Nonlinear terahertz control of the lead halide perovskite lattice

Lead halide perovskites (LHPs) have emerged as an excellent class of semiconductors for next-generation solar cells and optoelectronic devices. Tailoring physical properties by fine-tuning the lattice structures has been explored in these materials by chemical composition or morphology. Nevertheless, its dynamic counterpart, phonon-driven ultrafast material control, as contemporarily harnessed for oxide perovskites, has not yet been established. Here, we use intense THz electric fields to obtain direct lattice control via nonlinear excitation of coherent octahedral twist modes in hybrid CH3NH3PbBr3 and all-inorganic CsPbBr3 perovskites. These Raman-active phonons at 0.9 to 1.3 THz are found to govern the ultrafast THz-induced Kerr effect in the low-temperature orthorhombic phase and thus dominate the phonon-modulated polarizability with potential implications for dynamic charge carrier screening beyond the Fröhlich polaron. Our work opens the door to selective control of LHP’s vibrational degrees of freedom governing phase transitions and dynamic disorder

Dynamiques ultrarapides dans les pérovskites hybrides

Hybrid lead halide perovskites (ABX3) are an intriguing class of semiconductors with excellent optoelectronic properties and promising for photovoltaic applications. A fundamental understanding of the ultrafast dynamics in these materials is required. This work deals with two main topics: (1) The study of electron relaxation in the conduction band using time-resolved photoemission (2PPE) and angle-resolved photoemission (tr-ARPES). Here, the influence of the orientation of A-site cations and crystallographic structure on charge screening have been studied, explaining the high tolerance to electron trapping on the surface in MAPbI3 crystals. (2) Understanding the dynamic role of phonons and their influence on electrons using the THz-induced Kerr effect. We obtained coherent control over a Raman-active Pb-Br sublattice mode, which was found to dominate the ultrafast lattice polarizability in both single and complex A-site cation perovskites. This finding highlights the potential of the inorganic lattice for dynamic carrier screening and the related mechanism of charge carrier protection.Les pérovskites hybrides aux halogénures de plomb (ABX3) sont une classe de semi-conducteurs présentant d’excellentes propriétés optoélectroniques et particulièrement prometteuses pour les applications photovoltaïques. Une compréhension fondamentale des dynamiques ultrarapides de ces matériaux est nécessaire. Ces travaux traitent deux thématiques principales : (1) L’étude de la relaxation des électrons dans la bande de conduction à l’aide de la photoémission résolue en temps et en angle. Cette technique a permis d’étudier l’influence de l’orientation des cations A et de la structure cristallographique sur l’écrantage des charges et ainsi d’expliquer la grande tolérance au piégeage des électrons sur la surface des cristaux de MAPbI3. (2) Comprendre le rôle des phonons et leur influence sur les électrons à l’aide de l’effet Kerr excité au THz. Le mode de phonon Raman le plus polarisable lié au sous-réseau Pb-Br a été dévoilé dans les pérovskites à cation A unique et complexe. Cette découverte met en évidence le rôle du réseau inorganique le mécanisme d’écrantage des porteurs de charges

Dynamiques ultrarapides dans les pérovskites hybrides

Hybrid lead halide perovskites (ABX3) are an intriguing class of semiconductors with excellent optoelectronic properties and promising for photovoltaic applications. A fundamental understanding of the ultrafast dynamics in these materials is required. This work deals with two main topics: (1) The study of electron relaxation in the conduction band using time-resolved photoemission (2PPE) and angle-resolved photoemission (tr-ARPES). Here, the influence of the orientation of A-site cations and crystallographic structure on charge screening have been studied, explaining the high tolerance to electron trapping on the surface in MAPbI3 crystals. (2) Understanding the dynamic role of phonons and their influence on electrons using the THz-induced Kerr effect. We obtained coherent control over a Raman-active Pb-Br sublattice mode, which was found to dominate the ultrafast lattice polarizability in both single and complex A-site cation perovskites. This finding highlights the potential of the inorganic lattice for dynamic carrier screening and the related mechanism of charge carrier protection.Les pérovskites hybrides aux halogénures de plomb (ABX3) sont une classe de semi-conducteurs présentant d’excellentes propriétés optoélectroniques et particulièrement prometteuses pour les applications photovoltaïques. Une compréhension fondamentale des dynamiques ultrarapides de ces matériaux est nécessaire. Ces travaux traitent deux thématiques principales : (1) L’étude de la relaxation des électrons dans la bande de conduction à l’aide de la photoémission résolue en temps et en angle. Cette technique a permis d’étudier l’influence de l’orientation des cations A et de la structure cristallographique sur l’écrantage des charges et ainsi d’expliquer la grande tolérance au piégeage des électrons sur la surface des cristaux de MAPbI3. (2) Comprendre le rôle des phonons et leur influence sur les électrons à l’aide de l’effet Kerr excité au THz. Le mode de phonon Raman le plus polarisable lié au sous-réseau Pb-Br a été dévoilé dans les pérovskites à cation A unique et complexe. Cette découverte met en évidence le rôle du réseau inorganique le mécanisme d’écrantage des porteurs de charges

