Insight into the role of guanidinium and cesium in triple cation lead halide perovskites

The overall impact of the partial replacement (5–15%) of methylammonium (MA)in the MAPbI3perovskite by cesium or guanidinium (Gua) cations to fabricatethinfilms of triple cation CsxGuayMA1–x–yPbI3perovskites is studied.The structural changes are investigated by using X-ray diffraction measurementsrevealing shrinkage or expansion of the unit cell upon Cs or Gua incorporation,respectively. The optoelectronic properties are characterized with photolumi-nescence (PL) time-resolved spectroscopy and the space charge limited current(SCLC) method. Shorter PL time constants are obtained for the samples with onlyCs, while longer PL decays are measured for the perovskites containing additionalGua cation. The SCLC measurements reveal a larger density of trap states in theCsxMA1–xPbI3perovskites compared to the MAPbI3material. The PSCs fabricatedwith the different mixed cation CsxGuayMA1–x–yPbI3perovskites reveal a goodcorrelation with the measured optoelectronic properties. The power conversionefficiency (PCE) improves from an average value of 18.6% for the MAPbI3to avalue of 20.0% for the Cs0.05Gua0.05MA0.90PbI3perovskite with a champion celldelivering 21.2%. On the opposite, the PCE decreases to a value of 17.3% for thedouble cation perovskite with Cs

Impedance analysis of perovskite solar cells: a case study

Metal halide perovskites are mixed electronic-ionic semiconductors with an extraordinary rich optoelectronic behavior and the capability to function very efficiently as active layers in solar cells, with a record efficiency surpassing 23% nowadays. In this work, we carry out an impedance spectroscopy analysis of two perovskite solar cells with quite distinct optical and electrical characteristics, i.e. MAPbI3 and CsPbBr3-based devices. The main aim of the analysis is to establish how, regardless the inherent complexity of the impedance spectrum due to ionic effects, information like ideality factors, recombination losses and the collection efficiency can be qualitative and quantitatively assessed from impedance experiments at operating conditions

Cellulose-Assisted Formation of 2D Hybrid Halide Perovskite Nanocrystals with Enhanced Stability for Light-Emitting Devices

A common approach to enhance the stability of metal halide perovskites (MHPs) implemented in optical and optoelectronic devices is to incorporate polymer additives into the perovskite layer. A β-(1,4) cellulose oligosaccharide (COS) synthesized by mechanocatalytic depolymerization of cellulose has been incorporated to films of the BA2MA4Pb5I16 (BA = n-butylammonium and MA = methylammonium) two-dimensional (2D) Ruddlesden-Popper (RP) hybrid perovskite. Scanning Electron Microscopy (SEM) images displayed a three-fold reduction of the 2D RP perovskite grains (≈30–40 nm), close to the quantum confinement scale. The analysis of the dark J–V curves of single carrier devices by using the space charge limited current (SCLC) method resulted in a rise of the defect concentration. A notable 14-fold increase in the photoluminescence (PL) signal at high COS content is detected. Moreover, the analysis of the temperature dependence PL measurements (80–300 K) resulted in a larger exciton binding energy, Eb = 180 to 370 meV, at high COS content. Light emitting diodes of the 2D RP perovskites (PeLEDs) are fabricated w/o the COS compound. The stability test performed under operation (5 V) displays 20 times higher operational lifetimes at high COS content while the luminance is also increased in the devices with the COS compound

Homeopathic Perovskite Solar Cells: Effect of Humidity during Fabrication on the Performance and Stability of the Device

Rapid degradation in humid environments is a major drawback of methylammonium lead iodide (CH3NH3PbI3), which is the archetypical component of perovskite solar cells. In this work, we have investigated the aging and degradation kinetics of CH3NH3PbI3 films and devices fabricated under controlled conditions as a function of relative humidity (RH) and compared their performance with those that were prepared under dry conditions. The aging and degradation kinetics is monitored by optical absorption and impedance spectroscopy measurements under monochromatic illumination at two different wavelengths. Aged devices show a substantial difference between the recombination rate under red and blue light illumination, which is attributed to the enhancement of local recombination routes upon aging. Interestingly, we observe that this feature is less pronounced in devices prepared under conditions of the highest RH of 50%. In general, we found that these devices keep their original electric properties and withstand a humid environment better. Chemical analysis by X-ray photoelectron spectroscopy reveals the presence of coordinating water in the CH3NH3PbI3 crystalline structure. This indicates that the presence of a small amount of water has a beneficial effect against degradation in a humid environment

