arXiv subjects

Juan-Pablo Correa-Baena

Publications and source records attributed to Juan-Pablo Correa-Baena.

13 recordsLinked to original sources

arXiv2025

Resolving exciton and polariton multi-particle correlations in an optical microcavity in the strong coupling regime

Multi-particle correlations of exciton-polaritons and reservoir-excitons in the strong light-matter coupling regime dictate the quantum dynamics of optical microcavities. In this letter, we examine the many-body exciton-polariton dynamics in a Fabry-Pérot microcavity of a two-dimensional metal-halide semiconductor over timescales involving polariton ($\ll 1$\,ps) and exciton ($\gg 1$\,ps) scattering. We find enhanced exciton nonlinear dynamics in the microcavity versus the bare semiconductor, concomitant with ultrafast polariton scattering dynamics. We measure, by means of coherent spectroscopy, the coupling between exciton-polaritons, bright excitons, and reservoir-excitons that highlight the complex scattering landscape that fundamentally drives polariton condensation.

cond-mat.mtrl-sci↗

arXiv2025

Machine Learning Reveals Composition Dependent Thermal Stability in Halide Perovskites

Halide perovskites exhibit unpredictable properties in response to environmental stressors, due to several composition-dependent degradation mechanisms. In this work, we apply data visualization and machine learning (ML) techniques to reveal unexpected correlations between composition, temperature, and material properties while using high throughput, in situ environmental photoluminescence (PL) experiments. Correlation heatmaps show the strong influence of Cs content on film degradation, and dimensionality reduction visualization methods uncover clear composition-based data clusters. An extreme gradient boosting algorithm (XGBoost) effectively forecasts PL features for ten perovskite films with both composition-agnostic (>85% accuracy) and composition-dependent (>75% accuracy) model approaches, while elucidating the relative feature importance of composition (up to 99%). This model validates a previously unseen anti-correlation between Cs content and material thermal stability. Our ML-based framework can be expanded to any perovskite family, significantly reducing the analysis time currently employed to identify stable options for photovoltaics.

cond-mat.mtrl-sci↗

arXiv2025

Spectroscopic signatures of biexcitons: A case study in Ruddlesden-Popper lead-halides

Exciton-exciton interactions are fundamental to the light-emitting properties of semiconductors, influencing applications from lasers to quantum light sources. In this study, we investigate the spectroscopic signatures and binding energy of biexcitons in a metal halide two-dimensional Ruddlesden-Popper structure, which is known for hosting distinct excitonic resonances with unique lattice coupling. Using three spectroscopic techniques - photoluminescence (PL) and two variations of two-dimensional electronic spectroscopy (2DES) - we map coherent one-quantum and two-quantum correlations to gain deeper insight into the biexciton characteristics. While PL spectroscopy is hindered by spectral broadening and reabsorption, 2DES provides a more accurate characterization, revealing multiple biexciton states and uncovering a mixed biexciton species arising from exciton cross-coupling. These findings highlight the importance of advanced spectroscopic approaches in accurately determining biexciton binding energies and offer new perspectives on many-body interactions in exciton-polarons within layered perovskites.

cond-mat.mtrl-sci↗

arXiv2025

Fine-Tuning Exciton Polaron Characteristics via Lattice Engineering in 2D Hybrid Perovskites

The layered structure of 2D metal halide perovskites (MHPs) consisting of an ionic metal halide octahedral layer electronically separated by an organic cation, exhibits strong coupling between high-binding-energy excitons and low-energy lattice phonons. Photoexcitations in these systems are believed to be exciton polarons, Coulombically bound electron-hole pairs dressed by lattice vibrations. Understanding and controlling the structural and chemical factors that govern this interaction is crucial for optimizing exciton recombination, transport, and many-body interactions. Our study examines the role of the organic cation in a prototypical 2D-MHP system, phenylethylammonium lead iodide, (PEA)2PbI4, and its halogenated derivatives, (F/Cl-PEA)2PbI4. These substitutions allow us to probe polaronic effects while maintaining the average lattice and electronic structure. Using resonant impulsive stimulated Raman scattering (RISRS), we analyze the metal-halide sub-lattice motion coupled to excitons. We apply formalism based on a perturbative expansion of the nonlinear response function on the experimental data to estimate the Huang-Rhys parameter, $S=1/2 Δ^2$, to quantify the lattice displacement ($Δ$) due to exciton-phonon coupling. A direct correlation emerges between lattice displacement and octahedral distortion, with F-PEA exhibiting the largest shift and Cl-PEA exhibiting the least, significantly influencing the fine structure features in absorption. Additionally, 2D electronic spectroscopy reveals that F-PEA, with the strongest polaronic coupling, exhibits the least thermal dephasing, supporting the polaronic protection hypothesis. Our findings suggest that systematic organic cation substitution serves as a tunable control for the fine structure in 2D-MHPs, and offers a pathway to mitigate many-body scattering effects by tailoring the polaronic coupling.

