KEYWORDS: 3D printing, Printing, Voxels, Photonics, Nonimpact printing, Digital micromirror devices, 3D applications, Upconversion, Two photon polymerization, Spatial resolution
Nanoscale 3D printing enables a wide variety of applications from photonics to biology. Specifically, using a DMD to project light into a triplet fusion upconversion 3D printing resin can allow rapid printing. This requires selecting a single plane at a time. However, as an image is projected into the resin, the z-resolution of the printing system can be limited by substantial light intensity around the focal plane. Using a home-built setup, we study how we can manipulate the images uploaded to the DMD to optimize the resolution of our prints. We present our findings towards high-resolution nanoscale volumetric 3D printing.
In this work, we dope Mn2+ ions into an organic-inorganic hybrid quasi-bulk 3D perovskite with the addition of tris(4-fluorophenyl)phosphine oxide (TFPPO) dissolved in a chloroform antisolvent to achieve green perovskite LEDs (PeLEDs) with a 14.0% EQE and a 128,000 cd/m2 peak luminance. While TFPPO dramatically increases the PeLEDs’ EQE, the operational stability is compromised. At 5mA/cm2, our PeLED fabricated with a pure chloroform antisolvent (EQE=2.97%) decays to half of its maximum luminance in 37.0 minutes. Alternatively, our PeLED fabricated with TFPPO (EQE=14.0%) decays in 2.54 minutes. Consequently, we studied both photophysical and optoelectronic characteristics before and after PeLED electrical degradation.
Metal halide perovskites (MHPs) have established their prominence in the field of optoelectronics, exhibiting considerable potential for use in light-emitting diodes (LEDs) spanning the red, green, blue, and even near-infrared spectra. Despite this, the exploration of MHPs within the ultraviolet light emission domain remains comparatively underexplored. In this study, we exploit the inherent versatility of perovskite composition and dimensionality to address this research gap. By integrating long organic ligands and mixed halides, we fabricate two-dimensional (2D) MHP thin films capable of achieving a diverse range of bandgaps within the ultraviolet region. To enhance the coverage of these thin films, we introduce water-based additives and a two-step annealing process into the fabrication protocol. A variety of analytical techniques, including absorption and photoluminescence spectra analysis, along with atomic force microscopy, were employed to characterize these 2D perovskite thin films. Our findings underscore the vast potential of MHPs for ultraviolet light-emitting diodes. This work is aimed at inspiring further investigations in this promising yet under-studied domain, paving the way for novel advancements in realization of bright and efficient ultraviolet emitting technology.
KEYWORDS: Upconversion, Photons, External quantum efficiency, Solid state physics, Solid state electronics, Quantum processes, Quantum devices, Photovoltaics, Night vision, Energy transfer
Upconversion (UC) of NIR photons into visible photons can improve photovoltaics technologies and enable passive night vision. However, current solid-state triplet-triplet annihilation UC devices suffer from low absorption, low energy transfer rates, and highly parasitic back transfer processes which lead to low external quantum efficiencies (EQE). We propose the introduction of a “blocker layer” which can mitigate FRET-based back transfer to improve the EQE. We demonstrate the use of 5-tetracene carboxylic acid (TCA) as a ligand/blocker layer to improve EQE by 3-5x. Finally, we deconvolve the mechanism of improvement through spectroscopic comparison of the traditional and our novel UC devices.
Volumetric 3D printing has tremendous potential due to its ability to print in static resin vats and produce complicated parts without support structures, and two-photon printing has been tremendously successful in this regard. Here, we utilize a molecular form of upconversion, triplet fusion, to achieve the same quadratic light dependence as two photon absorption at much lower powers. We demonstrate the ability to tune the upconversion threshold across two orders of magnitude and encapsulate the molecules at the nanoscale, providing durability upon addition to a resin. These materials allow us to volumetrically print with less than 4 mW of CW laser power. In this talk we will also discuss future directions of this technology.
Using transient optical spectroscopies, we study excitation recombination dynamics in manganese-doped cesium lead-halide perovskite nanocrystals. Unexpectedly, we find an increase in the intrinsic excitonic radiative recombination rate upon doping, which is typically a challenging material property to tailor. Supported by ab initio calculations, we can attribute the enhanced emission rates to increased exciton localization through lattice periodicity breaking from Mn dopants, which increases exciton effective masses and overlap of electron and hole wavefunctions and thus the oscillator strength. Our report of a fundamental strategy for improving luminescence efficiencies in perovskite nanocrystals will be valuable for maximizing efficiencies in light-emitting applications.
Singlet fission can split a high energy singlet exciton and generate two lower energy triplet excitons. This process has shown near 200 percent triplet exciton yield. Sensitizing solar cells with singlet fission material, it can potentially increase the power conversion efficiency limit from 29 percent to 35 percent. Singlet fission in the tetracene is known to be efficient, and the energy of the triplet excitons are energetically matched to the silicon bandgap. In this work, we designed an optical measurement with an external magnetic field to determine the efficiencies of triplet exciton transfer from tetracene to silicon. Using this method, we have found that a passivation layer of 8 angstroms of hafnium oxynitride on silicon allows efficient triplet exciton transfer around 133 percent.
Blue nanocrystal perovskite LEDs have traditionally lagged behind their red and green cousins. Here, we discuss the reasons for this lag and propose solutions to these problems, producing high efficiency blue perovskite LEDs. We demonstrate the NiOx, a transport material in one of the highest performing devices to date, reduces the performance of nanocrystals near to the interface. By replacing it with an alternative transport structure, we show that the nanocrystal emission is unperturbed. We then build full LEDs out of this transport structure, increasing the EQE from 0.03% to 0.50%, the highest for inorganic perovskite nanocrystals at this wavelength. We further show that the benefits of this transport structure relax as the energetics redshift, as our blue-green devices match those from literature. These results are a useful step forward towards commercially relevant perovskite LEDs.
Organic-inorganic perovskites have revolutionized the optoelectronics field, providing materials with a wide range of properties for solving numerous applications. Indeed, much recent work has been focused on nanostructured perovskites, with quantum dots, nanowires, and nanoplatelets showing tremendous potential. Here, we utilize the unique tunability of 2D perovskite nanoplatelets to build LEDs that span the visible spectrum. Quantum confinement in the z direction drives a significant blueshift, allowing for blue devices utilizing the bromide system and orange devices utilizing the iodide system. We demonstrate that excess ligand addition is crucial to achieving this blueshift in thin films that otherwise suffer from energy funneling. We build devices that show electroluminescence from 440 nm to 650 nm, although they still suffer from low efficiencies due to low photoluminescence quantum yields. We finally demonstrate that these materials suffer from reversible degradation with an applied electric field, further limiting the efficiency. The favorable optoelectronic properties of perovskite materials, combined with the blueshift due to quantum confinement, shows the promise of these materials as a new class of low cost emitters.
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