Two-dimensional Ruddlesden-Popper Perovskites Research Articles

A numerical approach to optimize the efficiency of a novel HTL-free Sr3Ti2S7 Ruddlesden-Popper perovskite solar cell

The exceptional environmental and structural stability of two-dimensional Ruddlesden-Popper perovskites has made them appealing candidates for high-performance perovskite solar cells. Besides, Ruddlesden-Popper perovskites can be synthesized using low-cost solution processing and have tunable bandgaps as compared to their conventional three-dimensional counterparts. Therefore, a Ruddlesden–Popper perovskite solar cell has been reported in this investigation and the SCAPS program has been used to theoretically study the device performance of the proposed lead-free, environmentally friendly perovskite solar cell. A novel Sr3Ti2S7 material has been utilized as the light absorber for the first time in such a theoretical study. Two different configurations, employing WS2 and C60 electron transport layers have been presented and device simulations have been performed to optimize the solar cell. The utilization of C60 as an electron transport material did not prove to be beneficial for the solar cell as it suffered from major recombination losses. It was also found that higher doping concentration of the electron transport materials could help these cells achieve improved fill factor. The diffusion length of the electrons and holes with respect to absorber defect density was also determined. Mott-Schottky analysis proved that the ITO/C60/Sr3Ti2S7/Au structure had a lower flatband potential compared to ITO/WS2/Sr3Ti2S7/Au. Additionally, from the impedance spectroscopy results, the recombination lifetime of the ITO/WS2/Sr3Ti2S7/Au configuration was found to be 46.7 μs compared to only 12.9 μs for the ITO/C60/Sr3Ti2S7/Au architecture. It was also established that if the thickness of the absorber and the bulk defect concentration were optimized the ITO/WS2/Sr3Ti2S7/Au and ITO/C60/Sr3Ti2S7/Au solar cells could achieve conversion efficiencies close to 11.0 % and 10.0 % respectively.

Water-Oil Interfacial Synthesis of Two-Dimensional Colloidal Lead-Iodide Perovskites with Enhanced Efficiency and Stability.

Two-dimensional Ruddlesden-Popper perovskites L2PbI4 (L = alkylammonium cation) (RPPs) have attracted significant attention due to their unique excitonic characteristics. However, their ultrafast reaction dynamics exacerbates the structural distortion of the inorganic framework, leading to severe deterioration in photoluminescence. Here, we propose a water-oil interfacial synthesis approach to achieve controlled growth of the RPPs nanosheets. By segregating Pb and I precursors in two immiscible solvents, the nucleation and growth of RPPs are prolonged to the minute level. L2PbI4 nanosheets terminated with various alkylammonium are synthesized, and the factors influencing the growth kinetics of RPPs nanosheets are investigated. The resulting (PEA)2PbI4 nanosheets exhibit a 3.6-time enhancement in quantum efficiency and 3.2-time improvement photostability compared to those synthesized using the classical recrystallization method. A white light-emitting diode based on (HDA)2PbI4 nanosheets is fabricated, achieving a color gamut of 119.7% of the NTSC display standards. This innovative approach offers a new method for the controlled growth of 2D RPPs with improved optical quality and stability.

Boosting MA-based two-dimensional Ruddlesden-Popper perovskite solar cells by incorporating a binary spacer

Two-dimensional Ruddlesden-Popper (2DRP) perovskite exhibits excellent stability in perovskite solar cells (PSCs) due to introducing hydrophobic long-chain organic spacers. However, the poor charge transporting property of bulky organic cation spacers limits the performance of 2DRP PSCs. Inspired by the A-site cation alloying strategy in 3D perovskites, 2DRP perovskites with a binary spacer can promote charge transporting compared to the unary spacer counterparts. Herein, the superior MA-based 2DRP perovskite films with a binary spacer, including 3-guanidinopropanoic acid (GPA) and 4-fluorophenethylamine (FPEA) are realized. These films (GPA0.85FPEA0.15)2MA4Pb5I16 show good morphology, large grain size, decreased trap state density, and preferential orientation of the as-prepared film. Accordingly, the present 2DRP-based PSC with the binary spacer achieves a remarkable efficiency of 18.37% with a VOC of 1.15 V, a JSC of 20.13 mA cm−2, and an FF of 79.23%. To our knowledge, the PCE value should be the highest for binary spacer MA-based 2DRP (n ≤ 5) PSCs to date. Importantly, owing to the hydrophobic fluorine group of FPEA and the enhanced interlayer interaction by FPEA, the unencapsulated 2DRP PSCs based on binary spacers exhibit much excellent humidity stability and thermal stability than the unary spacer counterparts.

