Reliability of organic light-emitting diodes in low-temperature environment*

Abstract

Organic light-emitting diode (OLED) is an electroluminescent technology that relies on charge-carrier dynamics and is a potential light source for variable environmental conditions. Here, by exploiting a self-developed low-temperature testing system, we investigated the characteristics of hole/electron transport, electro-optic conversion efficiency, and operation lifetime of OLEDs at low-temperature ranging from –40 °C to 0 °C and room temperature (25 °C). Compared to devices operating at room temperature, the carrier transport capability is significantly decreased with reducing temperature, and especially the mobility of the hole-transporting material (HTM) and electron-transporting material (ETM) at –40 °C decreases from 1.16 × 10−6 cm2/V⋅s and 2.60 × 10−4 cm2/V⋅s to 6.91 × 10−9 cm2/V⋅s and 1.44 × 10−5 cm2/V⋅s, respectively. Indeed, the temperature affects differently on the mobilities of HTM and ETM, which favors unbalanced charge-carrier transport and recombination in OLEDs, thereby leading to the maximum current efficiency decreased from 6.46 cd⋅A−1 at 25 °C to 2.74 cd⋅A−1 at –40 °C. In addition, blue fluorescent OLED at –20 °C has an above 56% lifetime improvement (time to 80% of the initial luminance) over the reference device at room temperature, which is attributed to efficiently dissipating heat generated inside the device by the low-temperature environment.

Toward Improved Device Efficiency and Stability of Organic Light‐Emitting Diodes via External Pressure Treatment

“…[9][10][11][12][13] Although many efforts have been devoted to device stability improvement, less researches were made on the reliability of OLEDs under harsh environmental conditions. [14,15] In particular, in terms of OLED application, one of the significant issues unsolved is the external pressure that the device may encounter. For example, the OLED products may be directly affected by the external pressure, i.e., scene from the sudden dropping to external ornament pasting, to fascinating ocean and space exploration.…”