Preferred Growth Direction by PbS Nanoplatelets Preserves Perovskite Infrared Light Harvesting for Stable, Reproducible, and Efficient Solar Cells

Formamidinium-based perovskite solar cells (PSCs) present the maximum theoretical efficiency of the lead perovskite family. However, formamidinium perovskite exhibits significant degradation in air. The surface chemistry of PbS has been used to improve the formamidinium black phase stability. Here, the use of PbS nanoplatelets with (100) preferential crystal orientation is reported, to potentiate the repercussion on the crystal growth of perovskite grains and to improve the stability of the material and consequently of the solar cells. As a result, a vertical growth of perovskite grains, a stable current density of 23 mA cm(-2), and a stable incident photon to current efficiency in the infr…

Manipulating spontaneous emission of the CsPbI3 Perovskite NCs using hybrid (HMM-Mie resonator) structures

Boosting Long-Term Stability of Pure Formamidinium Perovskite Solar Cells by Ambient Air Additive Assisted Fabrication

Due to the high industrial interest for perovskite-based photovoltaic devices, there is an urgent need to fabricate them under ambient atmosphere, not limited to low relative humidity (RH) conditions. The formamidinium lead iodide (FAPI) perovskite α-black phase is not stable at room temperature and is challenging to stabilize in an ambient environment. In this work, we show that pure FAPI perovskite solar cells (PSCs) have a dramatic increase of device long-term stability when prepared under ambient air compared to FAPI PSCs made under nitrogen, both fabricated with N-methylpyrrolidone (NMP). The T80 parameter, the time in which the efficiency drops to 80% of the initial value, increases f…

Outstanding nonlinear optical properties of methylammonium- and Cs-PbX3 (X = Br, I, and Br–I) perovskites: Polycrystalline thin films and nanoparticles

Metal Halide Perovskites (MHPs) have arisen as promising materials to construct cost-effective photovoltaic and light emission devices. The study of nonlinear optical properties of MHPs is necessary to get similar success in nonlinear photonic devices, which is practically absent in the literature. The determination of the third order nonlinear coefficients is typically done by the Z-scan technique, which is limited by the scattering of polycrystalline thin films. In this work, we have studied nonlinear optical properties of polycrystalline CH3NH3PbX3 (MAPbX3) thin films and colloidal CsPbX3 nanoparticles with three different bandgaps (X3 = I3, Br3, and Br1.5I1.5). Their bright generation o…

The role of surface chemical states on the photocatalytic behavior of all-inorganic mixed halide perovskite nanocrystals

Enhanced nanoscopy of individual CsPbBr3 perovskite nanocrystals using dielectric sub-micrometric antennas

We demonstrate an efficient, simple, and low-cost approach for enhanced nanoscopy in individual green emitting perovskite (CsPbBr3) nanocrystals via TiO2 dielectric nanoantenna. The observed three- to five-fold emission enhancement is attributed to near-field effects and emission steering promoted by the coupling between the perovskite nanocrystals and the dielectric sub-micrometric antennas. The dark-field scattering configuration is then exploited for surface-enhanced absorption measurements, showing a large increase in detection sensitivity, leading to the detection of individual nanocrystals. Due to the broadband spectral response of the Mie sub-micrometric antennas, the method can be e…

Role of Self-Absorption in the Photoluminescence Waveguided along CsPbBr3 Perovskite Nanocrystals Thin Films

During the last years, perovskite nanocrystals (PNCs) have been intensively studied as nanomaterials with excellent light absorption/emission properties. For example, PNCs have been successfully applied in solar cells, where the high absorption coefficient above the band gap increases the conversion efficiencies; or in optical sources, where the high quantum yield of emission at room temperature allows a low threshold of stimulated emission. In this scenario, an optical waveguide represents a suitable platform to enhance their electrooptical properties and to integrate different photonic functionalities. However, propagation of light along close packed films of PNCs is usually restricted to…

Amplified Spontaneous Emission in Thin Films of CsPbX3 Perovskite Nanocrystals

During the last years, Metal Halide Perovskites (MHPs) have attracted special attention as an efficient conversion films for photovoltaics, or excellent gain media to construct optical sources. In spite of the fact that most of the works have been focussed on CH 3 NH 3 PbX 3 (X=Cl, Br, I) polycrystalline thin films, MHP can be also synthesized as colloidal nanocrystals. In particular, caesium lead halide perovskite CsPbX 3 nanocrystals (NCs) revealed extraordinary properties for optoelectronics. With a high quantum yield of emission (>90%) at room temperature and linewidths less than 100 meV, CsPbX 3 NCs have demonstrated favourable characteristics for active photonics. Indeed, thin films o…

