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.

Hybrid organic-inorganic perovskite materials have risen up as leading components for light-harvesting applications. However, to date many questions are still open concerning the operation of perovskite solar cells (PSCs). A systematic analysis of the interplay among structural features, optoelectronic performance, and ionic movement behavior for FA0.83 MA0.17 Pb(I0.83 Br0.17 )3 PSCs is presented, which yield high power conversion efficiencies up to 20.8%.

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.

Herein we present a combined study of the evolution of both the photoluminescence (PL) and the surface chemical structure of organic metal halide perovskites as the environmental oxygen pressure rises from ultrahigh vacuum up to a few thousandths of an atmosphere. Analyzing the changes occurring at the semiconductor surface upon photoexcitation under a controlled oxygen atmosphere in an X-ray photoelectron spectroscopy (XPS) chamber, we can rationalize the rich variety of photophysical phenomena observed and provide a plausible explanation for light-induced ion migration, one of the most conspicuous and debated concomitant effects detected during photoexcitation. We find direct evidence of the formation of a superficial layer of negatively charged oxygen species capable of repelling the halide anions away from the surface and toward the bulk. The reported PL transient dynamics, the partial recovery of the initial state when photoexcitation stops, and the eventual degradation after intense exposure times can thus be rationalized.

Perovskite solar cells carry the banner for emerging photovoltaics since they have demonstrated power conversion efficiency values well above 20%, which were traditionally only accessible for fairly established technologies such as silicon. Indeed, ABX 3 perovskite materials have revolutionized solar cells due to their ease of processing and outstanding electronic and optical properties, which make them ideal candidates for the development of multi-junction devices aiming to surpass limits associated to stand-alone technologies. In this review we discuss the latest regarding this matter. First, we introduce standard materials and processing techniques involved in the preparation of state-of-the-art perovskite solar cells. We then discuss the development of perovskite-based tandem devices in which ABX 3 perovskite acts as the active material in the top subcell and Si, CIGS, polymer, or ABX 3 act as bottom subcells. Finally, we provide the reader with a discussion on the different lines of research that this rapidly developing field may follow.

Mesoporous titania thin films with accessible porosity and anatase structure were synthesized on conductive glass or silicon substrates. Ti K-edge XANES was used to assess Ti local coordination. Analysis of the pre-edge region permitted accurate quantification of the degree of crystalline nature of the inorganic walls upon thermal treatment. The substrate has a marked effect:  film crystallization takes places at temperatures 100 °C lower in the crystalline Si, with respect to conductive glass. Accordingly, remarkable photocatalytic properties are found in well-crystallized mesoporous titania deposited onto conductive silicon.

Herein we present an experimental study of the spectral dependence of the photogenerated current of opal-based solar cells. We analyze the incident photon-to-current conversion efficiency (IPCE) for dye-sensitized solar cells in which colloidal crystals are introduced in different configurations. We prove that a dye-sensitized nanocrystalline titanium oxide electrode moulded in the shape of an inverse opal shows a decrease of efficiency for the spectral region in which a photonic stop band opens up. Contrarily, when a standard thin film of disordered titania nanocrystallites is coupled to an inverse opal, the mirror effect of the photonic crystal at band gap frequencies increases the light harvesting efficiency of the cell and thus the IPCE. This effect is further demonstrated by coupling an inverse opal multilayer to a homogeneous electrode, with two well-defined spectral ranges of increased photogenerated current being detected.

In recent times, several synthetic pathways have been developed to create multilayered materials of diverse composition that combine accessible porosity and optical properties of structural origin, i.e., not related to absorption. These materials possess a refractive index that varies periodically along one direction, which gives rise to optical diffraction effects characteristic of Bragg stacks or onedimensional photonic crystals (1DPCs). The technological potential of such porous optical materials has been demonstrated in various fields related to energy and environmental sciences, such as detection and recognition of targeted biological or chemical species, photovoltaics, or radiation shielding. In all cases, improved performance is achieved as a result of the added functionality porosity brings. In this review, a unified picture of this emerging field is provided.