Resonant Photocurrent Generation in Dye-Sensitized Periodically Nanostructured Photoconductors by Optical Field Confinement Effects

Herein we show experimental evidence of resonant photocurrent generation in dye-sensitized periodically nanostructured photoconductors, which is achieved by spectral matching of the sensitizer absorption band to different types of localized photon modes present in either periodic or broken symmetry structures. Results are explained in terms of the calculated spatial distribution of the electric field intensity within the configurations under analysis.Unión Europea FP7 / 2007-2013Convenio de subvención ERC 307081 (POLIGHT)Ministerio de Economía y Competitividad MAT2011- 23593CONSOLIDER HOPE CSD2007-00007Junta de Andalucía FQM3579Junta de Andalucía FQM524

Solution processed high refractive index contrast distributed Bragg reflectors

We have developed a method to alternate porous and dense dielectric films in order to build high refractive index contrast distributed Bragg reflectors (DBRs) capable of reflecting very efficiently in a targeted spectral range employing a small number of layers in the stack. Porous layers made of SiO2 nanoparticles and compact sol–gel processed TiO2 layers are sequentially deposited. The key to the preservation of porosity of every other layer during the deposition process is the use of a sacrificial layer of polystyrene that prevents the infiltration of the interstitial voids between nanoparticles with the homogeneous solution of TiO2 precursors. Our approach allows preparing a series of DBRs operating along the whole visible spectral range. Reflectance values as high as 90% are achieved from only seven layers. The particular distribution of porosity along one direction gives rise to an interesting interplay between the optical properties of the system and the vapor pressure in the surrounding atmosphere, which we foresee could be put into practice in gas sensing devices.España, Ministerio de Economía y Competitividad MAT2014 54852-REspaña, European Union’s Seventh Framework Programme FP7/2007–2013)/ER

Optical design of all-perovskite tandem solar cells

We present a thorough analysis of the optical properties of CH 3NH 3Sn xPb1-x I 3 films, providing the field with definitive insights about the possibilities of these materials for perovskite solar cells of superior efficiency

Environmental Effects on the Photophysics of Organic–Inorganic Halide Perovskites

The photophysical properties of films of organic–inorganic lead halide perovskites under different ambient conditions are herein reported. We demonstrate that their luminescent properties are determined by the interplay between photoinduced activation and darkening processes, which strongly depend on the atmosphere surrounding the samples. We have isolated oxygen and moisture as the key elements in each process, activation and darkening, both of which involve the interaction with photogenerated carriers. These findings show that environmental factors play a key role in the performance of lead halide perovskites as efficient luminescent materials.Unión Europea FP7/2007-2013Ministerio de Economía y Competitividad MAT2014-54852-

Photophysical Analysis of the Formation of Organic–Inorganic Trihalide Perovskite Films: Identification and Characterization of Crystal Nucleation and Growth

In this work we demonstrate that the different processes occurring during hybrid organic–inorganic lead iodide perovskite film formation can be identified and analyzed by a combined in situ analysis of their photophysical and structural properties. Our observations indicate that this approach permits unambiguously identifying the crystal nucleation and growth regimes that lead to the final material having a cubic crystallographic phase, which stabilizes to the well-known tetragonal phase upon cooling to room temperature. Strong correlation between the dynamic and static photoemission results and the temperature-dependent X-ray diffraction data allows us to provide a description and to establish an approximate time scale for each one of the stages and their evolution. The combined characterization approach herein explored yields key information about the kinetics of the process, such as the link between the evolution of the defect density during film formation, revealed by a fluctuating photoluminescence quantum yield, and the gradual changes observed in the PbI2-related precursor structure.Unión Europea Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement No. 307081 (POLIGHT)España, Ministerio de Economía y Competitividad Grants MAT2014- 54852-R and MAT2012-31659España, Comunidad de Madrid programme S2013/MIT-274