Dynamiques ultrarapides dans les pérovskites hybrides

Les pérovskites hybrides aux halogénures de plomb (ABX3) sont une classe de semi-conducteurs présentant d’excellentes propriétés optoélectroniques et particulièrement prometteuses pour les applications photovoltaïques. Une compréhension fondamentale des dynamiques ultrarapides de ces matériaux est nécessaire. Ces travaux traitent deux thématiques principales : (1) L’étude de la relaxation des électrons dans la bande de conduction à l’aide de la photoémission résolue en temps et en angle. Cette technique a permis d’étudier l’influence de l’orientation des cations A et de la structure cristallographique sur l’écrantage des charges et ainsi d’expliquer la grande tolérance au piégeage des électrons sur la surface des cristaux de MAPbI3. (2) Comprendre le rôle des phonons et leur influence sur les électrons à l’aide de l’effet Kerr excité au THz. Le mode de phonon Raman le plus polarisable lié au sous-réseau Pb-Br a été dévoilé dans les pérovskites à cation A unique et complexe. Cette découverte met en évidence le rôle du réseau inorganique le mécanisme d’écrantage des porteurs de charges.Hybrid lead halide perovskites (ABX3) are an intriguing class of semiconductors with excellent optoelectronic properties and promising for photovoltaic applications. A fundamental understanding of the ultrafast dynamics in these materials is required. This work deals with two main topics: (1) The study of electron relaxation in the conduction band using time-resolved photoemission (2PPE) and angle-resolved photoemission (tr-ARPES). Here, the influence of the orientation of A-site cations and crystallographic structure on charge screening have been studied, explaining the high tolerance to electron trapping on the surface in MAPbI3 crystals. (2) Understanding the dynamic role of phonons and their influence on electrons using the THz-induced Kerr effect. We obtained coherent control over a Raman-active Pb-Br sublattice mode, which was found to dominate the ultrafast lattice polarizability in both single and complex A-site cation perovskites. This finding highlights the potential of the inorganic lattice for dynamic carrier screening and the related mechanism of charge carrier protection

Dynamiques ultrarapides dans les pérovskites hybrides

Hybrid lead halide perovskites (ABX3) are an intriguing class of semiconductors with excellent optoelectronic properties and promising for photovoltaic applications. A fundamental understanding of the ultrafast dynamics in these materials is required. This work deals with two main topics: (1) The study of electron relaxation in the conduction band using time-resolved photoemission (2PPE) and angle-resolved photoemission (tr-ARPES). Here, the influence of the orientation of A-site cations and crystallographic structure on charge screening have been studied, explaining the high tolerance to electron trapping on the surface in MAPbI3 crystals. (2) Understanding the dynamic role of phonons and their influence on electrons using the THz-induced Kerr effect. We obtained coherent control over a Raman-active Pb-Br sublattice mode, which was found to dominate the ultrafast lattice polarizability in both single and complex A-site cation perovskites. This finding highlights the potential of the inorganic lattice for dynamic carrier screening and the related mechanism of charge carrier protection.Les pérovskites hybrides aux halogénures de plomb (ABX3) sont une classe de semi-conducteurs présentant d’excellentes propriétés optoélectroniques et particulièrement prometteuses pour les applications photovoltaïques. Une compréhension fondamentale des dynamiques ultrarapides de ces matériaux est nécessaire. Ces travaux traitent deux thématiques principales : (1) L’étude de la relaxation des électrons dans la bande de conduction à l’aide de la photoémission résolue en temps et en angle. Cette technique a permis d’étudier l’influence de l’orientation des cations A et de la structure cristallographique sur l’écrantage des charges et ainsi d’expliquer la grande tolérance au piégeage des électrons sur la surface des cristaux de MAPbI3. (2) Comprendre le rôle des phonons et leur influence sur les électrons à l’aide de l’effet Kerr excité au THz. Le mode de phonon Raman le plus polarisable lié au sous-réseau Pb-Br a été dévoilé dans les pérovskites à cation A unique et complexe. Cette découverte met en évidence le rôle du réseau inorganique le mécanisme d’écrantage des porteurs de charges

Nonlinear terahertz control of the lead halide perovskite lattice

Lead halide perovskites (LHPs) have emerged as an excellent class of semiconductors for next-generation solar cells and optoelectronic devices. Tailoring physical properties by fine-tuning the lattice structures has been explored in these materials by chemical composition or morphology. Nevertheless, its dynamic counterpart, phonon-driven ultrafast material control, as contemporarily harnessed for oxide perovskites, has not yet been established. Here, we use intense THz electric fields to obtain direct lattice control via nonlinear excitation of coherent octahedral twist modes in hybrid CH3NH3PbBr3 and all-inorganic CsPbBr3 perovskites. These Raman-active phonons at 0.9 to 1.3 THz are found to govern the ultrafast THz-induced Kerr effect in the lowtemperature orthorhombic phase and thus dominate the phonon-modulated polarizability with potential implications for dynamic charge carrier screening beyond the Frohlich polaron. Our work opens the door to selective control of LHP's vibrational degrees of freedom governing phase transitions and dynamic disorder.ISSN:2375-254