Impact of large A-site cations on electron-vibrational interactions in 2D halide perovskites: Ab initio quantum dynamics.

Using abinitio nonadiabatic molecular dynamics, we study the effect of large A-site cations on nonradiative electron-hole recombination in two-dimensional Ruddlesden-Popper perovskites HA2APb2I7, HA = n-hexylammonium, A = methylammonium (MA), or guanidinium (GA). The steric hindrance created by large GA cations distorts and stiffens the inorganic Pb-I lattice, reduces thermal structural fluctuations, and maintains the delocalization of electrons and holes at ambient and elevated temperatures. The delocalized charges interact more strongly in the GA system than in the MA system, and the charge recombination is accelerated. In contrast, replacement of only some MA cations with GA enhances disorder and increases charge lifetime, as seen in three-dimensional perovskites. This study highlights the key influence of structural fluctuations and disorder on the properties of charge carriers in metal halide perovskites, providing guidance for tuning materials' optoelectronic performance.

Improve the Charge Carrier Transporting in Two-Dimensional Ruddlesden-Popper Perovskite Solar Cells.

Conventional 3D organic-inorganic halide perovskite materials have shown substantial potential in the field of optoelectronics, enabling the power conversation efficiency of solar cells beyond 26%. A key challenge limiting the further commercial application of 3D perovskite solar cells is their inherent instability over outer oxygen, humidity, light, and heat. By contrast, 2D Ruddlesden-Popper (2DRP) perovskites with bulky organic cations can effectively stabilize the inorganic slabs, yielding excellent environmental stability. However, the efficiencies of 2DRP perovskite solar cells are much lower than those of the 3D counterparts due to poor charge carrier transporting property of insulating bulky organic cations. Their inner structural, dielectric, optical, and excitonic properties remain to be primarily studied. In this review, the main reasons for the low efficiency of 2DRP perovskite solar cells are first analyzed. Next, a detailed description of various strategies for improving the charge carrier transporting of 2DRP perovskites is provided, such as bandgap regulation, perovskite crystal phase orientation and distribution, energy level matching, interfacial modification, etc. Finally, a summary is given, and the possible future research directions and methods to achieve high-efficiency and stable 2DRP perovskite solar cells are rationalized.

(Invited) Atomic Imaging and Device Characterization of Molecularly Thin 2D Hybrid Perovskites