Efficacy of clozapine versus standard treatment in adult individuals with intellectual disability and treatment-resistant psychosis (CLOZAID): study protocol of a multicenter randomized clinical trial

BackgroundIntellectual disability (ID) affects approximately 1% of the worldwide population and individuals with ID have a higher comorbidity with mental illness, and specifically psychotic disorders. Unfortunately, among individuals with ID, limited research has been conducted since ID individuals are usually excluded from mental illness epidemiological studies and clinical trials. Here we perform a clinical trial to investigate the effectiveness of clozapine in the treatment of resistant psychosis in individuals with ID. The article highlights the complexity of diagnosing and treating psychopathological alterations associated with ID and advocates for more rigorous research in this field.MethodsA Phase IIB, open-label, randomized, multicenter clinical trial (NCT04529226) is currently ongoing to assess the efficacy of oral clozapine in individuals diagnosed with ID and suffering from treatment-resistant psychosis. We aim to recruit one-hundred and fourteen individuals (N=114) with ID and resistant psychosis, who will be randomized to TAU (treatment as usual) and treatment-with-clozapine conditions. As secondary outcomes, changes in other clinical scales (PANSS and SANS) and the improvement in functionality, assessed through changes in the Euro-QoL-5D-5L were assessed. The main outcome variables will be analyzed using generalized linear mixed models (GLMM), assessing the effects of status variable (TAU vs. Clozapine), time, and the interaction between them.DiscussionThe treatment of resistant psychosis among ID individuals must be directed by empirically supported research. CLOZAID clinical trial may provide relevant information about clinical guidelines to optimally treat adults with ID and treatment-resistant psychosis and the benefits and risks of an early use of clozapine in this underrepresented population in clinical trials.Trial registrationClinicaltrials.gov: NCT04529226. EudraCT: 2020-000091-37

Strategies to improve the efficiency and stability of solar devices based on hybrid Perovskites

Este trabajo de Tesis Doctoral trata de la síntesis de perovskitas híbridas orgánicas-inorgánicas de halogenuros metálicos, así como de la fabricación de dispositivos fotovoltaicos basados en las mismas y su posterior caracterización. A lo largo de este trabajo se desarrollan tres estrategias destinadas a aumentar la estabilidad intrínseca de las perovskitas con el objetivo de mejorar la estabilidad y el rendimiento fotovoltaico de las células solares. La primera de ellas es conocida como ingeniería composicional, en la que se sustituye parcialmente el catión metilamonio (MA) de la perovskita tridimensional MAPbI3 por los cationes guanidinio (Gua) y cesio (Cs). La segunda estrategia consiste en la síntesis de perovskitas de baja dimensión, concretamente perovskitas híbridas quasi-bidimensionales tipo Ruddlesden-Popper. Por último, y como tercera estrategia, se considera la pasivación a partir de diferentes compuestos como moléculas orgánicas voluminosas que forman perovskitas de baja dimensión tipo Dion-Jacobson, nanopartículas plasmónicas de oro recubiertas por una capa de SiO2, y el oligosacárido β-(1,4) celulosa. Como prueba de concepto, se han fabricado diodos emisores de luz (LEDs) basados en determinadas configuraciones de perovskitas, persiguiendo el mismo objetivo que para las células solares.The work carried out in this Doctoral Thesis deals with the synthesis and characterization of the hybrid organic-inorganic metal halide perovskites, as well as the fabrication of photovoltaic devices based on those materials. Throughout this work, three strategies are developed to increase the intrinsic stability of halide perovskites and therefore the stability and photovoltaic performance of their solar cells. The first one is known as compositional engineering, in which the methylammonium (MA) cation is partially replaced in the three-dimensional MAPbI3 perovskite by the guanidinium (Gua) and cesium (Cs) cations. The second strategy consists of the synthesis of low-dimensional perovskites, specifically quasi-two-dimensional Ruddlesden- Popper perovskites. Finally, as the third strategy, passivation is considered using different compounds such as voluminous organic molecules that form low-dimensional perovskites of the Dion-Jacobson type, plasmonic gold nanoparticles coated with a layer of SiO2, and the β-(1,4) cellulose oligosaccharide. As a proof of concept, light-emitting diodes (LEDs) based on specific perovskite configurations have been fabricated, aiming for the same objective as in solar cells

A-Site Cation Engineering in 2D Ruddlesden–Popper (BA)2(MA1-xAx)2Pb3I10 Perovskite Films

