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The morphological characteristics of in‐situ‐grown perovskite thin films are strongly influenced by the interface properties of previous layer. Additionally, their photoelectric characteristics are closely tied to the formed defects during the solution‐processing film for the oxidized tin ions, which significantly hinders the practicality of tin‐based perovskites in near‐infrared light‐emitting diodes (LEDs). Here, formamidine thiocyanate is employed to modify the interfacial behaviors of hole transport layer under the perovskite layer, resulting in reduced contact angle, improved surface wettability, enhancement of the crystallinity and film quality of tin‐based perovskite. Furthermore, by introducing guanidine thiocyanate into the precursor solution, the oxidation is successfully suppressed during the film formation of tin‐based perovskite, thereby reducing film defects to suppress non‐radiative recombination. A near‐infrared LEDs with a maximum external quantum efficiency reached 5.1%, representing a twofold improvement compared to unmodified devices. This advancement holds significant implications for the progression of tin‐based near‐infrared light emission technology. [ABSTRACT FROM AUTHOR]

Even though lead halide perovskite has been demonstrated as a promising optoelectronic material for next-generation display applications, achieving high-efficiency and stable pure-red (620~635 nm) emission to cover the full visible wavelength is still challenging. Here, we report perovskite light-emitting diodes emitting pure-red light at 628 nm achieving high external quantum efficiencies of 26.04%. The performance is attributed to successful synthesizing strongly confined CsPbI3 quantum dots with good stability. The strong binding 2-naphthalene sulfonic acid ligands are introduced after nucleation to suppress Ostwald ripening, meanwhile, ammonium hexafluorophosphate exchanges long chain ligands and avoids regrowth by strong binding during the purification process. Both ligands enhance the charge transport ability of CsPbI3 quantum dots. The state-of-the-art synthesis of pure red CsPbI3 quantum dots achieves 94% high quantum efficiency, which can maintain over 80% after 50 days, providing a method for synthesizing stable strong confined perovskite quantum dots. Li et al. report the regulation of perovskite quantum dot growth after nucleation by designing ligand exchange utilising proton transfer. The Ostwald ripening and regrowth are prohibited with an external quantum efficiency of 26.04% achieved in the pure-red perovskite light-emitting diodes. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) based on quasi‐2D perovskites have attracted great attention in the past few years. Although significant achievements are made in device performance, fabrication of high‐efficiency PeLEDs with pure‐red (620–635 nm) light emission remains a significant challenge, which inhibits their practical application for full‐color displays. Herein, a series of efficient red PeLEDs at 625 nm are realized by employing volatile alkylammonium chlorides (propylammonium chloride) passivators. The interaction of PbI2 with propylamine (PA)...H+Cl− in the precursor solution effectively passivates the defects, leading to reduced non‐radiative recombination and enhanced device performance. By optimizing the amount of PACl, an external quantum efficiency (EQE) of 16.1% and a maximum brightness of 1701 cd m−2 are achieved, among the best‐performing quasi‐2D I‐based PeLEDs with emissions ranging from 620 to 635 nm. This work provides a new route to improve the stability and efficiency of pure‐red PeLEDs. [ABSTRACT FROM AUTHOR]

Poly(3,4-ethylene dioxythiophene)/poly(styrene sulfonic acid), abbreviated as PEDOT:PSS, is widely used in light-emitting diodes, solar cells, sensors, and other functional devices due to its high conductivity, transparency, and solution processability. In this study, the photo-reactive cross-linking agent 2,4-hexadiyne-1,6-diol (HOD) was introduced for a comparative study of photo-crosslinking in PEDOT:PSS AI 4083 (denoted as 4083) and PEDOT:PSS PH1000 (denoted as PH1000). The results showed that the aggregation state of 4083 was different from that of PH1000, ascribed to the composition of 4083 and PH1000 and the mechanism of the photo-crosslinking agent. Based on these findings, quantum dot light-emitting diode (QLED) devices were fabricated using direct photo-crosslinking PH1000. The work function based on PH1000 as a hole-injected layer (HIL) was increased from 5.03 eV to 5.22 eV, and the external quantum efficiency (EQE) was increased from 17.2% to 18.9%. This result provided a feasible solution for the application of PH1000 in high-performance QLED displays. [ABSTRACT FROM AUTHOR]

Highlights: A new proton-promoted in situ ligand exchange strategy based on CsPbI3 quantum dots. The ligand exchange strategy maintains the quantum confinement effect of quantum dots and significantly improves the stability and photophysical properties of CsPbI3 quantum dots. The performance of light-emitting diodes based on CsPbI3 quantum dots is significantly improved, the external quantum efficiency is increased from 18.63% to 24.45%, and the half-operational lifetime is increased by 70 times. CsPbI3 perovskite quantum dots (QDs) are ideal materials for the next generation of red light-emitting diodes. However, the low phase stability of CsPbI3 QDs and long-chain insulating capping ligands hinder the improvement of device performance. Traditional in-situ ligand replacement and ligand exchange after synthesis were often difficult to control. Here, we proposed a new ligand exchange strategy using a proton-prompted in-situ exchange of short 5-aminopentanoic acid ligands with long-chain oleic acid and oleylamine ligands to obtain stable small-size CsPbI3 QDs. This exchange strategy maintained the size and morphology of CsPbI3 QDs and improved the optical properties and the conductivity of CsPbI3 QDs films. As a result, high-efficiency red QD-based light-emitting diodes with an emission wavelength of 645 nm demonstrated a record maximum external quantum efficiency of 24.45% and an operational half-life of 10.79 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • WS 2 was used as the hole interface layer to improve the hole transport ability through energy level matching. • The crystal quality of perovskite film was improved by using WS 2 as the hole interface layer. • Obtained high-performance Quasi-2D blue perovskite light-emitting devices with EQE of 3.24%. Due to the deep energy levels, the external quantum efficiency (EQE) of the blue perovskite light-emitting diode (PeLED) is far lower than its green, red, and near-infrared counterparts, which has exceeded 20%. The mismatched energy levels between perovskites and the hole transporting layer (HTL) still hinder the hole injection and consequent improvement of blue PeLED device performance. Here, a two-dimensional material, WS 2 (Tungsten disulfide), was introduced to match the energy levels between perovskites and HTL and enhanced the hole injection. The WS 2 HTL-based perovskite FAPbBr 3-x Cl x blue LED achieved a luminance of 990 cd/m2 with an EQE of 3.24%, which surpasses the performance of previously reported for the formamidinium (FA) based system, indicating the potential of WS 2 for PeLEDs. [ABSTRACT FROM AUTHOR]