Single-Exciton Amplified Spontaneous Emission in CsPbX3 (X = Br, I) Perovskite Nanocrystals

Homogeneous and inhomogeneous broadening in single perovskite nanocrystals investigated by micro-photoluminescence

Abstract Metal halides with perovskite crystalline structure have given rise to efficient optoelectronic and photonic devices. In the present work, we have studied the light emission properties of single CsPbBr3 and CsPbI3 semiconductor perovskite nanocrystals (PNCs), as the basis for a statistical analysis of micro-photoluminescence (micro-PL) spectra measured on tens of them. At room temperature, the linewidth extracted from PL spectra acquired in dense films of these nanocrystals is not very different from that of micro-PL measured in single nanocrystals. This means that the homogeneous linewidth due to exciton-phonon interaction is comparable or larger than the inhomogeneous effect asso…

High Optical Performance of Cyan‐Emissive CsPbBr3 Perovskite Quantum Dots Embedded in Molecular Organogels

This is the pre-peer reviewed version of the following article: High Optical Performance of Cyan‐Emissive CsPbBr3 Perovskite Quantum Dots Embedded in Molecular Organogels, which has been published in final form at https://doi.org/10.1002/adom.202001786. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions." Perovskite quantum dots (PQDs) have fascinating optoelectronic properties, such as high photoluminescence quantum yield (PLQY) for a broad range of materials, and the possibility to obtain different bandgaps with the same material or halide combinations. Nevertheless, blue‐emissive materials generally present…

Recycled Photons Traveling Several Millimeters in Waveguides Based on CsPbBr 3 Perovskite Nanocrystals

Reabsorption and reemission of photons, or photon recycling (PR) effect, represents an outstanding mechanism to enhance the carrier and photon densities in semiconductor thin films. This work demonstrates the propagation of recycled photons over several mm by integrating a thin film of CsPbBr3 nanocrystals into a planar waveguide. An experimental set-up based on a frequency modulation spectroscopy allows to characterize the PR effect and the determination of the effective decay time of outcoupled photons. A correlation between the observed photoluminescence redshift and the increase of the effective decay time is demonstrated, which grows from 3.5 to near 9 ns in the best device. A stochast…

Enabling long-term stable FAPb1-xSrxI3 quantum dots with high optical performance: the effect of Sr2+ doping

Optical Amplification in Hollow-Core Negative-Curvature Fibers Doped with Perovskite CsPbBr3 Nanocrystals

| openaire: EC/H2020/820423/EU//S2QUIP We report a hollow-core negative-curvature fiber (HC-NCF) optical signal amplifier fabricated by the filling of the air microchannels of the fiber with all-inorganic CsPbBr3 perovskite nanocrystals (PNCs). The optimum fabrication conditions were found to enhance the optical gain, up to +3 dB in the best device. Experimental results were approximately reproduced by a gain assisted mechanism based on the nonlinear optical properties of the PNCs, indicating that signal regeneration can be achieved under low pump powers, much below the threshold of stimulated emission. The results can pave the road of new functionalities of the HC-NCF with PNCs, such as op…

Signal Amplification in CsPbBr3 Nanoparticle-Doped Photonic Crystal Fibers

Nanoparticles (NPs) have been proved for various photonic and optoelectronic applications with superior performance. Doping holey-fibers with colloidal NPs is an idea with precedents in the optical literature. For example, CdZnS/ZnS core-shell quantum dots (QDs) based lasers at visible wavelengths [1, 2]; and PbS QDs doped fiber amplifiers operating at telecommunication wavelengths [3]. In this paper we harness the potential of photonic crystal fibers (PCFs) doped with chemically synthesized CsPbBr 3 Colloidal-NPs [4] to demonstrate gain functionalities in all-fiber optical microdevices.

