Efficient Ruddlesden-Popper Perovskite Light-Emitting Diodes with Randomly Oriented Nanocrystals

Ruddlesden-Popper phase (RP-phase) perovskites that consist of 2D perovskite slabs interleaved with bulky organic ammonium (OA) are favorable for light-emitting diodes (LEDs). The critical limitation of LED applications is that the insulating OA arranged in a preferred orientation limits charge transport. Therefore, the ideal solution is to achieve a randomly connected structure that can improve charge transport without hampering the confinement of the electron-hole pair. Here, a structurally modulated RP-phase metal halide perovskite (MHP), (PEA)(2)(CH3NH3)(m-1)PbmBr3m+1 is introduced to make the randomly oriented RP-phase unit and ensure good connection between them by applying modified nanocrystal pinning, which leads to an increase in the efficiency of perovskite LEDs (PeLEDs). The randomly connected RP-phase MHP forces contact between inorganic layers and thereby yields efficient charge transport and radiative recombination. Combined with an optimal dimensionality, (PEA)(2)(CH3NH3)(2)Pb3Br10, the structurally modulated RP-phase MHP exhibits increased photoluminescence quantum efficiency, from 0.35% to 30.3%, and their PeLEDs show a 2,018 times higher current efficiency (20.18 cd A(-1)) than in the 2D PeLED (0.01 cd A(-1)) and 673 times than in the 3D PeLED (0.03 cd A(-1)) using the same film formation process. This approach provides insight on how to solve the limitation of RP-phase MHP for efficient PeLEDs.

Efficient Perovskite Light-Emitting Diodes Using Polycrystalline Core-Shell-Mimicked Nanograins

Making small nanograins in polycrystalline organic-inorganic halide perovskite (OIHP) films is critical to improving the luminescent efficiency in perovskite light-emitting diodes (PeLEDs). 3D polycrystalline OIHPs have fundamental limitations related to exciton binding energy and exciton diffusion length. At the same time, passivating the defects at the grain boundaries is also critical when the grain size becomes smaller. Molecular additives can be incorporated to shield the nanograins to suppress defects at grain boundaries; however, unevenly distributed molecular additives can cause imbalanced charge distribution and inefficient local defect passivation in polycrystalline OIHP films. Here, a kinetically controlled polycrystalline organic-shielded nanograin (OSN) film with a uniformly distributed organic semiconducting additive (2,2 ',2 ''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole), TPBI) is developed mimicking core-shell nanoparticles. The OSN film causes improved photophysical and electroluminescent properties with improved light out-coupling by possessing a low refractive index. Finally, highly improved electroluminescent efficiencies of 21.81% ph el(-1) and 87.35 cd A(-1) are achieved with a half-sphere lens and four-time increased half-lifetime in polycrystalline PeLEDs. This strategy to make homogeneous, defect-healed polycrystalline core-shell-mimicked nanograin film with better optical out-coupling will provide a simple and efficient way to make highly efficient perovskite polycrystal films and their optoelectronics devices.

Advances in solution-processed near-infrared light-emitting diodes

Near-infrared light-emitting diodes based on solution-processed semiconductors, such as organics, halide perovskites and colloidal quantum dots, have emerged as a viable technological platform for biomedical applications, night vision, surveillance and optical communications. The recently gained increased understanding of the relationship between materials structure and photophysical properties has enabled the design of efficient emitters leading to devices with external quantum efficiencies exceeding 20%. Despite considerable strides made, challenges remain in achieving high radiance, reducing efficiency roll-off and extending operating lifetime. This Review summarizes recent advances on emissive materials synthetic methods and device key attributes that collectively contribute to improved performance of the fabricated light-emitting devices

Phosphine Oxide Derivative as a Passivating Agent to Enhance the Performance of Perovskite Solar Cells

Defects of metal-halide perovskites detrimentally influence the optoelectronic properties of the thin film and, ultimately, the photovoltaic performance of perovskite solar cells (PSCs). Especially, defect-mediated nonradiative recombination that occurs at the perovskite interface significantly limits the power conversion efficiency (PCE) of PSCs. In this regard, interfacial engineering or surface treatment of perovskites has become a viable strategy for reducing the density of surface defects, thereby improving the PCE of PSCs. Here, an organic molecule, tris(5-((tetrahydro-2H-pyran-2-yl)oxy)pentyl)phosphine oxide (THPPO), is synthesized and introduced as a defect passivation agent in PSCs. The P=O terminal group of THPPO, a Lewis base, can passivate perovskite surface defects such as undercoordinated Pb2+. Consequently, improvement of PCEs from 19.87 to 20.70% and from 5.84 to 13.31% are achieved in n−i−p PSCs and hole-transporting layer (HTL)-free PSCs, respectively

Au–Ag assembled on silica nanoprobes for visual semiquantitative detection of prostate-specific antigen

