18 research outputs found
A dual-phase architecture for efficient amplified spontaneous emission in lead iodide perovskites
We report a way to overcome Auger recombination in lead iodide perovskites by investigating the domain structure forming below the phase transition temperature
Waveguide-plasmon polaritons enhance transverse magneto-optical Kerr effect
Magneto-optical effects in ferrimagnetic or ferromagnetic materials are usually too weak for potential applications. The transverse magneto-optical Kerr effect (TMOKE) in ferromagnetic films is typically on the order of 0.1%. Here, we demonstrate experimentally the enhancement of TMOKE due to the interaction of particle plasmons in gold nanowires with a photonic waveguide consisting of magneto- optical material, where hybrid waveguide-plasmon polaritons are excited. We achieve a large TMOKE that modulates the transmitted light intensity by 1.5%, accompanied by high transparency of the system. Our concept may lead to novel devices of miniaturized photonic circuits and switches, which are controllable by an external magnetic field
17.6% stabilized efficiency in low-temperature processed planar perovskite solar cells
We present here a planar perovskite solar cell with a stabilized power conversion efficiency (PCE) of 17.6% at the maximum power point and a PCE of 17% extracted from quasi-static JâV with an open-circuit voltage of 1.11 V. Such excellent figures of merit can be achieved by engineering a solution-processed electron buffer layer that does not require high temperature steps. A compact thin film of perovskite absorber is grown onto a PCBM-based electron extraction layer by implementing a novel two-step procedure which preserves the soluble organic interlayer during the deposition of successive layers. We demonstrate that efficient charge extraction is the key for high steady state efficiency in perovskite solar cells with a highly integrable architecture
Exciton-Polaron Spectral Structures in Two-Dimensional Hybrid Lead-Halide Perovskites
© 2018 American Physical SocietyDOI: 10.1103/PhysRevMaterials.2.064605https://doi.org/10.1103/physrevmaterials.2.064605Owing to both electronic and dielectric confinement effects, two-dimensional organic-inorganic hybrid
perovskites sustain strongly bound excitons at room temperature. Here, we demonstrate that there are nonnegligible
contributions to the excitonic correlations that are specific to the lattice structure and its polar
fluctuations, both of which are controlled via the chemical nature of the organic countercation. We present
a phenomenological yet quantitative framework to simulate excitonic absorption line shapes in single-layer
organic-inorganic hybrid perovskites, based on the two-dimensionalWannier formalism.We include four distinct
excitonic states separated by 35 ± 5 meV, and additional vibronic progressions. Intriguingly, the associated
Huang-Rhys factors and the relevant phonon energies show substantial variation with temperature and the nature
of the organic cation. This points to the hybrid nature of the line shape, with a form well described by a Wannier
formalism, but with signatures of strong coupling to localized vibrations, and polaronic effects perceived through
excitonic correlations. Our work highlights the complexity of excitonic properties in this class of nanostructured
materials
Charge Trapping Dynamics in PbS Colloidal Quantum Dot Photovoltaic Devices
International audienceThe efficiency of solution-processed colloidal quantum dot (QD) based solar cells is limited by poor charge transport in the active layer of the device, which originates from multiple trapping sites provided by QD surface defects. We apply a recently developed ultrafast electro-optical technique, pump-push photocurrent spectroscopy, to elucidate the charge trapping dynamics in PbS colloidal-QD photovoltaic devices at working conditions. We show that IR photoinduced absorption of QD in the 0.2-05 eV region is partly associated with immobile charges, which can be optically detrapped in our experiment. Using this absorption as a probe, we observe that the early trapping dynamics strongly depend on the nature of the ligands used for QD passivation, while it depends only slightly on the nature of the electron-accepting layer. We find that weakly bound states, with a photon-activation energy of 0.2 eV, are populated instantaneously upon photoexcitation. This indicates that the photogenerated states show an intrinsically bound-state character, arguably similar to charge-transfer states formation in organic photovoltaic materials. Sequential population of deeper traps (activation energy 03-05 eV) is observed on the similar to 0.1-10 ns time scales, indicating that most of carrier trapping occurs only after substantial charge relaxation/transport. The reported study disentangles fundamentally different contributions to charge trapping dynamics in the nanocrystal-based optoelectronic devices and can serve as a useful tool for QD solar cell development
Charge Trapping Dynamics in PbS Colloidal Quantum Dot Photovoltaic Devices
The efficiency of solution-processed colloidal quantum dot (QD) based solar cells is limited by poor charge transport in the active layer of the device, which originates from multiple trapping sites provided by QD surface defects. We apply a recently developed ultrafast electro-optical technique, pump-push photocurrent spectroscopy, to elucidate the charge trapping dynamics in PbS colloidal-QD photovoltaic devices at working conditions. We show that IR photoinduced absorption of QD in the 0.2â0.5 eV region is partly associated with immobile charges, which can be optically detrapped in our experiment. Using this absorption as a probe, we observe that the early trapping dynamics strongly depend on the nature of the ligands used for QD passivation, while it depends only slightly on the nature of the electron-accepting layer. We find that weakly bound states, with a photon-activation energy of 0.2 eV, are populated instantaneously upon photoexcitation. This indicates that the photogenerated states show an intrinsically bound-state character, arguably similar to charge-transfer states formation in organic photovoltaic materials. Sequential population of deeper traps (activation energy 0.3â0.5 eV) is observed on the âŒ0.1â10 ns time scales, indicating that most of carrier trapping occurs only after substantial charge relaxation/transport. The reported study disentangles fundamentally different contributions to charge trapping dynamics in the nanocrystal-based optoelectronic devices and can serve as a useful tool for QD solar cell development
Fully Solution-Processed nâiâp-Like Perovskite Solar Cells with Planar Junction: How the Charge Extracting Layer Determines the Open-Circuit Voltage
Fully solution-processed direct perovskite solar cells with a planar junction are realized by incorporating a cross-linked [6,6]-phenyl-C61-butyric styryl dendron ester layer as an electron extracting layer. Power conversion efficiencies close to 19% and an open-circuit voltage exceeding 1.1 V with negligible hysteresis are delivered. A perovskite film with superb optoelectronic qualities is grown, which reduces carrier recombination losses and hence increases V oc
Stable Biexcitons In Two-Dimensional Metal-Halide Perovskites With Strong Dynamic Lattice Disorder
© 2018 American Physical SocietyDOI: 10.1103/PhysRevMaterials.2.034001https://doi.org/10.1103/physrevmaterials.2.034001With strongly bound and stable excitons at room temperature, single-layer, two-dimensional organic-inorganic
hybrid perovskites are viable semiconductors for light-emitting quantum optoelectronics applications. In such
a technological context, it is imperative to comprehensively explore all the factorsâchemical, electronic,
and structuralâthat govern strong multiexciton correlations. Here, by means of two-dimensional coherent
spectroscopy, we examine excitonic many-body effects in pure, single-layer (PEA)2PbI4 (PEA = phenylethylammonium).
We determine the binding energy of biexcitonsâcorrelated two-electron, two-hole quasiparticlesâto
be 44 ± 5meV at room temperature. The extraordinarily high values are similar to those reported in other strongly
excitonic two-dimensional materials such as transition-metal dichalcogenides. Importantly, we show that this
binding energy increases by âŒ25% upon cooling to 5 K. Our work highlights the importance of multiexciton
correlations in this class of technologically promising, solution-processablematerials, in spite of the strong effects
of lattice fluctuations and dynamic disorder