In the past few years, the efficiency of organic metal halide perovskite based light emitting diodes (peleds) has been significantly improved. However, the poor operation stability of the device hinders the commercialization of the technology in practical application. Although the degradation mechanism of perovskite films has been widely studied, it is still unclear where and how perovskite films degrade.

A new study from the Chinese University of Hong Kong and Sun Yat sen University shows that the degradation may start from the interface between perovskite and hole transport layer, and vacancy, inversion or gap defects can further accelerate this degradation. When the current density is 100 Ma · cm-2, the stability of the passivated film is greatly improved, and the operating life is increased from 1.5 h to 11.3 H. Relevant papers were published on advanced functional materials with the title of “degradation mechanism of perovskite light emitting diodes: an in situ investigation via electroabsorption spectroscopy and device modeling”.

Organic metal halide perovskite based light emitting diode materials have the advantages of low manufacturing cost, tunable band gap, high color purity, high luminous efficiency and good compatibility with flexible substrates. They have great application potential in the field of display and lighting. In recent years, many research breakthroughs have been made in the luminescence characteristics of peleds. The external quantum efficiency (EQE) and emissivity of near-infrared peleds with the best performance have reached 21.6% and 308 w (SR) respectively × m2)−1。 However, most reported peleds degrade rapidly during operation and lose luminescence within hours. Stability is a common problem in almost all perovskite optoelectronic devices, especially in peleds with high current density and low energy conversion efficiency.

The degradation process was studied in situ by electroabsorption (EA) spectroscopy. Spectroscopy can monitor the changes of light absorption of materials under electric field modulation, and has been applied to the study of various materials and biological systems. In particular, EA spectroscopy has proved to be a powerful tool to characterize the band gap, exciton binding energy, dipole moment change and charge polarization of perovskite materials. Considering that different complexes have different absorption characteristic peaks, it is possible to distinguish the property changes of each functional layer in the device by EA spectroscopy. For example, previous studies have applied EA to study different functional layers with organic light emitting diodes or solar cells. In this paper, electron spectroscopy is used to evaluate the stability of each functional layer by monitoring its unique optical characteristics. The time-varying EA spectrum analysis clearly shows that the degradation mainly occurs in the calcium titanium deposit.

Analysis of the problem of short luminescence duration of perovskite LED

Fig. 1 a) structural diagram of peleds device. b) (a) energy level diagram of the device shown. c) Electroluminescence spectra under different operating bias. d) The current voltage curve of typical peleds monitored in this paper and E) the relationship between current irradiance and current brightness. f) EQE decay curve with time when the current density is 100 Ma cm − 2.

Analysis of the problem of short luminescence duration of perovskite LED

Fig. 2 in the presence of a) iodine vacancy defect (VI) with an energy level of 0.03 EV below the conduction band, b) lead vacancy defect (VPB) with an energy level of 0.04 EV above the valence band, the simulated recombination rate of our peleds device, with an injection current density of 100 Ma cm − 2, c) gap defect trap (II) with an energy level of 0.6 EV above the valence band, d) anti dislocation defect trap (IPB) with an energy level of 1.0 EV above the valence band, e) Non radiative recombination rate distribution along the vertical direction.

Analysis of the problem of short luminescence duration of perovskite LED

Fig. 3 A) current voltage characteristics, b) comparison of brightness and current density under different peai concentrations. c) El spectrum comparison, d) comparison of operation stability of peleds with and without peai layer. Time dependent EA spectra with E) and without f) peai layer at current density of 100 Ma cm − 2.

Analysis of the problem of short luminescence duration of perovskite LED

Fig. 4 Schematic diagram of perovskite surface lattice structure (left panel) and device model of peleds (right panel) a) and b) without peai passivation treatment. The blue and red arrows indicate the transport direction of electrons and holes, respectively.

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