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Perovskite light-emitting diodes (PeLEDs) have been attracting widespread attention owing to their unique advantages such as high luminance, narrow emission spectra and high color purity. However, the solution-processed fabrication method makes the deposition of multi-emitting layers of perovskite films for white PeLEDs challenging. Moreover, modulating the emission color by adjusting the thickness of the emitting layers will result in reduced optoelectronic performance of the polycrystalline perovskite films. Therefore, strategies for achieving high-performance white PeLEDs are urgently needed. This study developed a newly designed perovskite/organic hybrid tandem light-emitting diode (POTLED) by combining a bottom PeLED unit with a top organic light-emitting diode (OLED) unit. The vacuum deposition process of the OLED avoids damaging the underlying PeLED unit. Additionally, the emission color of the tandem device can be tuned by adjusting the thickness of the organic emitting layer while maintaining the optoelectronic properties of the perovskite layer. As a result, a high-efficiency green POTLED with an outstanding current efficiency of 144.2 cd A−1, an external quantum efficiency of 41.1%, and a luminance of over 32 000 cd m−2 is achieved, illustrating the feasibility and potential of the hybrid tandem perovskite-organic structure to realize high-efficiency white-color perovskite-based devices. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) have shown great potential for low‐cost display and lighting technologies, and all‐inorganic blue PeLEDs are recognized as a promising substitute for blue fluorescent/phosphorescent organic light‐emitting diodes (OLEDs) owing to their superior color purity and great stability potential. However, confined by the solution fabrication process, depositing multi‐layered white PeLEDs remains a challenge. Here, a newly designed hybrid perovskite/organic tandem white LED (POTWLED), integrated with a bottom blue PeLED unit and a top orange/(orange + red) OLED unit, to prevent damage to the underlying perovskite layer caused by the deposition of the top emitting layers, is reported. To optimize the performance of POTWLEDs, a conductive passivator of 2,8‐bis(diphenylphosphoryl)dibenzo[b,d] thiophene, with a strong surface binding group of P═O, is introduced to passivate perovskite defects, which promotes a maximum external quantum efficiency (EQE) of 17.3% for blue PeLEDs with an emission peak at 488 nm. As a result, based on the optimized blue PeLED units, a maximum EQE of 23.9% with a low color temperature of 2522 K is obtained for POTWLEDs, which is the highest efficiency for perovskite‐based WLEDs, illustrating the great potential of the hybrid tandem device in fabricating high‐performance perovskite‐based WLEDs. [ABSTRACT FROM AUTHOR]

Monolithic perovskite/organic tandem solar cells (POTSCs) have significant advantages in next‐generation flexible photovoltaics, owing to their capability to overcome the Shockley–Queisser limit and facile device integration. However, the compromised sub‐cells performance challenges the fabrication of high‐efficiency POTSCs. Especially for all‐inorganic wide‐bandgap perovskite front sub‐cells (AIWPSCs) based n‐i‐p structured POTSCs (AIPOTSCs), for which the power conversion efficiency (PCE) is much lower than organic–inorganic mixed‐halide wide‐bandgap perovskite based POTSCs. Herein, an ionic liquid, methylammonium formate (MAFm), based dual‐interface engineering approach is developed to modify the bottom and top interfaces of wide‐bandgap CsPbI2Br films. In particular, the Fm− group of MAFm can effectively passivate the interface defects, and the top interface modification can facilitate the formation of uniform perovskite films with enlarged grain size, thereby mitigating the defects and perovskite grain boundaries induced carrier recombination. As a result, CsPbI2Br‐based AIWPSCs with a high PCE of 17.0% and open‐circuit voltage (VOC) of 1.347 V are achieved. By integrating these dual‐interface engineered CsPbI2Br‐based front sub‐cells with the narrow‐bandgap PM6:CH1007‐based rear sub‐cells, a record PCE of 23.21% is obtained for AIPOTSCs, illustrating the potential of AIPOTSCs for achieving high‐efficiency tandem solar cells. [ABSTRACT FROM AUTHOR]

