Operationally Stable Perovskite Light Emitting Diodes with High Radiance

Abstract

Although perovskite light emitting diodes (PeLEDs) have shown fast advances in external quantum efficiency (EQE), their operational stability is still low compared to other LED devices. Here, stable PeLEDs are demonstrated with high radiance primarily by using 6,6′‐phenyl‐C61‐butyric acid methyl ester (PCBM) and magnesium‐doped Zinc oxide (ZnMgO) injection layers to reduce the driving voltage. Through different characterizations, it is revealed that the use of PCBM/ZnMgO electron injection layer can effectively mitigate Joule heating, block the migration of Al electrode towards perovskite layer as well as avoid the breakdown of main perovskite crystal structure under prolonged operation. Combining the PCBM/ZnMgO electron injection layer with a formamidinium‐based perovskite light emitter, the optimal device shows an EQE of 11.4% at 330 mA cm−2 and a radiance of 399 W Sr−1 m−2 at 3.1 V. The device remains above 50% of the maximum performance after operating for 525 and 118 h at constant current densities of 50 and 100 mA cm−2, respectively. Thus, this work presents a substantial improvement in the stability of PeLEDs and the methods to consolidate this progress even further.

Ion Migration in Perovskite Light‐Emitting Diodes: Mechanism, Characterizations, and Material and Device Engineering

“…According to the theoretical calculations described in Section 2.1, vacancies and interstitials of A‐site cation and halide ions (e.g., V I , V MA , I i , and MA i ) are most likely to cause operational instability of PeLEDs due to the relatively low formation energy of these defects and low activation energy for their migration. Experimentally, migration of halide ions in operating PeLEDs has been widely observed, [ 30,35,111,112 ] and there have also been reports on detection of simultaneous migration of both halide ions and A‐site cations (e.g., Cs + , [ 113,114 ] MA + , [ 33 ] and FA +[ 34 ] ), which will be discussed in the following sections.…”

“…[ 111 ] The formation of a mixed interface between Al electrodes in degraded devices has also been verified through TOF‐SIMS depth‐profiling measurements. [ 112,125 ]…”

“…Additionally, metal electrodes [ 99,100,125 ] and Sn [ 189 ] atoms (from ITO) can diffuse into perovskite layers and generate quenching sites. [ 111,112 ] In a MAPbBr 3 LED, decomposition into gaseous methylamine and hydrogen bromide was observed, resulting in cathode delamination and a subsequent reduction in EQE; the device performance was partially recovered through deposition of a new electrode (Figure 7i). [ 103 ] Moreover, the rising junction temperature generated by Joule heating could induce thermal decomposition [ 125,190 ] or accelerate ion‐related effects.…”

“…[111] The formation of a mixed interface between Al electrodes in degraded devices has also been verified through TOF-SIMS depth-profiling measurements. [112,125] Figure 5. a) STEM-EDX maps of bromine (Br-Kα) distribution for a pristine device (top) and a device after 3 h of operation at 2 V (bottom), together with the corresponding averaged bromine intensities.…”

P‐92: Effects of Self‐Absorption and Photon Recycling in Metal‐Halide Perovskite LEDs Assessed by Full Opto‐Electronic Device Simulation

“…Furthermore, we apply a spectral shift to the optical data (wrt energy) in order to reproduce the experimentally observed peak position. For the electrical simulation, the data for band alignment and mobilities are taken again from the literature [3,8].…”