Thermal Properties of Polymer Hole-Transport Layers Influence the Efficiency Roll-off and Stability of Perovskite Light-Emitting Diodes

Abstract

While the performance of metal halide perovskite light-emitting diodes (PeLEDs) has rapidly improved in recent years, their stability remains a bottleneck to commercial realization. Here, we show that the thermal stability of polymer hole-transport layers (HTLs) used in PeLEDs represents an important factor influencing the external quantum efficiency (EQE) roll-off and device lifetime. We demonstrate a reduced EQE roll-off, a higher breakdown current density of approximately 6 A cm–2, a maximum radiance of 760 W sr–1 m–2, and a longer device lifetime for PeLEDs using polymer HTLs with high glass-transition temperatures. Furthermore, for devices driven by nanosecond electrical pulses, a record high radiance of 1.23 MW sr–1 m–2 and an EQE of approximately 1.92% at 14.6 kA cm–2 are achieved. Thermally stable polymer HTLs enable stable operation of PeLEDs that can sustain more than 11.7 million electrical pulses at 1 kA cm–2 before device failure.

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“…However, it is worth noting the efficiency roll-off is obvious, which might be ascribed to Joule heating. 53–55 And generally, an obvious Joule heating effect was caused by the non-radiative recombination and the large current density generally. Therefore, further improving the PLQY and weakening the intermolecular interactions may help to reduce the Joule heating effect.…”

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“…Nevertheless, the ability to maintain operation at high current density is a prerequisite for PeLEDs to achieve high brightness. Figure shows the timelines for the maximum current densities of PeLEDs achieved over the years. − Notably, driven by nanosecond electrical pulses, the maximum current density of PeLEDs has exceeded 20 kA cm –2 , and the maximum current density, driven continuously, has achieved 25 A cm –2 . These reports show the promise for high-power PeLED operations.…”

High-Performance All-Inorganic Architecture Perovskite Light-Emitting Diodes Based on Tens-of-Nanometers-Sized CsPbBr3 Emitters in a Carrier-Confined Heterostructure

“…However, for most high-efficiency green PeLEDs, the peak EQEs are achieved at low brightness and start to droop at high brightness, known as efficiency roll-off. This phenomenon can be attributed to nonradiative Auger recombination , and/or joule heating, − and degradation at the interface between perovskites and organic materials. − …”

“…Additionally, the bulky organic ligands in these nanostructured emitters may obstruct charge transport, causing a charge imbalance within the device. Furthermore, the organic charge-transporting layers (CTLs) may be unstable under high current density, and the ions present in perovskites can potentially penetrate the organic CTLs under the electric field, degrading the interface. Consequently, green PeLEDs often suffer from efficiency roll-off at a high brightness.…”