cond-mat.mtrl-sci↗

arXiv2024

Diamine Surface Passivation and Post-Annealing Enhance Performance of Silicon-Perovskite Tandem Solar Cells

We show that the use of 1,3-diaminopropane (DAP) as a chemical modifier at the perovskite/electron-transport layer (ETL) interface enhances the power conversion efficiency (PCE) of 1.7 eV bandgap FACs mixed-halide perovskite single-junction cells, primarily by boosting the open-circuit voltage (VOC) from 1.06 V to 1.15 V. Adding a post-processing annealing step after C60 evaporation, further improves the fill factor (FF) by 20% from the control to the DAP + post-annealing devices. Using hyperspectral photoluminescence microscopy, we demonstrate that annealing helps improve compositional homogeneity at the top and bottom interfaces of the solar cell, which prevents detrimental bandgap pinning in the devices and improves C60 adhesion. Using time-of-flight secondary ion mass spectrometry, we show that DAP reacts with formamidinium present near the surface of the perovskite lattice to form a larger molecular cation, 1,4,5,6-tetrahydropyrimidinium (THP) that remains at the interface. Combining the use of DAP and the annealing of C60 interface, we fabricate Si-perovskite tandems with PCE of 25.29%, compared to 23.26% for control devices. Our study underscores the critical role of chemical reactivity and thermal post-processing of the C60/Lewis-base passivator interface in minimizing device losses and advancing solar-cell performance of wide-bandgap mixed-cation mixed-halide perovskite for tandem application.

cond-mat.mtrl-sci↗

arXiv2024

Super-Bandgap Electroluminescence from Cesium Lead Bromide

Halide perovskites is a new class of semiconductors with exceptional optoelectronic properties. Among many advantages offered by halide perovskites, the bandgap energy can be tuned in a much broader range than what was possible in conventional semiconductors. This was commonly achieved in previous research by mixing different species of halides into solid solutions. The tuned bandgap using this method, however, often underwent an energy shift under optical or electrical stimuli due to halide segregation. In this work, we discovered an alternative approach to achieve super-bandgap electroluminescence from CsPbBr3. The peak energy of the light emission can be 0.7 eV higher than the reported bandgap energy. Evidence pointed to the radiative recombination at the perovskite-PEDOT:PSS interface being responsible for the unexpected blueshift of electroluminescence. We speculated that perovskite nanocrystals were formed therein and produced higher-energy photons due to quantum confinement. The results suggested an alternative strategy to manipulate and stabilize the color of electroluminescence and achieve particularly blue emission in perovskite-based LEDs.

physics.app-ph↗

arXiv2023

Resolving nonlinear recombination dynamics in semiconductors via ultrafast excitation correlation spectroscopy: Photoluminescence versus photocurrent detection

We explore the application of excitation correlation spectroscopy to detect nonlinear photophysical dynamics in two distinct semiconductor classes through time-integrated photoluminescence and photocurrent measurements. In this experiment, two variably delayed femtosecond pulses excite the semiconductor, and the time-integrated photoluminescence or photocurrent component arising from the nonlinear dynamics of the populations induced by each pulse is measured as a function of inter-pulse delay by phase-sensitive detection with a lock-in amplifier. We focus on two limiting materials systems with contrasting optical properties: a prototypical lead-halide perovskite (LHP) solar cell, in which primary photoexcitations are charge photocarriers, and a single-component organic-semiconductor diode, which features Frenkel excitons as primary photoexcitations. The photoexcitation dynamics perceived by the two detection schemes in these contrasting systems are distinct. Nonlinear-dynamic contributions in the photoluminescence detection scheme arise from contributions to radiative recombination in both materials systems, while photocurrent arises directly in the LHP but indirectly following exciton dissociation in the organic system. Consequently, the basic photophysics of the two systems are reflected differently when comparing measurements with the two detection schemes.