2D Organic-Inorganic Hybrid perovskites (OIHPs) possess alternating layers of organic molecules and inorganic quantum wells. By tuning the interaction between organic and inorganic layers, very interesting properties can be introduced. The successful isolation of hybrid perovskite monolayers with clean and flat surfaces are particularly suitable for atomic structure characterization and optoelectronic device fabrication. In this talk, I will present recent results on the excitonic properties and atomic structure of molecularly thin OIHPs1,2. We found that a reversible shift in excitonic energies can be induced upon laser irradiation in large-sized 2D hybrid perovskite monolayers which is attributed to the reversible structural reorientation of the surface BA cations in the easily deformable lattice3. The photodetection performance of monolayer, bilayer and thicker OIHPs were compared. The internal quantum efficiency was measured to be 34% for a monolayer (BA)2(MA)3Pb4I13 and 19% for the bulk crystal. In addition, 2D heterostructures of molecularly thin OIHPs/graphene were constructed which exhibited a lower barrier than gold for carrier injection, enabling applications in field effect transistors (FETs)4. Electron tunneling occurs across the interface of organic molecular layers on 2D perovskite and graphene, while photoinduced charge transfer occurs at femtosecond timescale (~50 fs).Resolving the atomic structure of 2D hybrid perovskite is a challenging task because it is easily damaged by electron beam. Here we use scanning tunneling microscopy (STM) & Qplus AFM to directly visualize surface octahedral tilt in freshly exfoliated 2D Ruddlesden-Popper perovskites (RPPs)5. The experimentally determined octahedral tilts from n = 1 to n = 4 RPPs from STM images are found to agree very well with out-of-plane surface octahedral tilts predicted by density functional theory calculations. The surface-enhanced octahedral tilt is correlated to excitonic redshift observed in photoluminescence (PL) and promotes Rashba spin splitting for n > 1. Our studies demonstrate a protocol to investigate structure-property correlations in low dimensional 2D OIHPs, which will pave the way to better material design and device performance.References Leng, W. Fu, Y. Liu, M. Chhowalla & KP Loh* “From Bulk to Molecularly Thin Hybrid Perovskites” Nature Reviews Materials , 5, 482-500 (2020).Zhao, KP Loh, K. Leng* “Organic-inorganic hybrid perovskites and their heterostructures” Matter , 5, 4153-4169 (2022).Leng, I. Abdelwaha, I. Verzhbitskiy, M. Telychko, L. Chu, W. Fu, X. Chi, N. Guo, Z. Chen, Z. Chen, C. Zhang, Q. Xu, J. Lu, M. Chhowalla, G. Eda, KP Loh* “Molecularly thin two-dimensional hybrid perovskites with tunable optoelectronic properties due to reversible surface relaxation” Nature Materials , 17, 908-914 (2018).Leng, L. Wang, Y. Shao, I. Abdelwahab, G. Grinblat, I. Verzhbitskiy, Y. Cai, X. Chi, W. Fu, P. Song, G. Eda, S. A. Maier & KP Loh* “Electron Tunneling at the Molecularly Thin 2D Perovskite and Graphene Van der Waals Interface” Nature Communications , 11, 5483 (2020).Y Shao, W. Gao, H. Yan, R. Li, I. Abdelwahab, L. Zhuang, W. Fu, SP Lau, SF YU, Y. Cai, KP Loh, K. Leng* “Unlocking Surface Octahedral Tilt in Two-dimensional Ruddlesden-Popper Perovskites” Nature Communications , 13, 138 (2022). AcknowledgementK.L. would like to acknowledge the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. PolyU15305221 for GRF project funded in 2021/22 Exercise and Project No. PolyU25305222 for ECS project funded in 2022/23 Exercise).

Effect of surface polarization and structural deformation on the formation and stabilization of polarons in two-dimensional Ruddlesden–Popper metal halide perovskites

First-principles density-functional theory calculations were performed to reveal the effect of surface polarization and structural deformation on the formation and stabilization of the polaron in two-dimensional Ruddlesden–Popper perovskites. Our results revealed that the orientational distribution of organic cations induces surface polarization. The surface dipole moment can be well featured by the c axis distances between N and the nearest I atoms. Structural deformation and surface dipole moments result in separate real-space distributions of hole and electron polarons. Our results also reveal that the structural deformation of the [PbI6] sublattices and surface polarization are closely related to the reorientation of organic cations and can be effectively modulated by it. This reorientation significantly impacts the stabilization of polarons. Our understandings provide insight into the nature of polarons in two-dimensional Ruddlesden–Popper perovskites and general guidance for the proper selection of organic cations in two-dimensional perovskites for suitable applications in photovoltaic and optoelectronic devices.

Efficient Narrowband Photoconductivity of the Excitonic Resonance in Two-Dimensional Ruddlesden-Popper Perovskites Due to Exciton Polarons.

Filter-less, wavelength-selective photodetectors made of perovskite usually rely on the charge collection narrowing mechanism, which intrinsically limits the response times. Using the narrow excitonic peak of, e.g., two-dimensional (2D) Ruddlesden-Popper perovskites as direct absorbers to realize color-selective photodetectivity promises faster responses. However, one major challenge in realizing such devices remains the separation and charge carrier extraction of the tightly bound excitons. Here, we report on filter-less color-selective photoconductivity in 2D perovskite butylammonium lead iodide thin film devices, exhibiting a distinct resonance in the photocurrent spectrum with a full width at half-maximum of 16.5 nm that correlates to the excitonic absorption. Our devices exhibit unexpectedly efficient charge carrier separation with an external quantum efficiency of ≤8.9% at the excitonic resonance, which we trace back to the involvement of exciton polarons. Our photodetector achieves response times of 150 μs and a maximum specific detectivity of 2.5 × 1010 Jones at the excitonic peak.