Modifications of the surface and interfacial properties of metal halide perovskites (MHPs) have become pivotal strategies in designing high-performance photovoltaics and light-emitting diodes. Particularly, photoelectron spectroscopy (PES) plays a vital role in the advancement of MHP-based optoelectronic devices. Herein, we review the recent studies of PESs for perovskite devices. We first give an overview of the principles of PES and related techniques. Different properties of halide perovskite material unveiled by PES are then discussed, including elemental compositions, chemical states, electronic band structures, interfaces of MHPs and functional layers, ions distribution, and thermal- and moisture-induced degradation mechanism. We also revisit some of the issues when carrying out PES measurements on MHPs, such as irradiation and ambient effects and the uncertainty in determining band edge. Based on these findings, we foresee that PES techniques combined with advanced optical and electron microscopies will become increasingly important to correlate the molecular dynamics with the interfacial and chemical properties of MHP materials and devices. [ABSTRACT FROM AUTHOR]

In addition to mobile and TV displays, there is a trend of organic LEDs being applied in niche markets, such as microdisplays, automobile taillights, and photobiomodulation therapy. These applications mostly do not require to be flexible in form but need to have long operation lifetimes and storage lifespans. Using traditional glass encapsulation may not be able to fulfill the rigorous product specification, and a hybrid encapsulation method by combining glass and thin-film encapsulation will be the solution. Conventional thin-film encapsulation technology generally involves organic and inorganic multilayer films that are thick and have considerable stress. As a result, when subjected to extreme heat and stress, the film easily peels off. Herein, the water vapor transmission rate (WVTR) of a 2 µm silicon nitride film prepared at 85 °C is less than 5 × 10−5 g/m2/day and its stress is optimized to be 23 MPa. Red organic LEDs are passivated with the hybrid encapsulation, and the T95 lifetime reaches nearly 10 years if the LED is continuously driven at an initial luminance of 1000 cd/m2. In addition, a storage lifespan of over 17 years is achieved. [ABSTRACT FROM AUTHOR]

Energy matching between the triplet level of the exciplex hosts and phosphorescent emitters is of particular importance to achieve highly efficient exciplex-based white organic light emitting diodes (WOLEDs). Herein, we design a novel exciplex host and use it for WOLEDs by arranging rational multiple-exciplex hosts in emissive layers. The resulting two-color warm WOLED, by doping blue and orange phosphorescent emitters, shows a maximum forward-viewing power efficiency and external quantum efficiency (EQE) of 104.6 lm W−1 and 30.9%, respectively. Significantly, the EQE still remains 22.1% at 5000 cd m−2. Meanwhile, the three-color warm WOLED has a high color rendering index of over 80 with a maximum EQE of 27.0% and the EQE can remain 21.3% at 5000 cd m−2. These results indicate that rational arrangement of multiple-exciplex hosts in emissive layers is promising for the fabrication of highly efficient WOLEDs. [ABSTRACT FROM AUTHOR]

Luminous efficiency, color purity and spectral stability of white organic light-emitting diodes (WOLEDs) remain the key challenges for display applications based on the "white plus color filter" approach. To tackle these issues, we developed high-efficiency and color-stable WOLEDs in natural color based on all thermally activated delayed fluorescence (TADF) emitters constructed with a blue-orange-blue sandwich emissive layer (EML) structure. The balanced carrier transport and good exciton confinement in this system facilitate excitons broadly forming over the recombination zone and thus realizing a balance of blue and orange emissions in the EMLs successfully. As a result, the device exhibits high-performance pure white emission with the ideal and stable Commission International de I'Eclairage (CIE) coordinates (x, y) of (0.33 ± 0.01, 0.33 ± 0.01) and a high color rendering index (CRI) of 81–83 at a luminance in the range of 250 to 5000 cd m−2. The device shows a maximum external quantum efficiency (EQE) and current efficiency (CE) of 12.0% and 28.0 cd A−1, respectively. The full-TADF WOLEDs with a sandwich EML not only show ideal CIE coordinates and CRIs, but also exhibit excellent color stability. We anticipate that our findings can provide an efficient strategy to realize color stable and high color-purity WOLEDs through the full TADF mechanism and have great potential for display applications. [ABSTRACT FROM AUTHOR]