Background Blood prostate-specific antigen (PSA) levels are widely used as diagnostic biomarkers for prostate cancer. Lateral-flow immunoassay (LFIA)-based PSA detection can overcome the limitations associated with other methods. LFIAbased PSA detection in clinical samples enables prognosis and early diagnosis owing to the use of high-performance signal reporters. Results Here, a semiquantitative LFIA platform for PSA detection in blood was developed using Au–Ag nanoparticles (NPs) assembled on silica NPs (SiO2@Au–Ag NPs) that served as signal reporters. Synthesized SiO2@Au–Ag NPs exhibited a high absorbance at a wide wavelength range (400–800 nm), with a high scattering on nitrocellulose membrane test strips. In LFIA, the color intensity of the test line on the test strip differed depending on the PSA concentration (0.30–10.00 ng/mL), and bands for the test line on the test strip could be used as a standard. When clinical samples were assessed using this LFIA, a visual test line with particular color intensity observed on the test strip enabled the early diagnosis and prognosis of patients with prostate cancer based on PSA detection. In addition, the relative standard deviation of reproducibility was 1.41%, indicating high reproducibility, and the signal reporter showed good stability for 10 days. Conclusion These characteristics of the signal reporter demonstrated the reliability of the LFIA platform for PSA detection, suggesting potential applications in clinical sample analysis.This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF2020R1F1A1072702). This study was also supported by the WTU Joint Research Grant of Konkuk University in 2017 (2017-A019-0334)

Proton-transfer-induced 3D/2D hybrid perovskites suppress ion migration and reduce luminance overshoot

Abstract: Perovskite light-emitting diodes (PeLEDs) based on three-dimensional (3D) polycrystalline perovskites suffer from ion migration, which causes overshoot of luminance over time during operation and reduces its operational lifetime. Here, we demonstrate 3D/2D hybrid PeLEDs with extremely reduced luminance overshoot and 21 times longer operational lifetime than 3D PeLEDs. The luminance overshoot ratio of 3D/2D hybrid PeLED is only 7.4% which is greatly lower than that of 3D PeLED (150.4%). The 3D/2D hybrid perovskite is obtained by adding a small amount of neutral benzylamine to methylammonium lead bromide, which induces a proton transfer from methylammonium to benzylamine and enables crystallization of 2D perovskite without destroying the 3D phase. Benzylammonium in the perovskite lattice suppresses formation of deep-trap states and ion migration, thereby enhances both operating stability and luminous efficiency based on its retardation effect in reorientation

Charge carrier recombination and ion migration in metal-halide perovskite nanoparticle films for efficient light-emitting diodes

Metal-halide perovskite (MHP) nanoparticles (NPs) have attracted considerable attention as a promising light emitter for efficient light-emitting diodes (LEDs) due to their high color-purity and photoluminescence quantum efficiency (PLQE). In contrast to MHP polycrystalline (PC) bulk films, charge carrier recombination as well as ion migration dynamics in MHP NP films have not been studied yet despite the importance to achieve high electroluminescence efficiency in LEDs. Here, we use steady-state and transient photoluminescence measurements, and photo-responsivity analysis to study the charge carrier recombination and ion migration dynamics in MHP NP films and then, compare these with those of MHP PC films. Results show that MHP NP films do not undergo the severe ion migration and have dominant radiative recombination of excitons by efficiently confining electron-hole pairs. As a result, MHP NP films have high photo-stability, photo-responsibility, and PLQE (> 60%). Our findings provide insight into charge carrier and ion dynamics in MHP NP films, and confirm the potential of NP films for use in efficient LEDs.

Planar heterojunction organometal halide perovskite solar cells: roles of interfacial layers

Organometal halide perovskites are promising photo-absorption materials in solar cells due to their high extinction coefficient, broad light absorption range and excellent semiconducting properties. The highest power conversion efficiency (PCE) of perovskite solar cells (PrSCs) is now 20.1%. However, a high-temperature processed mesoscopic metal oxide (e.g., TiO2) must be removed to realize flexible PrSCs on plastic substrates using low temperature processes. Although the planar heterojunction (PHJ) structure can be considered as the most appropriate structure for flexible PrSCs, they have shown lower PCEs than those with a mesoscopic metal oxide layer. Therefore, development of interfacial layers is essential for achieving highly efficient PHJ PrSCs, and necessary in fabrication of flexible PrSCs. This review article gives an overview of progress in PHJ PrSCs and the roles of interfacial layers in the device, and suggests a practical strategy to fabricate highly efficient and flexible PHJ PrSCs. We conclude with our technical suggestion and outlook for further research direction.11206164sciescopu

Graphene-based flexible electronic devices

Flexible electronic devices fabricated on plastic substrate are more desirable than rigid counterparts for future displays, lightings, or solar cells. For flexible electronics to become practical, the indium-tin-oxide (ITO) electrode should be replaced due to its brittleness, increasing cost, and chemical instability. Graphene has emerged as a promising material for flexible transparent conducting electrodes because-of its unique electronic and mechanical properties with high optical transmittance. Therefore, graphene has been widely used in flexible electronic devices including light-emitting diodes (LEDs), solar cells (SCs), and field-effect transistors (FETs). However, for practical applications-of graphene in flexible electronics, its limitations should also be overcome. This review describes the use of graphene in LEDs, SCs and FETs, and various strategies to overcome the deficiencies of graphene to obtain highly-efficient and stable flexible electronics. Finally, we present future prospects and suggest further directions for research On graphene-based flexible electronic devices. (C) 2017 Elsevier B.V. All rights reserved.