Title: Phase segregation in inorganic mixed-halide perovskites: from phenomena to mechanisms
Halide perovskites, such as methylammonium lead halide perovskites (,, Br, and Cl), are emerging as promising candidates for a wide range of optoelectronic applications, including solar cells, light-emitting diodes, and photodetectors, due to their superior optoelectronic properties. All-inorganic lead halide perovskitesare attracting a lot of attention because replacing the organic cations withenhances the stability, and its halide-mixing derivatives offer broad bandgap tunability covering nearly the entire visible spectrum. However, there is evidence suggesting that the optical properties of mixed-halide perovskites are influenced by phase segregation under external stimuli, especially illumination, which may negatively impact the performance of optoelectronic devices. It is reported that the mixed-halide perovskites in forms of thin films and nanocrystals are segregated into a low-bandgap I-rich phase and a high-bandgap Br-rich phase. Herein, we present a critical review on the synthesis and basic properties of all-inorganic perovskites, phase-segregation phenomena, plausible mechanisms, and methods to mitigate phase segregation, providing insights on advancing mixed-halide perovskite optoelectronics with reliable performance.
A novel characterization method is proposed to extract the optical frequency field-effect mobility () of transparent conductive oxide (TCO) materials by a tunable silicon microring resonator with a heterogeneously integrated titanium-doped indium oxidemetal–oxide–semiconductor (MOS) capacitor. By operating the microring in the accumulation mode, the quality factor and resonance wavelength shift are measured and subsequently used to derive thein the ultra-thin accumulation layer. Experimental results demonstrate that theof ITiO increases from 25.3 towith increasing gate voltages, which shows a similar trend as that at the electric frequency.
Brown, Ei_Ei; Fleischman, Zackery_D; McKay, Jason; Hommerich, Uwe; Kabir, Al_Amin; Riggins, Jazmine; Trivedi, Sudhir; Dubinskii, Mark(
, Journal of the Optical Society of America B)
The mid-IR spectroscopic properties ofdoped low-phononandcrystals grown by the Bridgman technique have been investigated. Using optical excitations atand, both crystals exhibited IR emissions at,,, andat room temperature. The mid-IR emission at 4.5 µm, originating from thetransition, showed a long emission lifetime offordoped, whereasdopedexhibited a shorter lifetime of. The measured emission lifetimes of thestate were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulated emission cross sections for thetransition indopedandwere determined to beand, respectively. The results of Judd–Ofelt analysis are presented and discussed.
Amorphous tantala () thin films were deposited by reactive ion beam sputtering with simultaneous low energy assistorbombardment. Under the conditions of the experiment, the as-deposited thin films are amorphous and stoichiometric. The refractive index and optical band gap of thin films remain unchanged by ion bombardment. Around 20% improvement in room temperature mechanical loss and 60% decrease in absorption loss are found in samples bombarded with 100-eV. A detrimental influence from low energybombardment on absorption loss and mechanical loss is observed. Low energybombardment removes excess oxygen point defects, whilebombardment introduces defects into the tantala films.
In Part I [Appl. Opt.58,6067(2019)APOPAI003-693510.1364/AO.58.006067], we used a coupled optoelectronic model to optimize a thin-film(CIGS) solar cell with a graded-bandgap photon-absorbing layer and a periodically corrugated backreflector. The increase in efficiency due to the periodic corrugation was found to be tiny and that, too, only for very thin CIGS layers. Also, it was predicted that linear bandgap-grading enhances the efficiency of the CIGS solar cells. However, a significant improvement in solar cell efficiency was found using a nonlinearly (sinusoidally) graded-bandgap CIGS photon-absorbing layer. The optoelectronic model comprised two submodels: optical and electrical. The electrical submodel applied the hybridizable discontinuous Galerkin (HDG) scheme directly to equations for the drift and diffusion of charge carriers. As our HDG scheme sometimes fails due to negative carrier densities arising during the solution process, we devised a new, to the best of our knowledge, computational scheme using the finite-difference method, which also reduces the overall computational cost of optimization. An unfortunate normalization error in the electrical submodel in Part I came to light. This normalization error did not change the overall conclusions reported in Part I; however, some specifics did change. The new algorithm for the electrical submodel is reported here along with updated numerical results. We re-optimized the solar cells containing a CIGS photon-absorbing layer with either (i) a homogeneous bandgap, (ii) a linearly graded bandgap, or (iii) a nonlinearly graded bandgap. Considering the meager increase in efficiency with the periodic corrugation and additional complexity in the fabrication process, we opted for a flat backreflector. The new algorithm is significantly faster than the previous algorithm. Our new results confirm efficiency enhancement of 84% (resp. 63%) when the thickness of the CIGS layer is 600 nm (resp. 2200 nm), similarly to Part I. A hundredfold concentration of sunlight can increase the efficiency by an additional 27%. Finally, the currently used 110-nm-thick layer ofperforms almost as well as optimal single- and double-layer antireflection coatings.
