Enabling Self-passivation by Attaching Small Grains on Surfaces of Large Grains toward High-Performance Perovskite LEDs

Abstract

This paper reports a new method to generate stable and high-brightness electroluminescence (EL) by subsequently growing large/small grains at micro/nano scales with the configuration of attaching small grains on the surfaces of large grains in perovskite (MAPbBr 3) films by mixing two precursor solutions (PbBr 2 + MABr and Pb(Ac) 2 $3H 2 O + MABr). Consequently, the small and large grains serve, respectively, as passivation agents and light-emitting centers, enabling self-passivation on the defects located on the surfaces of light-emitting large grains. Furthermore, the light-emitting states become linearly polarized with maximal polarization of 30.8%, demonstrating a very stable light emission (49,119 cd/m 2 with EQE = 11.31%) and a lower turn-on bias (1.9 V) than the bandgap (2.25V) in the perovskite LEDs (ITO/PEDOT:PSS/MAPbBr 3 /TPBi[50 nm]/LiF[0.7 nm]/Ag). Therefore, mixing large/ small grains with the configuration of attaching small grains on the surfaces of large grains by mixing two precursor solutions presents a new strategy to develop high-performance perovskite LEDs.

Aligning Transition Dipole Moment toward Light Amplification and Polarized Emission in Hybrid Perovskites

“…We follow our previous recipe to develop the perovskite (MAPbBr 3 ) films with mixed large/small grains by using one‐step solution processing method onto the PEDOT:PSS substrate. [ 19,20 ] The resulting perovskites show X‐ray diffraction (XRD) patterns with featured peak at 14.8 0 (corresponding to (100) plane) (Figure S1a, Supporting Information) and an optical bandgap of 2.28 eV (Figure S1b, Supporting Information), consistent with previously reported polycrystalline MAPbBr 3 perovskites. This fabrication procedure enables the controlled passivation of large grains through small grains within one perovskite film.…”

“…This gradual increase of EL intensity suggests the self‐passivation process that the grain boundary defects are slowly passivated during the device operation. [ 19 ] Simultaneously, the relative EL output I 90 / I R measured at polarization direction of 90° gradually increases and stabilizes after around 10 s, which is of the same timescale as self‐passivation process. In contrast, the output I 0 / I R measured at polarization direction of 0° shows negligible change during the EL operation.…”

“…Specifically, the self‐passivation process is verified by continuously increasing EL efficiency at constant bias and the increase of PL quantum efficiency after the poling of the bias. [ 19 ] In order to normalize the continuously variable EL intensity, we design a dual detection method to characterize the DOP of EL through film edge. As shown in Figure a, the light emission is measured simultaneously from perpendicular and parallel directions to device plane.…”

The Role of Grain Boundaries in Charge Carrier Dynamics in Polycrystalline Metal Halide Perovskites

“…To avoid defect induced PL quenching and to improve device performance, the passivation of perovskite films with various additives or self-passivation is performed. [99,100] Very recently Kim et all. simultaneously resolved both challenges using a one-dopant alloying strategy.…”

Carrier Dynamics and Evaluation of Lasing Actions in Halide Perovskites

“…In this equation, the first-order term contains radiative recombination initiated by excitonic emission and/or nonradiative recombination mainly caused by traps, quenchers, or interfacial dissociation [28,29]. In general, the value of a ranges from~10 5 to~10 9 s -1 , mainly extracted from the photoluminescence (PL) lifetime τ at low carrier densities (where a 1 τ ) [30][31][32]. The second-order term, which is also called the bimolecular recombination, contains radiative free electron-hole recombination in 3D perovskites due to their small exciton binding energies [33,34].…”