Metal halide-based perovskites are regarded as promising candidates for light-emitting diodes (LEDs) owing to their high color purity, tunable bandgap and solution processability. However, poor active-layer morphology and non-radiative charge recombination are still the main obstacles for practical use in displays and lighting. Here, we report a facile method to achieve high-performance green emitting perovskite light-emitting diodes (PeLEDs) by inserting an interface buffer layer (BL) based on an amphipathic conjugated molecule, betaine. We show evidence that the betaine layer controls the grain size of the perovskite and hence increases the crystalline nucleation sites, which ultimately leads to a high photoluminescence quantum yield (PLQY) and a device with an external quantum efficiency (EQE) of 11.1%. In addition, the current leakage is significantly reduced due to the high quality crystallization of the thin film. These results indicate that the interface BL is an effective strategy to boost the efficiency of PeLEDs. [ABSTRACT FROM AUTHOR]

All-inorganic halide perovskites with superior optoelectronic properties are promising materials for efficient perovskite light-emitting diodes. However, they usually suffer from a large grain size (hundreds of nanometers), high surface roughness and poor stability during the spin coating process. Here, we report a facile strategy to fabricate a uniform and flat CsPbBr3 film. A small amount of lecithin (LE) introduced into CsPbBr3 precursor solution can promote the formation of small CsPbBr3 grains that remarkably improve the uniformity of perovskite films with a surface roughness of about 2.2 nm. Furthermore, the CsPbBr3–LE films display excellent fluorescence stability in ambient air and LED devices based on the CsPbBr3–5 wt% LE film exhibit a current efficiency (CE) of 24 cd A−1 with an external quantum efficiency (EQE) of 6.5%. Therefore, it is anticipated that the findings of the present study will have great potential to boost the development of PeLEDs. [ABSTRACT FROM AUTHOR]

Hybrid white organic light-emitting diodes (WOLEDs) have drawn great attention both for display and solid-state lighting purposes because of the combined advantages of desirable stability of fluorescent dyes and high efficiency of phosphorescent materials. However, in most WOLEDs, obtaining high efficiency often requires complex device structures. Herein, we achieved high-efficiency hybrid WOLEDs using a simple but efficacious structure, which included a non-doped blue emissive layer (EML) to separate the exciton recombination zone from the light emission region. After optimization of the device structure, the WOLEDs showed a maximum power efficiency (PE), current efficiency (CE), and external quantum efficiency (EQE) of 82.3 lm/W, 70.0 cd/A, and 22.2%, respectively. Our results presented here provided a new option for promoting simple-structure hybrid WOLEDs with superior performance. [ABSTRACT FROM AUTHOR]

Two novel donor-σ-π-σ-acceptor-type dispiro molecules-10-phenyl-10H-dispiro-acridine-9,9'-anthracene-10',9''-fluorene-2'',7''-dicarbo-nitrile (DiSAAF) and dispiro-fluorene-9,9'-anthracene-10',9''-quinolino[3,2,1-kl]phenoxazine-2,7-dicarbonitrile (DiSFAQ)-with excellent thermal stability are designed and synthesized. Both materials exhibit blocked long-range intramolecular charge transfer but show intermolecular charge-transfer emission in the film state. Their photophysical and thermal properties then are fully investigated and a maximum external quantum efficiency of 21.7% of the red phosphorescent device is achieved by DiSAAF.