Impact of light illumination on the surface structure of two-dimensional Ruddlesden–Popper perovskite in the fabrication process

Two-dimensional Ruddlesden–Popper (2DRP) perovskites are promising owing to their excellent environmental stability and competitive efficiency. During the fabrication process, 2DRP perovskites were often unintentionally exposed to light in the laboratory. However, the influence of light illumination on the surface structure of 2DRP during fabrication is unclear. Herein, the photodegradation of 2DRP perovskite (phenethylammonium lead iodide, PEA2PbI4) is comprehensively investigated using x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and photoluminescence spectroscopy. We observed that only high-energy light, including that from a blue laser, air mass 1.5G, and notably, the daily used fluorescent lamp (FL) in the laboratory, significantly degraded PEA2PbI4. However, the red laser and ultraviolet-filtered FL, which had low energies, did not cause photodegradation. From this systematic study, we can explain the discrepancies in the surface morphologies previously studied. For instance, randomly oriented nanorod or rough surface of PEA2PbI4 mostly stems from photodegradation. We observed that photodegradation occurred more strongly when the films were illuminated during annealing than when they were illuminated after all fabrication processes were completed. We suggest that this difference stems from the completeness of the structure and the photodegraded PbI2 passivation effect. Our study provides two key guidelines for the fabrication of PEA2PbI4 films. The daily-use FL in the laboratory must be avoided for high-quality samples, and dark conditions are highly recommended, at least during the annealing process.

Fine Structure Splitting of Phonon-Assisted Excitonic Transition in (PEA)2PbI4 Two-Dimensional Perovskites

Two-dimensional van der Waals materials exhibit particularly strong excitonic effects, which causes them to be an exceptionally interesting platform for the investigation of exciton physics. A notable example is the two-dimensional Ruddlesden-Popper perovskites, where quantum and dielectric confinement together with soft, polar, and low symmetry lattice create a unique background for electron and hole interaction. Here, with the use of polarization-resolved optical spectroscopy, we have demonstrated that the simultaneous presence of tightly bound excitons, together with strong exciton-phonon coupling, allows for observing the exciton fine structure splitting of the phonon-assisted transitions of two-dimensional perovskite (PEA)2PbI4, where PEA stands for phenylethylammonium. We demonstrate that the phonon-assisted sidebands characteristic for (PEA)2PbI4 are split and linearly polarized, mimicking the characteristics of the corresponding zero-phonon lines. Interestingly, the splitting of differently polarized phonon-assisted transitions can be different from that of the zero-phonon lines. We attribute this effect to the selective coupling of linearly polarized exciton states to non-degenerate phonon modes of different symmetries resulting from the low symmetry of (PEA)2PbI4 lattice.

Regulating Radial Morphology in Hot-Casting Two-Dimensional Ruddlesden–Popper Perovskite Film Growth for High-Efficient Photovoltaics

Two-dimensional (2D) perovskites have attracted significant attention in recent years due to their promising light harvesting and emissive properties. However, the realization of 2D perovskite crystallization with sufficient coverage and reliable reproducibility remains difficult. In this study, controlling the solvent volatilization to achieve high-quality crystallization with full coverage and lateral homogeneity of 2D Ruddlesden–Popper phase perovskite was effectively achieved. It is found that variations in the solvent evaporation rate give rise to lateral film coverage gradients with the degree of grain fusion during the process of hot-casting. As a result, the obtained photovoltaic efficiency varies due to the growth inhomogeneity across hot-casting thin films from center to edge. By adjusting the temperature of the casting perovskite precursor, film inhomogeneity and device performance variation can be alleviated. Regulating radial morphology across hot-casting thin films will enable coating techniques amenable to the solution process for robust reproducibility.

Structural, vibrational, photoelectrochemical, and optical properties of two-dimensional Ruddlesden-Popper perovskite BA2PbI4 crystals.

