Perovskite Light-Emitting Diodes

We look at the development of efficient and stable perovskite light-emitting diodes (PeLEDs) in our lab. Our approach combines fundamental single-particle spectroscopy to understand the intrinsic photophysics of perovskite nanomaterials with innovative device engineering to translate these properties into high-performance electroluminescent devices. This work spans the exploration of lower-dimensional structures and the development of novel composite films that enhance stability without sacrificing efficiency.

Single-Particle Spectroscopy: Uncovering the Photophysics of Lower-Dimensional Perovskites

To design better PeLEDs, an understanding of the emission properties at the level of individual nanocrystals (NCs) is essential. Single-particle spectroscopy (SPS) allows us to probe beyond ensemble averages and uncover heterogeneity and distinct emissive states [1]. SPS studies of zero-dimensional (0D) perovskites like Cs₄PbBr₆ reveal that their bright luminescence originates from individual, molecular-like emissive sites within each nanocrystal, often associated with specific defect states (e.g., bromine vacancies) [1]. This is in contrast to three-dimensional (3D) CsPbBr₃ NCs, which typically behave as single, unified emitters. Understanding that 0D perovskites are ensembles of independent emitters helps explain their high photoluminescence quantum yield (PLQY) and provides a roadmap for optimizing their synthesis. By controlling defect formation, we can directly influence the efficiency of the light-emitting material that will be used in a device [1].

Engineering Stable and Efficient 0D/3D Composite Emissive Layers

A major challenge for PeLEDs is operational stability. While 3D CsPbBr₃ perovskites offer excellent charge transport, they can be susceptible to degradation. Conversely, 0D Cs₄PbBr₆ structures are highly stable but are electrical insulators. A hybrid approach combines the best of both worlds [2]. A stable and bright electroluminescent device is created by incorporating emissive 0D perovskite nanocrystals directly into a thin-film matrix of 3D CsPbBr₃ [2]. In this architecture, the robust 0D NCs act as the primary light-emitting centers, while the 3D matrix provides an efficient pathway for electrical charge injection and transport. This 0D/3D composite structure resulted in PeLEDs with significantly improved operational stability compared to standard 3D perovskite devices. The devices maintained bright electroluminescence over extended periods, demonstrating that the stable 0D emitters are effectively protected and powered by the surrounding 3D matrix [2]. This strategy decouples the requirements of charge transport and light emission, enabling the use of highly luminescent but otherwise insulating materials in efficient LEDs.

Developing Novel Red-Emissive Materials for Expanded Color Gamut

For display applications, stable red emitters are crucial. The 0D perovskite platform was extended to mixed-halide iodide systems to access the red spectral range [3]. We synthesized highly emissive and photostable 0D Cs₄Pb(Br₀.₂₅I₀.₇₅)₆ nanocrystals with a PLQY of ~40%. The partial incorporation of bromide was critical to enhancing the stability of the typically fragile iodide-based perovskite structure, making it suitable for optoelectronic studies and applications [3]. Single-particle analysis of these red-emitting 0D NCs revealed a unique thermally activated delayed photoluminescence. At room temperature, defect states act as “charge reservoirs,” slowly feeding energy back to the emissive site and resulting in long-lived emission components (up to 70 ns) and multi-photon emission statistics [3]. This understanding of the charge dynamics in 0D iodide systems informs how these materials would behave under electrical injection in a LED. Managing these defect-related processes is key to maximizing efficiency and achieving pure color emission for red PeLEDs.

Work on PeLEDs demonstrates understanding of using single-particle spectroscopy to decode the complex photophysics of lower-dimensional perovskite emitters, from defect-related luminescence in 0D systems to charge trapping dynamics [1, 3]. It’s led to material innovation in designing new materials, such as mixed-halide 0D NCs, that combine high PLQY with improved environmental stability [3] and inventing novel device architectures, like the 0D-in-3D composite film, which leverages the respective strengths of different perovskite dimensionalities to achieve both high efficiency and excellent operational stability in working LEDs [2]. This integrated approach, moving from single-particle insights to functional devices, drive progress toward the commercialization of perovskite-based lighting and displays.

[1] Bose, R. et al. Single-Particle Spectroscopy as a Versatile Tool to Explore Lower-Dimensional Structures of Inorganic Perovskites. ACS Energy Lett. 2021, *6* (10), 3695–3708. DOI: 10.1021/acsenergylett.1c01604

[2] Mishra, A. et al. Stable and Bright Electroluminescent Devices Utilizing Emissive 0D Perovskite Nanocrystals Incorporated in a 3D CsPbBr₃ Matrix. Adv. Mater. 2022, *34*, 2203226. DOI: 10.1002/adma.202203226

[3] Zhou, X. et al. Highly Emissive Zero-Dimensional Cesium Lead Iodide Perovskite Nanocrystals with Thermally Activated Delayed Photoluminescence. J. Phys. Chem. Lett. 2023, *14* (12), 2933–2939. DOI: 10.1021/acs.jpclett.3c00219