cond-mat.mtrl-sci↗

arXiv2019

Perovskite PV-powered RFID: enabling low-cost self-powered IoT sensors

Photovoltaic (PV) cells have the potential to serve as on-board power sources for low-power IoT devices. Here, we explore the use of perovskite solar cells to power Radio Frequency (RF) backscatter-based IoT devices with a few μW power demand. Perovskites are suitable for low-cost, high-performance, low-temperature processing, and flexible light energy harvesting that hold the possibility to significantly extend the range and lifetime of current backscatter techniques such as Radio Frequency Identification (RFID). For these reasons, perovskite solar cells are prominent candidates for future low-power wireless applications. We report on realizing a functional perovskite-powered wireless temperature sensor with 4 m communication range. We use a 10.1% efficient perovskite PV module generating an output voltage of 4.3 V with an active area of 1.06 cm2 under 1 sun illumination, with AM 1.5G spectrum, to power a commercial off-the-shelf RFID IC, requiring 10 - 45 μW of power. Having an on-board energy harvester provides extra-energy to boost the range of the sensor (5x) in addition to providing energy to carry out high-volume sensor measurements (hundreds of measurements per min). Our evaluation of the prototype suggests that perovskite photovoltaic cells are able to meet the energy needs to enable fully autonomous low-power RF backscatter applications of the future. We conclude with an outlook into a range of applications that we envision to leverage the synergies offered by combining perovskite photovoltaics and RFID.

eess.SP↗

arXiv2019

Self-powered sensors enabled by wide-bandgap perovskite indoor photovoltaic cells

We present a new approach to ubiquitous sensing for indoor applications, using high-efficiency and low-cost indoor perovksite photovoltaic cells as external power sources for backscatter sensors. We demonstrate wide-bandgap perovskite photovoltaic cells for indoor light energy harvesting with the 1.63eV and 1.84 eV devices demonstrate efficiencies of 21% and 18.5% respectively under indoor compact fluorescent lighting, with a champion open-circuit voltage of 0.95 V in a 1.84 eV cell under a light intensity of 0.16 mW/cm2. Subsequently, we demonstrate a wireless temperature sensor self-powered by a perovskite indoor light-harvesting module. We connect three perovskite photovoltaic cells in series to create a module that produces 14.5 uW output power under 0.16 mW/cm2 of compact fluorescent illumination with an efficiency of 13.2%. We use this module as an external power source for a battery-assisted RFID temperature sensor and demonstrate a read range by of 5.1 meters while maintaining very high frequency measurements every 1.24 seconds. Our combined indoor perovskite photovoltaic modules and backscatter radio-frequency sensors are further discussed as a route to ubiquitous sensing in buildings given their potential to be manufactured in an integrated manner at very low-cost, their lack of a need for battery replacement and the high frequency data collection possible.

physics.app-ph↗

arXiv2019

Triplet-sensitization by lead halide perovskite thin films for near-infrared-to-visible upconversion

Lead halide-based perovskite thin films have attracted great attention due to the explosive increase in perovskite solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials in solar cells are also beneficial in other light-harvesting applications and make them prime candidates as triplet sensitizers in upconversion via triplet-triplet annihilation in rubrene. In this contribution, we take advantage of long carrier lifetimes and carrier diffusion lengths in perovskite thin films, their high absorption cross sections throughout the visible spectrum, as well as the strong spin-orbit coupling owing to the abundance of heavy atoms to sensitize the upconverter rubrene. Employing bulk perovskite thin films as the absorber layer and spin-mixer in inorganic/organic heterojunction upconversion devices allows us to forego the additional tunneling barrier owing from the passivating ligands required for colloidal sensitizers. Our bilayer device exhibits an upconversion efficiency in excess of 3% under 785 nm illumination.