Two-dimensional organic-inorganic hybrid Ruddlesden-Popper perovskites have attracted a lot of attention due to their unique photochemical properties and enhanced stability towards photoluminescence devices. Compared with three-dimensional materials, two-dimensional perovskites show great potential for photoelectric applications due to their tunable band gap, great excitation binding energy, and large crystal anisotropy. Although the synthesis and optical properties of BA2PbI4 crystals have been extensively studied, the role of their microstructure in photoelectric applications, their electronic structure, and their electron-phonon interaction are still poorly understood. In this paper, based on the preparation of BA2PbI4 crystals, the electronic structure, phonon dispersion, and vibrational properties of BA2PbI4 crystals were revealed in detail with the help of density functional theory. The BA2PbI4 stability diagram of formation enthalpy was calculated. The crystal structure of the BA2PbI4 crystals was characterized and calculated with the aid of Rietveld refinement. A contactless fixed-point lighting device was designed based on the principle of an electromagnetic induction coil, and the points with different thicknesses of BA2PbI4 crystal were tested. It is proved that the excitation peak of the bulk is 564 nm, and the surface luminescence peak is 520 nm. Phonon dispersion curves and the total and partial phonon densities of states have been calculated for the BA2PbI4 crystals. The calculated results are in good agreement with the experimental Fourier infrared spectra. Besides the basic characterization of the BA2PbI4 crystals, the photoelectrochemical properties of the materials were also studied, which further proves the excellent photoelectric properties of the BA2PbI4 crystals and the broad application prospect.

Recent progress of two-dimensional Ruddlesden–Popper perovskites in solar cells

This review mainly focuses on the research progress, performance improvement methods, surface passivation application, and limitations of 2D RP PSCs with several typical spacer cations, their challenges and outlook also are briefly described.

Modifying the optical emission of two-dimensional Ruddlesden-Popper perovskites by laser irradiation

Two-dimensional (2D) organic–inorganic hybrid perovskites, especially Ruddlesden-Popper (RP) perovskites, have attracted great interest in recent years due to their potential applications in the fields of optoelectronics and photovoltaics. In this work, the effects of laser irradiation on the optical emission of a PEA2MA2Pb3I10 thin film (PTF) were systematically investigated by using 488-nm continuous wave laser light and 400-nm femtosecond laser light as the excitation sources. It was found that the photoluminescence (PL) intensity of a PTF increases rapidly with irradiation time and becomes saturated after some time, which is ascribed to the passivation of the defects near the surface of the PTF through the interaction with oxygen. A large redshift of the PL wavelength from ∼ 625 to ∼ 750 nm was realized by simply increasing the laser power. It was suggested that the decomposition of PEA2MA2Pb3I10 into MAPbI3 is responsible for this behavior. The excitation efficiency was improved while the threshold laser power for the decomposition was lowered by constructing a particle-on-film system with a silica microsphere. In this way, the blueshift of the PL wavelength from ∼ 750 to ∼ 520 nm, which is attributed to the further decomposition of MAPbI3 into PbI2, was achieved. Our findings provide a simple and effective way for modifying the optical emission of 2D perovskites and pave the way for realizing photonic devices based on 2D perovskites.

Charge Transfer Dynamics of Two-Dimensional Ruddlesden Popper Perovskite in the Presence of Short-Chain Aromatic Thiol Ligands

Two-dimensional (2D) Ruddlesden Popper perovskites (RPP) are highly important in light-harvesting and photovoltaic applications. The formation of a repetitive quantum well structure by alternating organic and inorganic layers leads to dielectric confinement of charges, which essentially inhibits the effective charge transport. In this work, we have investigated the impact of bifunctional short-chain aromatic ligands, namely, 4-aminothiophenol (ATP) and 4-nitrothiophenol (NTP), on the charge transfer dynamics of 2D RPP. The electron transfer from 2D RPP to NTP and the hole transfer from 2D RPP to ATP are evident from ultrafast transient absorption spectroscopy, depending on the nature of ligands, and the electron transfer and hole transfer occur in 900 fs and 1.9 ps, respectively. Our results provide insights for understanding the charge transfer dynamics in the presence of short-chain aromatic thiol ligands with 2D RPP, which will facilitate the performance of next-generation optoelectronic devices.

Two-Photon Lasing from Two-Dimensional Homologous Ruddlesden-Popper Perovskite with Giant Nonlinear Absorption and Natural Microcavities.

Two-dimensional Ruddlesden-Popper perovskites (RPPs) with multiple quantum well-like structures, strong excitonic quantum confinement, and high stability are promising optical gain media. However, the lasing from such material with a small number of inorganic well layers is difficult to achieve. Herein, we demonstrate the low-threshold upconversion lasing from the homologous RPP (PEA)2(MA)n-1PbnI3n+1 (n = 2 and 3) microflakes with wavelength varies from 598 to 637 nm under 800 nm laser excitation at low temperature (≤153 K). Using the micro Z-scan technique, we discovered that the RPP flakes have a giant two-photon absorption coefficient β as high as 3.6 × 103 cm GW-1, resulting in the effective upconversion transition under two-photon excitation. Furthermore, the self-formation of Fabry-Pérot microcavities provides the support for lasing emission from the n ≥ 2 RPP flakes. Calculation results and microscopic transient absorption measurements reveal that low-threshold lasing is due to the high differential gain coefficient and the suppressed nonradiative Auger recombination rate inside the quantum confinement structures. These properties enable RPPs as potential gain media for developing upconversion microcavity lasers.

