Electron Density‐Change in Semiconductor by Ion‐Adsorption at Solid–Liquid Interface

Abstract

The change in electrical properties of electrodes by adsorption or desorption at interfaces is a well‐known phenomenon required for signal production in electrically transduced sensing technologies. Furthermore, in terms of electrolyte–insulator–semiconductor (EIS) structure, several studies of energy conversion techniques focused on ion‐adsorption at the solid–liquid interface have suggested that the electric signal is generated by ionovoltaic phenomena. However, finding substantial clues for the ion‐adsorption phenomena in the EIS structure is still a difficult task because direct evidence for carrier accumulation in semiconductors by Coulomb interactions is insufficient. Here, a sophisticated Hall measurement system is demonstrated to quantitatively analyze accumulated electron density‐change inside the semiconductor depending on the ion‐adsorption at the solid–liquid interface. Also, an enhanced EIS‐structured device is designed in an aqueous‐soaked system that works with the ionovoltaic principle to monitor the ion‐dynamics in liquid electrolyte media, interestingly confirming ion‐concentration dependence and ion‐specificity by generated peak voltages. This newly introduced peculiar method contributes to an in‐depth understanding of the ionovoltaic phenomena in terms of carrier actions in the semiconductors and ionic behaviors in the aqueous‐bulk phases, providing informative analysis about interfacial adsorptions that can expand the scope of ion‐sensing platforms.

Verification of Carrier Concentration‐Dependent Behavior in Water‐Infiltration‐Induced Electricity Generation by Ionovoltaic Effect

“…Based on the above results, we confirmed that the carrier concentration of PCNF played a crucial role in the electricity generation during water infiltration, and its effect was verified by the ionovoltaic effect [8,[11][12][13][14][15] accurately. The ionovoltaic effect refers to the electricity generation by the change in surface properties via ion dynamic motions, such as ion adsorption.…”

“…Herein, we verified the effect of semiconductor carrier concentration, a crucial factor on electricity generation during water infiltration. By comprehensively investigating this factor on electricity generation, we accurately demonstrated the energy harvesting mechanism of the ionovoltaic effect [8,[11][12][13][14][15] via energy band theory in semiconductors. Briefly, the behavior of ions adsorption on the nanostructured semiconductor surface altered its carrier concentration, which induced a potential difference between wet and dry regions and generated electrical energy.…”

Ionic Diffusion‐Driven Ionovoltaic Transducer for Probing Ion‐Molecular Interactions at Solid–Liquid Interface

“…line with various water-motion-induced electricity-generating phenomena, ion dynamics in the electrolyte can induce spatially asymmetric potential in the semiconductor, an electromotive force for electricity generation. [20] However, understanding and controlling the ionovoltaic effect in semiconducting materials remains imperative since multipronged influences of these dipole potential effects from the electrolyte part to the electrode layer were raised as indispensably investigating areas. [16,17,22] In this study, the interfacial potential effect of the surficial molecular layer in the ESS structure was investigated through an ionic diffusion-induced ionovoltaic transducer (IIT).…”

“…Lately, this was experimentally proved through a liquid‐adjoining Hall measurement in ESS structure, which verified that the ion adsorption on SAM could offer a self‐gating (without an external gate potential) effect, thereby accumulating charge carriers at the SAM–semiconductor interface. [ 2 , 20 ] These results suggested that, as the semiconductor has a less charge screening capability than a metallic electrode, it can sensitively vary its charge carrier density near the SAM–semiconductor interface depending on the electrolyte condition. [ 2 , 21 ] Hence, in the same line with various water‐motion‐induced electricity‐generating phenomena, ion dynamics in the electrolyte can induce spatially asymmetric potential in the semiconductor, an electromotive force for electricity generation.…”

Probing an Interfacial Ionic Pairing‐Induced Molecular Dipole Effect in Ionovoltaic System

“…[11,15,16] As a discerning method of solid/liquid interfacial states, an ionovoltaic generation, converting the interfacial potential effects on the electrolyte/dielectric (SAM and insulating layer)/electrode interface to electric signals, has been proposed, and correlative studies were conducted for investigating its mechanism. [17][18][19][20][21] The interfacial potential gradient, emanating from the intrinsic molecular dipole of SAM, was revealed to an origin of electric signals, and through this, such a system was demonstrated to sensitively probe the interfacial potential alteration by chemical interactions within the electrolytes/SAM interface (e.g., de-/protonation and ion complexation). [9,22] Hence, along with varying the SAM design, specific ion-molecular interactions at the liquid/ SAM interface could be interrogated through an intuitive observation of electrical output changes on the ionovoltaic system.…”