3D internal reconstruction of the case study. Laboratory Investigations

11 páginas; 8 figurasThe main objective of the Heritage Within (HWITHIN) research project is to investigate what is hidden to our naked eye. One of the core actions of the project was to explore the use of Ground Penetrating Radar (GPR) and ultrasonic acoustic tomography to document and reconstruct precisely the interior of the constructive elements, almost on a stone-by-stone basis. However, precisely because it is not visible, the results obtained and the conclusions drawn cannot be verified with the reality. In the case of the Carmo Convent, the structural elements under investigations are the neogothic compound piers of the main nave, reconstructed after the 1755 earthquake. There is insufficient information on the layout of the interior morphology of the pillar’s cross-section. Additionally, finding relatable examples to compare to the compound pillars at the Carmo Convent are quite minimal, making it complicated for even initial assumptions to be established. Therefore, the team decided to construct 1:1 stone replicas of parts of the neogothic stone masonry pillars (the shaft and the pedestal). The specimens were used to assess the feasibility and efficiency of the non-destructive tests applied (GPR and acoustic tomography) to determine the layout of their internal morphology. Since the cross- section of the real pillars of the Carmo Convent is unknown, the replica only precisely depicts the exterior layout of the columns. The shapes of the stones were established on initial guesses based on literature review. Once the limestones were cut, several cross-sectional set-ups were prepared, mainly accounting for a wide range of possible interior core materials (from fully empty core to a solid limestone block filling). Acoustic tomography was carried out for each assembly so that accurate comparisons between the tomographic maps could be made. Moreover, given the known inner composition of the laboratory specimens, the results can help to understand the potential of the tomographic techniques by comparing the results with the expected visible interior. The present chapter shows some of the results obtained during the laboratory investigations, which were essential to interpret the ultrasonic tomography performed on-site at the old convent. The results confirm the potential of acoustic tomography techniques to convey an accurate idea of the cross-sectional elements within the pillar. The tomographic maps may not provide enough precision to determine exact dimensions of the materials and elements within the cross-section, but they can be complemented with GPR investigations and is always useful in a qualitative way, as it can provide information about the structural integrity of the materials and their arrangement.This publication shows the results of the Heritage Within (HWITHIN) European Research Project (Project Reference: 614719-CREA-1- 2019-1-PT-CROSS-SECT-INNOVLAB), co-funded by the Creative Europe Programme of the European Union, under the Cross-sectorial subprogramme, Bridging culture and audiovisual content through digital action

Optical analysis of CH3NH3SnxPb1–xI3 absorbers: a roadmap for perovskite-on-perovskite tandem solar cells

Organic–inorganic perovskite structures in which lead is substituted by tin are exceptional candidates for broadband light absorption. Herein we present a thorough analysis of the optical properties of CH3NH3SnxPb1–xI3 films, providing the field with definitive insights about the possibilities of these materials for perovskite solar cells of superior efficiency. We report a user's guide based on the first set of optical constants obtained for a series of tin/lead perovskite films, which was only possible to measure due to the preparation of optical quality thin layers. According to the Shockley–Queisser theory, CH3NH3SnxPb1–xI3 compounds promise a substantial enhancement of both short circuit photocurrent and power conversion efficiency in single junction solar cells. Moreover, we propose a novel tandem architecture design in which both top and bottom cells are made of perovskite absorbers. Our calculations indicate that such perovskite-on-perovskite tandem devices could reach efficiencies over 35%. Our analysis serves to establish the first roadmap for this type of cells based on actual optical characterization data. We foresee that this study will encourage the research on novel near-infrared perovskite materials for photovoltaic applications, which may have implications in the rapidly emerging field of tandem devices.Unión Europea Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 307081 (POLIGHT)España, Ministerio de Economía y Competitividad AT2014-54852- R

Highly efficient perovskite solar cells with tunable structural color

The performance of perovskite solar cells has been progressing over the past few years and efficiency is likely to continue to increase. However, a negative aspect for the integration of perovskite solar cells in the built environment is that the color gamut available in these materials is very limited and does not cover the green-to-blue region of the visible spectrum, which has been a big selling point for organic photovoltaics. Here, we integrate a porous photonic crystal (PC) scaffold within the photoactive layer of an opaque perovskite solar cell following a bottom-up approach employing inexpensive and scalable liquid processing techniques. The photovoltaic devices presented herein show high efficiency with tunable color across the visible spectrum. This now imbues the perovskite solar cells with highly desirable properties for cladding in the built environment and encourages design of sustainable colorful buildings and iridescent electric vehicles as future power generation sources.European Union FP7/ 2007-2013Ministerio de Economía y Competitividad MAT2011-23593Junta de Andalucía FQM524

Electron injection and scaffold effects in perovskite solar cells

In spite of the impressive efficiencies reported for perovskite solar cells (PSCs), key aspects of their working principles, such as electron injection at the contacts or the suitability of the utilization of a specific scaffold layer, are not yet fully understood. Increasingly complex scaffolds attained by the sequential deposition of TiO2 and SiO2 mesoporous layers onto transparent conducting substrates are used to perform a systematic characterization of both the injection process at the electron selective contact and the scaffold effect in PSCs. By forcing multiple electron injection processes at a controlled sequence of perovskite–TiO2 interfaces before extraction, interfacial injection effects are magnified and hence characterized in detail. An anomalous injection behavior is observed, the fingerprint of which is the presence of significant inductive loops in the impedance spectra with a magnitude that correlates with the number of interfaces in the scaffold. Analysis of the resistive and capacitive behavior of the impedance spectra indicates that the scaffolds could hinder ion migration, with positive consequences such as lowering the recombination rate and implications for the current–potential curve hysteresis. Our results suggest that an appropriate balance between these advantageous effects and the unavoidable charge transport resistive losses introduced by the scaffolds will help in the optimization of PSC performance.Unión Europea 7PM / 2007-2013Unión Europea ERC 307081 (POLIGHT)Ministerio de Economía y Competitividad de España MAT2014-54852-RMinisterio de Economía y Competitividad de España MAT2015-70611-ER