Point Defects in Two-Dimensional Ruddlesden-Popper Perovskites Explored with Ab Initio Calculations.

Two-dimensional Ruddlesden-Popper (RP) halide perovskites stand out as excellent layered materials with favorable optoelectronic properties for efficient light-emitting, spintronic, and other spin-related applications. However, properties often determined by defects are not well understood in these perovskite systems. This work investigates the ground state electronic structure of commonly formed defects in a typical RP perovskite structure by density functional theory. Our study reveals that these 2D perovskites generally retain their defect tolerance with limited perturbation of the electronic structure in the case of neutral-type point defects. In contrast, donor/acceptor defects induce deep midgap states, potentially causing harm to the material's electronic performance. To retain positive intrinsic properties, the halide vacancies and interstitial defects should be avoided. The observed strong electron localization results in trap states and consequently leads to reduced device performance. This understanding can guide experimental efforts that aim for improved 2D halide perovskite-based device performance.

Internal Built-In Electric Fields at Organic-Inorganic Interfaces of Two-Dimensional Ruddlesden-Popper Perovskite Single Crystals.

Two-dimensional (2D) organic-inorganic hybrid Ruddlesden-Popper perovskites (OIRPPs), which consist of naturally formed "multiple quantum well (MQW)-like" structure, have received considerable interest in optoelectronic applications, owing to their outstanding optical properties and tailorable functionalities. While the quantum-confined electrons and holes at an MQW structure are under an applied electric field, the tilt of the energy bands may cause a significant influence on their optical properties. This work demonstrates the presence of internal built-in electric fields (BIEFs) at the as-synthesized 2D OIRPP single crystals. Spontaneous Franz-Keldysh oscillations, which usually act as the fingerprint to account for the presence of BIEFs in the MQW-like structures, are observed at 2D OIRPPs by the highly sensitive differential technique of modulated thermoreflectance spectroscopy. The strength of BIEFs at 2D OIRPP single crystals reduces with increased n values due to the increased width of the quantum well. The origin of the presence of BIEFs at 2D OIRPPs is further unveiled by atomically resolved scanning tunneling microscopy on their electronic band structures at organic-inorganic interfaces. Unlike the conventional III-V MQW semiconductors with the BIEFs, which are dominated by the spatial concentration gradients at heterointerfaces, the presence of BIEFs at the 2D OIRPP single crystals is attributed to the molecular dipoles within organic spacers pointing to the organic-inorganic interfaces. The discovery of internal BIEFs at the 2D OIRPPs may provide deep insight into understanding the fundamental optical properties for the future design of large-area and low-cost perovskite optoelectronic devices.

Polariton Dynamics in Two-Dimensional Ruddlesden-Popper Perovskites Strongly Coupled with Plasmonic Lattices.

Strong coupling between light and matter can produce hybrid eigenstates known as exciton-polaritons. Although polariton dynamics are important photophysical properties, the relaxation pathways of polaritons in different coupling regimes have seen limited attention. This paper reports the dynamics of hybridized states from 2D Ruddlesden-Popper perovskites coupled to plasmonic nanoparticle lattices. The open cavity architecture of Al lattices enables the coupling strength to be modulated by varying either the lead halide perovskite film thickness or the superstrate refractive index. Both experiments and finite-difference time-domain simulations of the optical dispersion diagrams showed avoided crossings that are a signature of strong coupling. Our analytical model also elucidated the correlation between the exciton/plasmon mixing ratio and polariton coupling strength. Using fs-transient absorption spectroscopy, we found that both the upper and lower polaritons have shorter lifetimes than the excitons and that polaritons can show faster excited-state dynamics when they have access to additional energy transfer channels.

Photoluminescence Enhancement in Thin Two-Dimensional Ruddlesden–Popper Perovskites by Spiro-OMeTAD

Photoluminescence Enhancement in Thin Two-Dimensional Ruddlesden–Popper Perovskites by Spiro-OMeTAD