As a new device platform
comprising only electrochemiluminescence
(ECL) luminophores and an electrolyte sandwiched between electrodes,
ECL devices (ECLDs) promise to be cost efficient for large-area emissive
applications. However, rapid degradation of luminescence, along with
thermal decomposition of the electrochemical components, has proven
a seemingly fundamental problem in ECLDs. To alleviate this issue,
we investigated the influence of inserting a resting period during
the operation of such devices by applying a square-shaped pulsed signal.
The inserted resting period enhances the device stability, as it allows
the effective reaction volume near the electrodes to be replenished
with ECL luminophores, thus, preventing undesired side reactions.
Moreover, the application of a current pulsed signal, rather than
a voltage pulse, leads to further enhancement of the device stability,
attributable to even distribution of the redox reaction over the rough
surface of the electrode under current control. Under controlled pulsed-current
operation (100 μA at 10 Hz), the emission characteristics of
an ECLD employing a neutral iridium(III) complex as the luminophore
can be preserved for ∼1 h.
Iridium(III) bis(2-phenylpyridinato-N,C 2 ')acetylacetonate ((ppy) 2 Ir(acac)), a green dopant used in organic light-emitting devices (OLEDs), was subjected to electrochemical characterization to estimate its formal oxidation potential (E o '), HOMO energy level (E H O M O), electron transfer rate constant (k o '), and diffusion coefficient (D o). The employed combination of voltammetric methods, i.e., cyclic voltammetry (CV), chronocoulometry (CC), and the Nicholson method, provided meaningful insights into the electron transfer kinetics of (ppy) 2 Ir(acac), allowing the determination of k o ' and D o. The quasireversible oxidation of (ppy) 2 Ir(acac) furnished information on E o ' and E H O M O , allowing the latter parameter to be easily estimated by electrochemical methods without relying on expensive and complex ultraviolet photoemission spectroscopic (UPS) measurements.
Two voltammetric techniques, cyclic voltammetry (CV) and chronocoulometry (CC), were used to investigate the redox characteristics of an organic semiconductor, 2,2 0 ,7,7 0 -tetrakis(diphenylamino)-9,9 0spirobifluorene (spiro-TAD). The electron-transfer characteristics of spiro-TAD, including the formal oxidation potentials (E o0 ), diffusion coefficients (D o ), and electron-transfer rate constants (k o0 ), were estimated by a combination of CV and CC measurements. The energy of the highest-occupied molecular-orbital could also be found from the quantitative relationship between the oxidation potential and the ionization energy.
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