Self‐Heating in Light‐Emitting Electrochemical Cells

Abstract

Electroluminescent devices become warm during operation, and their performance can, therefore, be severely limited at high drive current density. Herein, the effects of this self‐heating on the operation of a light‐emitting electrochemical cell (LEC) are systematically studied. A drive current density of 50 mA cm−2 can result in a local device temperature for a free‐standing LEC that exceeds 50 °C within a short period of operation, which in turn induces premature device degradation as manifested in the rapidly decreasing luminance and increasing voltage. Furthermore, this undesired self‐heating for a free‐standing thin‐film LEC can be suppressed by the employment of a device architecture featuring high thermal conductance and a small emission‐area fill factor, since the corresponding improved heat conduction to the nonemissive regions facilitates more efficient heat transfer to the ambient surroundings. In addition, the reported differences in performance between small‐area and large‐area LECs as well as between flexible‐plastic and rigid‐glass LECs are rationalized, culminating in insights that can be useful for the rational design of LEC devices with suppressed self‐heating and high performance.

Controlling the Emission Zone by Additives for Improved Light‐Emitting Electrochemical Cells

“…An Al heat sink was placed behind the LEC device to mitigate undesired self‐heating effects during electrical driving. [ 28 ] The angle‐resolved EL intensity and spectrum of the LEC devices were measured with a custom‐built, automated spectrogoniometer setup, as schematically depicted in Figure 1c. The device under study was placed in a connection jig, which aligned the emission area of the device with the rotation axis of a stepper motor.…”

Facile generation of thenil and furil based blue emitters for the fabrication of non-doped and solution-processed light-emitting electrochemical cells

“…Morphological and thermal stabilities are crucial to fabricate excellent LECs with good operational stability. 41,42 On increasing the operational voltage to obtain high brightness, the non-radiative relaxation process from the device also increases. Good thermal stability is important as it imparts better thin film forming ability and thereby reducing the efficiency roll-off.…”

Revealing the Impact of Heat Generation Using Nanographene-Based Light-Emitting Electrochemical Cells

“…18,[20][21][22][23][24] Much less considered is the impact of the self-heating in LECs caused by the operating conditions. 25 Similar to other thin-film organic/inorganic lighting diodes, 26 the instantaneous heat generation upon driving is related to i) the resistances associated to the interfaces and the bulk of the active layer (Joule effect), and ii) the non-radiative deactivation process of excitons (formation of dark/quenched excitons and self-absorption). In LECs, self-heating might also be a source of emitter degradation, exciton dissociation, quick collapse of the intrinsic emitting zone, and morphological changes, since the internal temperature of the devices can reach values close to 80 ºC.…”

“…For instance, Figure S1 displays the working pixel temperature of 40-50 °C LECs with d 6 -/d 10 -complexes and small molecules operating at pulsed 100 mA/cm 2 , 7,24,40 while Edman's group has recently showed that polymer-LECs reach 50 °C at 50 mA/cm 2 . 25 Our interest on nanographenes lies on their high ϕ, ambipolar carrier properties, sound thermal and redox stabilities, and a good solubility in common organic solvents. 32,41,42 Despite these appealing properties, they have barely been investigated as emitters in thin-film lighting devices.…”