The partial incorporation of large organic cations into the octahedral sites of 3D perovskites has been widely investigated but few works have reported their addition in 2D Ruddlesden–Popper (RP) perovskites. Here, the gradual substitution of the methylammonium (MA) cation in thin films of 2D RP perovskites (BA)(MA)PbI (BA = n-butylammonium) by guanidinium (Gua), dimethylammonium (DA), ethylammonium (EA), rubidium (Rb), propylammonium (PA), cesium (Cs) or formamidinium (FA) to synthesize mixed A-cation (BA)(MAA)PbI perovskites has been studied. The limit in the percentage of the A-site cation at which it is homogeneously incorporated in all n phases without destabilizing the overall structure is determined. It is found that the structural changes in the 2D RP perovskites may lead to modifications of the optoelectronic properties as larger bandgap (EA), blue-shift of the PL peak position (above the threshold), strong quenching of the PL (Cs) or reduced concentration of trap states (Gua and EA). Solar devices fabricated with the different mixed A-cation 2D RP display an enhanced performance for those perovskites containing low percentages of Gua or EA cations. This characterization is very valuable to correlate the size and shape of the A-cation with the changes of the properties of the material.This work was supported by National Science Foundation grant DMS-135888

Relaxing the Goldschmidt Tolerance Factor: Sizable Incorporation of the Guanidinium Cation into a Two-Dimensional Ruddlesden-Popper Perovskite

The two-dimensional (2D) hybrid perovskites, in particular the Ruddlesden-Popper (RP) phase, exhibit excellent optoelectronic properties, higher flexibility in the employed large organic cations, and an enhanced stability against the environmental agents compared to the three-dimensional (3D) perovskites. However, the small organic cations inserted into the octahedral voids have been limited so far to those three fulfilling the Goldschmidt tolerance factor (t) despite the relaxed structure of the 2D RP perovskites. In this work, the incorporation of the large guanidinium (Gua) cation into the octahedral sites of the "perovskite slabs"has been explored for the first time in 2D RP perovskites. Thus, the methylammonium (MA) cation in the PEA2MA2Pb3I10 perovskite (PEA = phenylethylammonium) has been gradually substituted by the Gua cation to synthesize thin films of the mixed-cation PEA2(MA1-xGuax)2Pb3I10 perovskite. X-ray diffraction (XRD) and grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements have revealed a regular expansion of the unit cell when increasing the Gua content up to 90%, proving the sequential insertion into the lattice of the Gua having a larger ionic radius than that of the MA cation. Furthermore, the preferential orientation of the PEA2MA2Pb3I10 perovskite films with the (hk0) planes parallel to the substrate is maintained up to a limit value of 60% Gua content. Importantly, the combined analysis of the steady-state and time-resolved absorption and photoluminescence (PL) spectra has revealed a change in the distribution of the n-members of the 2D RP perovskites toward phases with lower n values upon increasing the Gua content. The position and intensity of the photoluminescence can be modulated within the low-dimensional perovskites (n = 2, 3, 4, and 5) at high Gua content (≥70%). We have fabricated solar cells based on the mixed-cation PEA2(MA1-xGuax)2Pb3I10 perovskites with power conversion efficiency (PCE) values similar to those of the reference cell (∼2.5%) up to percentages of Gua of 20%. The unencapsulated devices have shown a significant enhancement in the stability after 750 h, demonstrating the positive effect of the Gua cation on the degradation of the 2D RP perovskites.G.d.M. thanks the Ministry of Economy and Competitiveness for a “Ramón y Cajal” contract (RYC-2013-12772). S.R.-T. thanks the Ministry of Education, Culture and Sport for an FPU fellowship (FPU18/04452). This work was financially supported by the Ministerio de Economía y Competitividad (MINECO) through project CTQ2017-84221-R, cofinanced with the FEDER funds. We are grateful to Dr. Eduardo Espinosa Victor and Prof. Alejandro Rodríguez Pascual for their assistance with infrared spectroscopy. We also want to thank Prof. Juan Antonio Anta and Dr. Lidia Contreras-Bernal for their help in the fabrication of the solar devices and with the SEM measurements. Finally, we would like to appreciate the support from Dr. Eva García-Frutos in the realization of the NMR experiment

Nuevos datos sobre la distribución de Orthetrum trinacria (Sélys, 1841) (Odonata: Libellulidae) en el sur de la Península Ibérica.

Se aportan nuevos registros de Orthetrum trinacria (Sélys, 1841) (Odonata: Libellulidae) en el sur de la Península Ibérica, constatando la reproducción de esta especie en Andalucía mediante el hallazgo de una exuvia y de ejemplares adultos inmaduros.New records of Orthetrum trinacria are reported, being proved the reproduction of this species in Andalusia by the finding of an exuvia and teneral adults