physics.app-ph↗

arXiv2019

Trap states impact photon upconversion in rubrene sensitized by lead halide perovskite thin films

The same optical and electronic properties that make perovskite thin films ideal absorber materials in photovoltaic applications are also beneficial in photon upconversion devices. In this contribution, we investigate the rubrene-triplet sensitization by perovskite thin films based on methylammonium formamidinium lead triiodide (MAFA). To elucidate the role of trap states which affect the free carrier lifetimes, we fabricate MAFA perovskite thin films with three different thicknesses. By measuring the change in the photoluminescence properties under different excitation fluences, we find that the prevalent recombination mechanism shifts from monomolecular for thinner films to bimolecular recombination for thicker MAFA films, indicating a reduction in shallow trap-assisted recombination. The addition of rubrene shows a passivating effect on the MAFA surface, but adds an additional quenching pathway due to charge transfer to the triplet state of rubrene. We observe that the threshold for efficient triplet-triplet annihilation shifts to lower incident powers with increasing MAFA thickness, which suggests that the charge transfer to the triplet state competes with non-radiative trap filling. Hence, injection of free electrons and holes into the upconverting organic semiconductor can provide a new avenue for sensitization of rubrene, and may allow us to move away from the necessity of efficient excitonic singlet-to-triplet converters.

physics.app-ph↗

arXiv2018

Accelerating Photovoltaic Materials Development via High-Throughput Experiments and Machine-Learning-Assisted Diagnosis

Accelerating the experimental cycle for new materials development is vital for addressing the grand energy challenges of the 21st century. We fabricate and characterize 75 unique halide perovskite-inspired solution-based thin-film materials within a two-month period, with 87% exhibiting band gaps between 1.2 eV and 2.4 eV that are of interest for energy-harvesting applications. This increased throughput is enabled by streamlining experimental workflows, developing a set of precursors amenable to high-throughput synthesis, and developing machine-learning assisted diagnosis. We utilize a deep neural network to classify compounds based on experimental X-ray diffraction data into 0D, 2D, and 3D structures more than 10 times faster than human analysis and with 90% accuracy. We validate our methods using lead-halide perovskites and extend the application to novel lead-free compositions. The wider synthesis window and faster cycle of learning enables three noteworthy scientific findings: (1) we realize four inorganic layered perovskites, A3B2Br9 (A = Cs, Rb; B = Bi, Sb) in thin-film form via one-step liquid deposition; (2) we report a multi-site lead-free alloy series that was not previously described in literature, Cs3(Bi1-xSbx)2(I1-xBrx)9; and (3) we reveal the effect on bandgap (reduction to <2 eV) and structure upon simultaneous alloying on the B-site and X-site of Cs3Bi2I9 with Sb and Br. This study demonstrates that combining an accelerated experimental cycle of learning and machine-learning based diagnosis represents an important step toward realizing fully-automated laboratories for materials discovery and development.

physics.app-ph↗

arXiv2018

Homogenization of Halide Distribution and Carrier Dynamics in Alloyed Organic-Inorganic Perovskites

Perovskite solar cells have shown remarkable efficiencies beyond 22%, through organic and inorganic cation alloying. However, the role of alkali-metal cations is not well-understood. By using synchrotron-based nano-X-ray fluorescence and complementary measurements, we show that when adding RbI and/or CsI the halide distribution becomes homogenous. This homogenization translates into long-lived charge carrier decays, spatially homogenous carrier dynamics visualized by ultrafast microscopy, as well as improved photovoltaic device performance. We find that Rb and K phase-segregate in highly concentrated aggregates. Synchrotron-based X-ray-beam-induced current and electron-beam-induced current of solar cells show that Rb clusters do not contribute to the current and are recombination active. Our findings bring light to the beneficial effects of alkali metal halides in perovskites, and point at areas of weakness in the elemental composition of these complex perovskites, paving the way to improved performance in this rapidly growing family of materials for solar cell applications.

cond-mat.mtrl-sci↗