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.
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.
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.
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