Evidence and Effects of Ion Transfer at Active‐Material/Electrode Interfaces in Solution‐Fabricated Light‐Emitting Electrochemical Cells

Abstract

The light‐emitting electrochemical cell (LEC) allows for energy‐ and cost‐efficient printing and coating fabrication of its entire device structure, including both electrodes and the single‐layer active material. This attractive fabrication opportunity is enabled by the electrochemical action of mobile ions in the active material. However, a related and up to now overlooked issue is that such solution‐fabricated LECs commonly comprise electrode/active‐material interfaces that are open for transfer of the mobile ions, and it is herein demonstrated that a majority of the mobile anions in a common spray‐coated active material can transfer into a spray‐coated poly(3,4‐ethylenedioxythiophene):poly(styrene‐sulfonate) (PEDOT:PSS) positive electrode during LEC operation. Since it is well established that the mobile ion concentration in the active material has a profound influence on the LEC performance, this significant ion transfer is an important factor that should be considered in the design of low‐cost LEC devices that deliver high performance.

Versatile Biogenic Electrolytes for Highly Performing and Self‐Stable Light‐Emitting Electrochemical Cells

“…[ 19–21 ] As ions source tetrahexylammonium tetrafluoroborate (THABF 4 ) was selected, due to its wide electrochemical stability window. [ 22 ] We rationalize the optimization of the active layers (CA:THABF 4 :CP or Ir‐iTMC) with respect to their morphological, photoluminescence, self‐stability, and ion conductivity features. This resulted in devices with superior performances (stability/efficacy/brightness) compared to their respective references (embedding 0 wt%.…”

A metal-free and transparent light-emitting device by sequential spray-coating fabrication of all layers including PEDOT:PSS for both electrodes

“…Third, the drive voltage of 40 V required to generate significant light emission (in forward bias) is much higher than that of LECs based on the same active material but equipped with a “hard” metal instead of “soft” PEDOT:PSS for the negative cathode. 38,39…”

Water Washable and Flexible Light-Emitting Fibers Based on Electrochemiluminescent Gels

“…Electrochemical stability is another factor to determine the ECL performance of the devices. Low corrosion resistance of Ag paste might result in the formation of Ag + ions instead of oxidized/reduced species of Ru­(bpy) 3 2+ at the Ag/ECL gel interface especially when the bias is sufficiently positive, leading to the degradation of the devices. , In the case of PEDOT:PSS, under the application of a bias, ions from the ECL gel can be injected to the PEDOT:PSS and generate undoped PEDOT:PSS with high resistance, leading to inefficient electrochemical reactions at the ECL gel/PEDOT:PSS interface. , All the devices recorded the maximum luminance at the operating voltage of ±2.4–2.6 V. When larger bias is applied, the luminance property drastically decreases, also probably dueto the degradation of ionic liquid ([EMIM]­[TFSI] in here) in the ECL gel. , Considering the ionic conductivity of ECL gel, we can estimate that the emission delay time of ECL fibers is in the range of a few ms. , …”

“…35,36 In the case of PEDOT:PSS, under the application of a bias, ions from the ECL gel can be injected to the PEDOT:PSS and generate undoped PEDOT:PSS with high resistance, leading to inefficient electrochemical reactions at the ECL gel/PEDOT:PSS interface. 33,37 All the devices recorded the maximum luminance at the operating voltage of ±2.4−2.6 V. When larger bias is applied, the luminance property drastically decreases, also probably dueto the degradation of ionic liquid ([EMIM][TFSI] in here) in the ECL gel. 38,39 Considering the ionic conductivity of ECL gel, we can estimate that the emission delay time of ECL fibers is in the range of a few ms. 28,40 Figure 3d−f shows that all devices exhibited almost identical ECL spectra with a maximum intensity at λ = 620 nm and chromaticity coordinates at (0.67, 0.33), corresponding to the characteristic ECL emission of the Ru(bpy) 3 Cl 2 luminophore.…”