White light-emitting devices based on ZnCdS/ZnS and perovskite nanocrystal heterojunction

Go beyond the limit: Rationally designed mixed-dimensional perovskite/semiconductor heterostructures and their applications

Halide perovskite heterojunctions rationally integrate the chemical and physical properties of multi-dimensional perovskites and judiciously chosen semiconductor materials, offering the promise of going beyond the limit of a single component. This emerging platform of materials innovation offers fresh opportunities to tune material properties, discover interesting phenomena, and enable novel applications. In this review, we first discuss the fundamentals of forming heterojunctions with perovskites and a wide range of semiconductors, and then we give an overview of the research progress of halide perovskite heterojunctions in terms of their optical, electrical, and mechanical properties, focusing on how the heterojunction tunes the energy band structure, electrical transport, and charge recombination behaviors. We further outline the progress of perovskite-based heterojunctions in optoelectronics. Finally, the challenges and future research directions for perovskite/semiconductor heterojunctions are discussed.

Harvesting the Triplet Excitons of Quasi-Two-Dimensional Perovskite toward Highly Efficient White Light-Emitting Diodes

Utilization of triplet excitons, which generally emit poorly, is always fundamental to realize highly efficient organic light-emitting diodes (LEDs). While triplet harvest and energy transfer via electron exchange between triplet donor and acceptor are fully understood in doped organic phosphorescence and delayed fluorescence systems, the utilization and energy transfer of triplet excitons in quasi-two-dimensional (quasi-2D) perovskite are still ambiguous. Here, we use an orange-phosphorescence-emitting ultrathin organic layer to probe triplet behavior in the sky-blue-emitting quasi-2D perovskite. The delicate white LED architecture enables a carefully tailored Dexter-like energy-transfer mode that largely harvests the triplet excitons in quasi-2D perovskite. Our white organic-inorganic LEDs achieve maximum forward-viewing external quantum efficiency of 8.6% and luminance over 15 000 cd m^-2, exhibiting a significant efficiency enhancement versus the corresponding sky-blue perovskite LED (4.6%). The efficient management of energy transfer between excitons in quasi-2D perovskite and Frenkel excitons in the organic layer opens the door to fully utilizing excitons for white organic-inorganic LEDs.

Perovskite White Light Emitting Diodes: Progress, Challenges, and Opportunities

As global warming, energy shortages, and environment pollution have intensified, low-carbon and energy-saving lighting technology has attracted great attention worldwide. Light emitting diodes (LEDs) have been around for decades and are considered to be the most ideal lighting technology currently due to their high luminescence efficiency (LE) and long lifespan. Besides, along with the development of modern technology, lighting technologies with higher performance and more functions are desired. Perovskite based LEDs (PeLEDs) have recently emerged as ideal candidates for lighting technology owing to the extraordinary photoelectric properties of perovskite, such as high photoluminescence quantum yields (PLQYs), easy wavelength tuning, and low-cost synthesis. Herein, we open this review by introducing the background of white LEDs (WLEDs), including their light-emitting mechanism, typical characteristics, and key indicators in applications. Then, four main approaches to fabricate WLEDs are discussed and compared. After that, in accordance with the four categories, we focus on the recent progress of white PeLEDs (Pe-WLEDs), followed by the challenges and opportunities for Pe-WLEDs in practical application. Meanwhile, some pertinent countermeasures to their challenges are put forward. Finally, the development promise of Pe-WLEDs is explored.

High Color-Rendering Index and Stable White Light-Emitting Diodes by Assembling Two Broadband Emissive Self-Trapped Excitons

White light-emitting diodes (WLEDs) are promising next-generation solid-state light sources. However, the commercialization route for WLED production suffers from challenges in terms of insufficient color-rendering index (CRI), color instability, and incorporation of rare-earth elements. Herein, a new two-component strategy is developed by assembling two broadband emissive materials with self-trapped excitons (STEs) for high CRI and stable WLEDs. The strategy addresses effectively the challenging issues facing current WLEDs. Based on first-principles thermodynamic calculations, copper-based ternary halides composites, CsCu₂ I₃ @Cs₃ Cu₂ I₅ , are synthesized by a facile one-step solution approach. The composites exhibit an ideal white-light emission with a cold/warm white-light tuning and a robust stability against heat, ultraviolet light, and environmental oxygen/moisture. A series of cold/warm tunable WLEDs is demonstrated with a maximum luminance of 145 cd m^-2 and an external quantum efficiency of 0.15%, and a record high CRI of 91.6 is achieved, which is the highest value for lead-free WLEDs. Importantly, the fabricated device demonstrates an excellent operation stability in a continuous current mode, exhibiting a long half-lifetime of 238.5 min. The results promise the use of the hybrids of STEs-derived broadband emissive materials for high-performance WLEDs.