Unravelling the role of band‐offset landscape on the recombination zone dynamics in perovskite light‐emitting diodes

Abstract

In recent years, impressive progress has been made in developing high‐performance perovskite light‐emitting diodes (PeLEDs) with efficiencies comparable to those of traditional organic light‐emitting diodes (OLEDs). It is convinced that the position of exciton recombination zone is crucial for the performance of the LEDs, however, the dynamics of the exciton recombination zone in PeLEDs and its influence on the performance of PeLEDs remain unclear. Herein, luminescent quantum‐dots (QDs) sensing layers with different energy band landscape and electric properties are introduced into PeLEDs as probers to investigate the position of recombination zone. Consequently, it is found that the band offset between the perovskite layer and the adjacent layer is vital to the position of recombination zone. Modulating the recombination zone towards the bulk of the emission layer helps to improve the device performance as well as the operational stability.

Ligand modification enhanced quantum dot LEDs: principles and methods

“…This stratagy can effectively alleviate exciton bursts and OSI complexes. 21,23,24 The carrier mobility is influenced by ligand exchange that alters the dielectric environment and the tunneling distance between QDs. Mobility typically increases in an exponential fashion with a reduction in ligand length, assuming no other variations.…”

Suppressing Auger Recombination of Perovskite Quantum Dots for Efficient Pure-Blue-Light-Emitting Diodes

“…In principle, the blue emission of perovskites should be achieved easily through perovskite compositional engineering based on the Br/Cl mixed halides, but it suffers from halide segregation issues under an electric field, resulting in much poorer spectral and operational stabilities for the PeLEDs. − Recently, pure-blue PeLEDs based on small bromide-only perovskite QDs with diameters of ∼4 nm were obtained by utilizing the quantum confinement effect, which can avoid the mixed halides issue, thus achieving better operation stability and a continuous operational half-life ( T 50 ) of several hours. − However, the soft and highly ionic lattice structures and low intrinsic formation energies of perovskites lead to ultrafast nucleation and growth rates of the QDs (they form via subsecond fast and hence hard-to-control ionic metathesis reactions). Therefore, it is challenging to obtain strongly confined pure-blue single-bromide perovskite QDs of uniform size and regular shape. , Furthermore, the pure-blue perovskite QDs are a strongly confined system comprising both quantum and dielectric confinement, which leads to the formation of strongly bound excitons and high exciton binding energies ( E b ). , Rapid Auger recombination is proportional to E b because of the enhanced Coulomb electron–hole interaction, which leads to carriers that are no longer uniformly distributed in space, thus raising the probability of finding two electrons and one hole at the same position to accelerate the Auger process, which results in the fast efficiency roll-off for the PeLEDs. − Thus, the EQE of the pure-blue PeLEDs based on QDs is much less than 10%.…”