For bright area light sources, such as OLED lighting tiles, the electric resistivity of transparent electrodes induces a non-uniform current distribution within the device. At high driving currents, the interaction between conductivity, heat, and power dissipation results in a positive electrothermal feedback loop, which drastically exacerbates inhomogenities in local device temperature and luminance.
Such nonlinear behavior induces unprecedented electrothermal effects that compromise the performance of bright area light sources. In this contribution, we discuss how Joule self-heating sqeezes temperature and current into a tiny device region, while the remainder of the active area decreases in luminance (Switch-back effect). We further introduce how the dimension of the active area governs the current-voltage characteristics of the OLED and how two and even three stable operating branches develop (tristability) that can promote destructive incidences.
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