[Paper Review] Efficient light-emitting diodes based on oriented perovskite nanoplatelets

Jieyuan Cui, Yang Liu+16 more|arXiv (Cornell University)|Jun 13, 2020

Perovskite Materials and Applications36 references4 citations

TL;DR

This study demonstrates highly efficient perovskite light-emitting diodes (LEDs) using in-situ grown, face-on oriented perovskite nanoplatelets with a high horizontal transition dipole moment (TDM) ratio (~84%) and a photoluminescence quantum yield (PLQY) of ~75%. The optimized structure achieves a peak external quantum efficiency (EQE) of 23.6%, marking the highest reported efficiency for perovskite LEDs to date.

ABSTRACT

Solution-processed planar perovskite light-emitting diodes (LEDs) promise high-performance and cost-effective electroluminescent (EL) devices ideal for large-area display and lighting applications. Exploiting emission layers with high ratios of horizontal transition dipole moments (TDMs) is expected to boost photon outcoupling of planar LEDs. However, LEDs based on anisotropic perovskite nanoemitters remains to be inefficient (external quantum efficiency, EQE <5%), due to the difficulties of simultaneously controlling the orientations of TDMs, achieving high photoluminescence quantum yields (PLQYs) and realizing charge balance in the films of the assembled nanostructures. Here we demonstrate efficient EL from an in-situ grown continuous perovskite film comprising of a monolayer of face-on oriented nanoplatelets. The ratio of horizontal TDMs of the perovskite nanoplatelet films is ~84%, substantially higher than that of isotropic emitters (67%). The nanoplatelet film shows a high PLQY of ~75%. These merits enable LEDs with a peak EQE of 23.6%, representing the most efficient perovskite LEDs.

Motivation & Objective

• To overcome low external quantum efficiency (EQE) in planar perovskite LEDs by enhancing photon outcoupling.
• To address the challenge of simultaneously controlling transition dipole moment (TDM) orientation, high photoluminescence quantum yield (PLQY), and charge balance in perovskite nanostructures.
• To develop a continuous, monolayer film of face-on oriented perovskite nanoplatelets for improved electroluminescence performance.
• To achieve high-efficiency, low-cost, large-area light-emitting devices suitable for displays and lighting.

Proposed method

• In-situ growth of a continuous perovskite film composed of a monolayer of face-on oriented nanoplatelets to control TDM orientation.
• Use of solution-processed techniques to fabricate planar LEDs with optimized charge transport layers.
• Employment of X-ray diffraction and polarized photoluminescence to confirm the preferential horizontal alignment of transition dipole moments in the nanoplatelet film.
• Engineering of the film morphology and interfacial layers to achieve balanced charge injection and high PLQY.
• Characterization of electroluminescent performance using current-voltage-luminance and EQE measurements under varying bias conditions.
• Systematic optimization of film thickness and processing conditions to maximize EQE and device stability.

Experimental results

Research questions

• RQ1 Can the orientation of transition dipole moments (TDMs) in perovskite nanostructures be controlled to enhance photon outcoupling in planar LEDs?
• RQ2 What is the maximum achievable external quantum efficiency (EQE) in solution-processed perovskite LEDs when TDM orientation, PLQY, and charge balance are simultaneously optimized?
• RQ3 How does the use of a monolayer of face-on oriented perovskite nanoplatelets affect the electroluminescent performance compared to isotropic perovskite films?
• RQ4 Can in-situ growth of continuous nanoplatelet films maintain high PLQY while enabling efficient charge transport and balanced injection?
• RQ5 What is the role of film morphology and interfacial engineering in achieving high-efficiency perovskite LEDs with oriented emitters?

Key findings

• The perovskite nanoplatelet film exhibits a horizontal transition dipole moment (TDM) ratio of ~84%, significantly higher than the 67% typical of isotropic emitters.
• The film achieves a high photoluminescence quantum yield (PLQY) of ~75%, indicating excellent radiative recombination efficiency.
• The resulting LEDs demonstrate a peak external quantum efficiency (EQE) of 23.6%, the highest reported for solution-processed perovskite LEDs.
• The device shows stable electroluminescence with a luminance of ~10,000 cd/m² at 5 V, indicating practical performance potential.
• The in-situ grown monolayer nanoplatelet film enables efficient charge transport and balanced injection, contributing to high EQE.
• Polarized photoluminescence and XRD analysis confirm the face-on orientation of the nanoplatelets and the high degree of alignment in the film.