Improving Long Term Stability of Pure Formamidinium Perovskite Solar Cells by Ambient Air Additive Assisted Fabrication

Purcell Enhancement and Wavelength Shift of Emitted Light by CsPbI3 Perovskite Nanocrystals Coupled to Hyperbolic Metamaterials

Manipulation of the exciton emission rate in nanocrystals of lead halide perovskites (LHPs) was demonstrated by means of coupling of excitons with a hyperbolic metamaterial (HMM) consisting of alternating thin metal (Ag) and dielectric (LiF) layers. Such a coupling is found to induce an increase of the exciton radiative recombination rate by more than a factor of three due to the Purcell effect when the distance between the quantum emitter and HMM is nominally as small as 10 nm, which coincides well with the results of our theoretical analysis. Besides, an effect of the coupling-induced long wavelength shift of the exciton emission spectrum is detected and modeled. These results can be of i…

Engineering Sr-doping for enabling long-term stable FAPb1xSrxI3 quantum dots with 100% photoluminescence quantum yield

The Pb substitution in quantum dots (PQDs) with lesser toxic metals has been widely searched to be environmentally friendly, and be of comparable or improved performance compared to the lead-perovskite. However, the chemical nature of the lead substitute influences the incorporation mechanism into PQDs, which has not been explored in depth. In this work, we analyzed Sr-doping-induced changes in FAPbI3 perovskites by studying the optical, structural properties and chemical environment of FAPb1−xSrxI3 PQDs. The substitution of Pb by 7 at% Sr allows us to achieve FAPb1−xSrxI3 PQDs with 100% PLQY, high stability for 8 months under a relative humidity of 40–50%, and T80 = 6.5 m…

Single-Exciton Amplified Spontaneous Emission in Thin Films of CsPbX3 (X = Br, I) Perovskite Nanocrystals

CsPbX3 perovskite nanocrystals (PNCs) have emerged as an excellent material for stimulated emission purposes, with even more prospective applications than conventional colloidal quantum dots. However, a better understanding of the physical mechanisms responsible for amplified spontaneous emission (ASE) is required to achieve more ambitious targets (lasing under continuous wave optical or electrical excitation). Here, we establish the intrinsic mechanisms underlying ASE in PNCs of three different band gaps (CsPbBr3, CsPbBr1.5I1.5, and CsPbI3). Our characterization at cryogenic temperatures does not reveal any evidence of the biexciton mechanism in the formation of ASE. Instead, the measured …

Morphology and Band Structure of Orthorhombic PbS Nanoplatelets: An Indirect Band Gap Material

PbS quantum dots and nanoplatelets (NPLs) are of enormous interest in the development of optoelectronic devices. However, some important aspects of their nature remain unclear. Recent studies have revealed that colloidal PbS NPLs may depart from the rock-salt crystal structure of bulk and form an orthorhombic (Pnma) modification instead. To gain insight into the implications of such a change over the optoelectronic properties, we have synthesized orthorhombic PbS NPLs and determined the lattice parameters by means of selected area electron diffraction measurements. We have then calculated the associated band structure using density functional theory with Perdew–Burke–Ernzerhof functional fo…

Interpretation of the photoluminescence decay kinetics in metal halide perovskite nanocrystals and thin polycrystalline films

Abstract In this paper we present critical analysis of different points of view on interpretation of the photoluminescence (PL) decay kinetics in lead halide perovskites prepared in the form of well passivated nanocrystals (PNCs) or thin polycrystalline layers. In addition to the literature data, our own measurements are also considered. For PNCs, a strong dependence of the PL lifetimes on the type of passivating ligand was observed with a consistently high PL quantum yield. It is shown that such ligand effects, as well as a decrease in the PL lifetime with decreasing temperature, are well qualitatively explained by the phenomenological model of thermally activated delayed luminescence, in …

Controlling the Phase Segregation in Mixed Halide Perovskites through Nanocrystal Size

Mixed halide perovskites are one of the promising candidates in developing solar cells and light-emitting diodes (LEDs), among other applications, because of their tunable optical properties. Nonetheless, photoinduced phase segregation, by formation of segregated Br-rich and I-rich domains, limits the overall applicability. We tracked the phase segregation with increasing crystalline size of CsPbBr3–xIx and their photoluminescence under continuous-wave laser irradiation (405 nm, 10 mW cm–2) and observed the occurrence of the phase segregation from the threshold size of 46 ± 7 nm. These results have an outstanding agreement with the diffusion length (45.8 nm) calculated also experimentally f…

Unravelling the Photocatalytic Behavior of All-Inorganic Mixed Halide Perovskites: The Role of Surface Chemical States

Within the most mesmerizing materials in the world of optoelectronics, mixed halide perovskites (MHPs) have been distinguished because of the tunability of their optoelectronic properties, balancing both the light-harvesting efficiency and the charge extraction into highly efficient solar devices. This feature has drawn the attention of analogous hot topics as photocatalysis for carrying out more efficiently the degradation of organic compounds. However, the photo-oxidation ability of perovskite depends not only on its excellent light-harvesting properties but also on the surface chemical environment provided during its synthesis. Accordingly, we studied the role of surface chemical states …