Electro-optic quantum coherent interfaces map the amplitude and phase of a quantum signal directly to the phase or intensity of a probe beam. At terahertz frequencies, a fundamental challenge is not only to sense such weak signals (due to a weak coupling with a probe in the near-infrared) but also to resolve them in the time domain. Cavity confinement of both light fields can increase the interaction and achieve strong coupling. Using this approach, current realizations are limited to low microwave frequencies. Alternatively, in bulk crystals, electro-optic sampling was shown to reach quantum-level sensitivity of terahertz waves. Yet, the coupling strength was extremely weak. Here, we propose an on-chip architecture that concomitantly provides subcycle temporal resolution and an extreme sensitivity to sense terahertz intracavity fields below 20 V/m. We use guided femtosecond pulses in the near-infrared and a confinement of the terahertz wave to a volume ofin combination with ultraperformant organic molecules () and accomplish a record-high single-photon electro-optic coupling rate of, 10,000 times higher than in recent reports of sensing vacuum field fluctuations in bulk media. Via homodyne detection implemented directly on chip, the interaction results into an intensity modulation of the femtosecond pulses. The single-photon cooperativity is, and the multiphoton cooperativity isat room temperature. We showdynamic range in intensity at 500 ms integration under irradiation with a weak coherent terahertz field. Similar devices could be employed in future measurements of quantum states in the terahertz at the standard quantum limit, or for entanglement of subsystems on subcycle temporal scales, such as terahertz and near-infrared quantum bits.
Wang, Yutao, Quintana, Xavier, Kim, Jiyun, Guan, Xinwei, Hu, Long, Lin, Chun-Ho, Jones, Brendon Tyler, Chen, Weijian, Wen, Xiaoming, Gao, Hanwei, and Wu, Tom.
"Phase segregation in inorganic mixed-halide perovskites: from phenomena to mechanisms". Photonics Research 8 (11). Country unknown/Code not available: Optical Society of America. https://doi.org/10.1364/PRJ.402411.https://par.nsf.gov/biblio/10201126.
@article{osti_10201126,
place = {Country unknown/Code not available},
title = {Phase segregation in inorganic mixed-halide perovskites: from phenomena to mechanisms},
url = {https://par.nsf.gov/biblio/10201126},
DOI = {10.1364/PRJ.402411},
abstractNote = {Halide perovskites, such as methylammonium lead halide perovskites (MAPbX3,X=I, Br, and Cl), are emerging as promising candidates for a wide range of optoelectronic applications, including solar cells, light-emitting diodes, and photodetectors, due to their superior optoelectronic properties. All-inorganic lead halide perovskitesCsPbX3are attracting a lot of attention because replacing the organic cations withCs+enhances the stability, and its halide-mixing derivatives offer broad bandgap tunability covering nearly the entire visible spectrum. However, there is evidence suggesting that the optical properties of mixed-halide perovskites are influenced by phase segregation under external stimuli, especially illumination, which may negatively impact the performance of optoelectronic devices. It is reported that the mixed-halide perovskites in forms of thin films and nanocrystals are segregated into a low-bandgap I-rich phase and a high-bandgap Br-rich phase. Herein, we present a critical review on the synthesis and basic properties of all-inorganic perovskites, phase-segregation phenomena, plausible mechanisms, and methods to mitigate phase segregation, providing insights on advancing mixed-halide perovskite optoelectronics with reliable performance.},
journal = {Photonics Research},
volume = {8},
number = {11},
publisher = {Optical Society of America},
author = {Wang, Yutao and Quintana, Xavier and Kim, Jiyun and Guan, Xinwei and Hu, Long and Lin, Chun-Ho and Jones, Brendon Tyler and Chen, Weijian and Wen, Xiaoming and Gao, Hanwei and Wu, Tom},
}
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