Electron Dynamics in Hybrid Perovskites Reveal the Role of Organic Cations on the Screening of Local Charges

International audienceThe large tolerance of hybrid perovksites to the trapping of electrons by defects is a key asset in photovoltaic applications. Here, the ionic surface terminations of CH3NH3PbI3 are employed as a testbed to study the effect of electrostatic fields on the dynamics of excited carriers. We characterize the transition across the tetragonal to orthorhombic phase. The observed type II band offset and drift of the excited electrons highlight the important role that organic cations have on the screening of local electrostatic fields. When the orientation of organic cations is frozen in the orthorhombic phase, the positively charged termination induces a massive accumulation of excited electrons at the surface of the sample. Conversely, no electron accumulation is observed in the tetragonal phase. We conclude that the local fields cannot penetrate in the sample when the polarizability of freely moving cations boosts the dielectric constant up to ϵ = 120

Efficacy and Safety of a Distraction-Rotation Knee Brace (odra) in Medial Knee Osteoarthritis - a Phase Iii Randomised Controlled Trial (ergonomie Study)

IF 12.3550International audienceBackground : According to EULAR and OARSI guidelines, evidence is inconclusive for the symptomatic benefits of an unloader knee brace in medial knee osteoarthritis (OA).Objectives : The objective of this multicenter randomised controlled trial (RCT) (ClinicalTrials Id. NCT02765685) was to compare the efficacy and safety of the ODRA brace, a distraction-rotation custom-made knee brace versus usual care over one year in medial knee OA.Methods : Patients with symptomatic medial knee OA (VAS pain scores at rest >40/100 for the medial compartment) and Kellgren-Lawrence (KL) grade II-IV were randomised in two groups: brace group (ODRA +usual care) vs usual care alone (UCA). Patients were followed up every two months for one year. Usual care consisted of all the pharmacological and non-pharmacological treatments used for the management of knee OA. The primary end-point was the difference of VAS-pain between M0 and M12. Secondary end-points included patient global assessment of disease severity (PGA) on VAS,% of patients reaching the PASS (VAS-pain 20/100) thresholds at M12, KOOS scores, OA-specific quality of life questionnaire (OAKHQOL), as well as drug intake. Safety and compliance were evaluated by recording side effects and average knee brace duration of wear, respectively.Results : Overall 120 patients (57% women) from 7 centres were included. Their characteristics were the following: mean age 63.6±11.4 years; BMI 29.6±5.5 kg/m2; OA duration 5.8±6 years; 52% KL III; 21% KL IV. The VAS pain decrease was statistically higher in the ODRA group (from 61.9±17.4 (M0) to 38.8±25.3 (M12) than in the UCA group (54.9±18.2 to 45.5±23.8) in the intent to treat bivariate and multivariate analyses (delta VAS-pain: 13.1±4.9, p<0.01). At M12, ODRA patients experienced a significant higher improvement than the UCA patients for PGA, all KOOS domains and for 3 of 5 domains of OAKHQOL (Pain, Physical activities, Mental health). Patients reaching PASS threshold at M12 were 42% in ODRA group vs 27% in UCA group (OR=3.04; 95% CI: 1.11 to 8.30; p<0.05) and were 46% vs 28% for MCII respectively (OR=2.65, 95% CI: 1.01 to 6.96; p<0.05). The overall analgesic use decreased more frequently in the ODRA group at M12 than in the UCA group (32.7% vs 15.4%, p<0.05) except for NSAIDs, HA or steroid injections. The compliance was good: the brace was worn for a median [IQR] duration of 5.7 [4.0–7.0] hours a day between M0 and M6 and 5.3 [3.7–6.3] hours a day between M6 and M12. Non-serious side effects were more common in the ODRA group (p<0.05) which justified the definitive withdrawal of the brace in 8 ODRA patients (13%), mainly for cutaneous side effects.Conclusions : In this RCT, the use of the ODRA brace in addition to usual care was shown to be superior to usual care alone in reducing symptoms and improving quality of life of patients suffering from medial knee OA, with good compliance

Femto- to Microsecond Dynamics of Excited Electrons in a Quadruple Cation Perovskite

Quadruple cation mixed halide perovskite, GA0.015Cs0.046MA0.152FA0.787Pb(I0.815Br0.185)3, single crystals were grown for the first time using an inverse temperature crystallization process. Solar cell devices in n-i-p stack configuration using thin films of the same materials showed power conversion efficiency above 20%. Complementary time-resolved spectroscopy confirmed that polycrystalline thin films and single crystals identically composed exhibit similar carrier dynamics in the picosecond range. Cooling of excited carriers and bandgap renormalization occur on the same time scale of 200–300 fs. The radiative recombination coefficient (1.2 × 10–9 cm3/s) is comparable to values reported for a GaAs semiconductor. At low excitation density, a long carrier lifetime of 3.2 μs was recorded possibly due to the passivation of recombination centers. This study clarifies discrepancies about the lifetime of hot carriers, the impact of radiative recombination, and the role of recombination centers on solar cell performance. The quadruple cation perovskites displayed short time dynamics with slow recombination of charge carriers.acceptedVersionPeer reviewe