Electric Bias Induced Degradation in Organic-Inorganic Hybrid Perovskite Light-Emitting Diodes

Abstract

For organic-inorganic perovskite to be considered as the most promising materials for light emitting diodes and solar cell applications, the active materials must be proven to be stable under various conditions, such as ambient environment, heat and electrical bias. Understanding the degradation process in organic-inorganic perovskite light emitting diodes (PeLEDs) is important to improve the stability and the performance of the device. We revealed that electrical bias can greatly influence the luminance and external quantum efficiency of PeLEDs. It was found that device performance could be improved under low voltage bias with short operation time, and decreased with continuous operation. The degradation of perovskite film under high electrical bias leads to the decrease of device performance. Variations in the absorption, morphology and element distribution of perovskite films under different electrical bias revealed that organic-inorganic perovskites are unstable at high electrical bias. We bring new insights in the PeLEDs which are crucial for improving the stability.

Operational stability of perovskite light emitting diodes

“…As the first order root cause of device degradation, ion migration inside perovskites can lead to defect migration [41][42][43][44], annihilation and creation of halide Frenkel defects [45][46][47][48][49], modification on charge injection [50][51][52][53][54] and distortion of crystal lattice [35,43,49,55] (figure 1(a)), while ion migration across the interface can lead to corrosion of electrodes [36,[56][57][58][59][60][61] (figure 1(b)). Electrochemical reactions driven by charge injection lead to a decomposition of perovskites into PbI 2 at the anode interface [35,49,62] and a formation of deep traps (Pb 0 interstitials) at the cathode interface [63] (figure 1(c)). Spontaneous chemical reactions between perovskites and other materials in contact with perovskites including metals [36,37], indium-tin oxide (ITO) [38], charge transport materials such as poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) [39] and zinc oxide (ZnO) [40] also lead to device degradation ( figure 1(d)).…”

“…Ion migration inside perovskites can lead to: (i) defect migration [41][42][43][44], (ii) annihilation and creation of Frenkel defects [45][46][47][48][49], (iii) modification on charge injection [50][51][52][53][54] and (iv) distortion of crystal lattice [35,43,49] ( figure 1(a)). In the following discussion, we will show that the first three consequences can give rise to partial reversible changes in device efficiency, while the last one can occur under high driving voltage or prolonged operation, resulting in a completely irreversible degradation.…”

“…However, further study is required to better understand this phenomenon. In addition to the migration of defects, reversible degradation can also be originated from annihilation and creation of halide Frenkel defects [45][46][47][48][49]. Several groups have reported photo-induced PL enhancement in perovskites, and they attributed this phenomenon to annihilation of halide Frenkel defects driven by ion migration (figure 3(a)) [45,47].…”

“…Perovskites can undergo electrochemical reactions under external bias [35,49,62,63], which is another degradation mechanism in perovskite LEDs (figure 1(c)). Electrochemical reactions in perovskites can happen at both the anode and cathode interfaces.…”

“…At the anode interface, these reactions lead to interfacial degradation and it propagates towards the bulk of perovskite through ion migration [35]. Several studies have shown the formation of PbI 2 at the anode side in a lateral device structure [35,49,62] (figure 5). The electrochemical reaction was proposed as follows [35]:…”