Examinando por Autor "Redondo-Obispo, Carlos"

Mostrando 1 - 4 de 4

Enhanced Nonlinear Optical Coefficients of MAPbI3 Thin Films by Bismuth Doping
(ACS, 2020-02-18) Redondo-Obispo, Carlos; Suárez, Isaac; Quesada, Sergio J; Ripolles, Teresa S; Martínez-Pastor, Juan P; Álvarez, Angel L; de Andrés, Alicia; Coya, Carmen
The poor photostability under ambient conditions of hybrid halide perovskites has hindered their recently explored promising nonlinear optical properties. Here, we show how Bi3+ can partially substitute Pb2+ homogeneously in the commonly studied MAPbI3, improving both environmental stability and photostability under high laser irradiation. Bi content around 2 atom % produces thin films where the nonlinear refractive (n2) and absorptive coefficients (β), which modify the refractive index (Δn) of the material with light fluence (I), increase up to factors of 4 and 3.5, respectively, compared to undoped MAPbI3. Higher doping inhibits the nonlinear parameters; however, the samples show higher fluence damage thresholds. Thus, these results provide a road map on how MAPbI3 can be engineered for practical cost-effective nonlinear applications by means of Bi doping, including optical limiting devices and multiple-harmonic generation into optoelectronics devices.
Huge Photo-Stability Enhancement in Bismuth Doped Methylammonium Lead Iodide Hybrid Perovskites by Light Induced Transformation
(ACS, 2019-04-26) Bartolomé, Javier; Climent-Pascual, Esteban; Redondo-Obispo, Carlos; Álvarez, Angel L; de Andrés, Alicia; Coya, Carmen
The doping strategy of hybrid perovskites is being extensively explored not only for higher efficiency but also to overcome issues in photovoltaic materials such as self-degradation pathways in an ambient atmosphere or under visible irradiation. Here, BiI3 is introduced in the synthesis of MAPbI3 films (MA: CH3–NH3+) to stabilize the material. Around 25% of nominal Bi3+ is accommodated in the perovskite structure, producing a shrinking of the unit cell and a small increase of the band gap. The presence of empty Bi gap states quenches the 770 nm red interband emission and results in a near-infrared emission at 1100 nm. However, high enough visible irradiation density induces a progressive segregation of Bi3+ out of the perovskite lattice and promotes the re-emergence of the red emission. This emission is blue-shifted, and its intensity increases strongly with time until it reaches a saturation value which remains stable in the transformed films for extremely high power densities, around 1000 times higher than for undoped samples. We propose that the underlying processes include the formation of BiI3 and BiOI, probably at the surface of the crystals, hampering the usual decomposition pathways into PbI2 and PbOx for undoped MAPbI3. These results provide a new path for obtaining highly stable materials which would allow an additional boost of hybrid perovskite-based optoelectronics.
Interface Engineering in Perovskite Solar Cells by low concentration of PEAI solution in the antisolvent step
(Wiley, 2021-12-03) Ripolles, Teresa S; Serafini, Patricio; Redondo-Obispo, Carlos; Climent-Pascual, Esteban; Masi, Sofía; Mora-Seró, Ivan; Coya, Carmen
In spite of the outstanding properties of metal halide perovskites, its polycrystalline nature induces a wide range of structural defects that results in charge losses that affect the final device performance and stability. Herein, a surface treatment is used to passivate interfacial vacancies and improve moisture tolerance. A functional organic molecule, phenylethyl ammonium iodide (PEAI) salt, is dissolved with the antisolvent step. The additive used at low concentration does not induce formation of low-dimensional perovskites species. Instead, the organic halide species passivate the surface of the perovskite and grain boundaries, which results in an effective passivation. For sake of generality, this facile solution-processed synthesis was studied for halide perovskite with different compositions, the standard perovskite MAPbI3, and double cation perovskites, MA0.9Cs0.1PbI3 and MA0.5FA0.5PbI3, increasing the average photoconversion efficiency compared to the reference cell by 18%, 32%, and 4% respectively, observed for regular, n-i-p, and inverted, p-i-n, solar cell configurations. This analysis highlights the generality of this approach for halide perovskite materials in order to reduce nonradiative recombination as observed by impedance spectroscopy.
Selective Growth of MAPbBr3 Rounded Microcrystals on Micro-Patterned Single-Layer Graphene Oxide/Graphene Platforms with Enhanced Photo-Stability
(MDPI, 2023-08-16) Bartolomé, Javier; Vila, María; Redondo-Obispo, Carlos; de Andrés, Alicia; Coya, Carmen
The synergistic combination of hybrid perovskites with graphene-related materials is leading to optoelectronic devices with enhanced performance and stability. Still, taking advantage of the solution processing of perovskite onto graphene is especially challenging. Here, MAPbBr3 perovskite is grown on single-layer graphene/graphene oxide (Gr/GO) patterns with 120 µm periodicity using a solution-processed method. MAPbBr3 rounded crystals are formed with sizes ranging from nanometers to microns, either forming continuous films or dispersed particles. A detailed morphological and structural study reveals a fully oriented perovskite and very different growth habits on the Gr/GO micro-patterns, which we relate to the substrate characteristics and the nucleation rate. A simple method for controlling the nucleation rate is proposed based on the concentration of the precursor solution and the number of deposited perovskite layers. The photoluminescence is analyzed in terms of the crystal size, strain, and structural changes observed. Notably, the growth on top of Gr/GO leads to a huge photostability of the MAPbBr3 compared with that on glass. Especially outstanding is that of the microcrystals, which endure light densities as high as 130 kW/cm2. These results allow for anticipating the design of integrated nanostructures and nanoengineered devices by growing high-stability perovskite directly on Gr/GO substrates.