f, it is observed that both [BMIM] + and [TFSI] − are present in the channel. 31 The injection of [TFSI] − and [BMIM] + can cause the doping and de-doping of the PEDOT:PSS channel, respectively. As the pH value increases from 2 to 9, the number of [BMIM] + in the channel increases but that of the [TFSI] − decreases.…”

Electronic States of Pentacene Thin Films at Interfaces with Ionic-Liquid Layers Probed by Photoelectron Yield Spectroscopy

“…The first peak in the second derivative of the PY spectra was fitted by a single Gaussian function and normalized by the area of the Gaussian fitting curve for each sample. Here, we emphasize that the HOMO peak is visible even at a thickness of 5 nm, whereas the HOMO peak for the underlayer is unclear in the UP spectra. − The characteristic parameters of the peak top energy ( E top ) and the width (standard deviation, σ) obtained from the Gaussian fitting analysis were plotted against the nominal thickness of DEME-TFSI (Figure c). The thickness dependence of the peak top energy will be discussed later together with the IE.…”

“…Various experimental techniques, including frequency modulation atomic force microscopy (FM-AFM), − X-ray and neutron reflectometry, , electron paramagnetic resonance, − charge-accumulation spectroscopy, , attenuated total reflection spectroscopy, , and X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS), − have been developed and employed to elucidate the molecular orientation, molecular arrangements, charge/spin states, and electronic states at organic layer–IL (or electrolyte) interfaces. Among them, XPS and UPS have been employed the most for the measurement of electronic states.…”

“…In particular, UPS has been employed to directly probe the highest occupied molecular orbital (HOMO) and its related states. − Although the interfacial electronic states of the HOMO in organic layers have been obtained at the interface with ILs, the intensity of the HOMO peak in UPS significantly decreases and becomes undetectable when the thickness of the IL layers is over 1 nm. − The acquisition of photoelectron signals emitted from the organic layers is thus impeded by the overlayers because the probing depth of UPS is generally limited to <1 nm, attributed to the short effective attenuation length of photoelectrons with kinetic energies in the range of 10–100 eV . Furthermore, the interfacial energy diagram has been drawn by recording the electronic states of the topmost surface layers step by step by sequential deposition . However, the interfacial energy diagram obtained using this method does not consider the influence of an additional layer on the electronic states of the underlayer, such as the polarization effect, , which hinders the in-depth discussion on and comprehensive understanding of the interfacial electronic states.…”

“…34 Furthermore, the interfacial energy diagram has been drawn by recording the electronic states of the topmost surface layers step by step by sequential deposition. 33 However, the interfacial energy diagram obtained using this method does not consider the influence of an additional layer on the electronic states of the underlayer, such as the polarization effect, 35,36 which hinders the in-depth discussion on and comprehensive understanding of the interfacial electronic states. Therefore, the direct probing of the interfacial electronic states of organic layers covered by IL layers with thicknesses larger than a few nanometers is challenging.…”