The solar‐to‐electric power‐conversion efficiency (η) of dye‐sensitized solar cells can be greatly enhanced by integrating a mesoporous, nanoparticle‐based, 1D photonic crystal as a coherent scattering layer in the device. The photogenerated current is greatly improved without altering the open‐circuit voltage of the cell, while keeping the transparency of the cell intact. Improved average η values between 15% and 30% are attained.
Herein we present a fast, reliable method for building nanoparticle-based 1D photonic crystals in which a periodic modulation of the refractive index is built by alternating different types of nanoparticles and by controlling the level of porosity of each layer. The versatility of the method is further confirmed by building up optically doped photonic crystals in which the opening of transmission windows due to the creation of defect states in the gap is demonstrated. The potential of this new type of structure as a sensing material is illustrated by analyzing the specific color changes induced by the infiltration of solvents of different refractive indexes.
The vapor sorption properties of multilayers made of ordered mesoporous thin films with tailored composition and mesostructure are herein investigated. Optical reflectance measurements versus partial pressure of several vapors are performed to analyze the interplay between the affinity to and the accessibility of the different types of layers in the structure. We find that the behavior of a mesoporous oxide layer within the multilayer largely differs from that of the isolated thin film, its sorption properties being determined by the interaction with neighboring films. An explanation of the phenomena observed in these complex systems is provided in terms of the pore size, the affinity of each type of layer to specific compounds, and the effect of neighboring layers in the sorption properties of bilayers by an independent environmental ellipsometric study.
Herein we report an analysis of the variation of the optical properties of different nanoparticle-based one-dimensional photonic crystal architectures versus changes in the ambient vapor pressure. Gradual shift of the optical response provides us with information on the sorption properties of these structures and allow us to measure precise adsorption isotherms of these porous multilayers. The potential of nanoparticle-based one-dimensional photonic crystals as base materials for optical sensing devices is demonstrated in this way.
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.
A synthetic route to building photoconducting films of TiO2 nanoparticles that display bright structural color is presented. The color arises as a result of the periodic modulation of the refractive index, which is achieved by controlling the degree of porosity of each alternate layer through the particle size distribution of the precursor suspensions. The suspensions are cast in the shape of a film by spin‐coating, which allows tailoring of the lattice parameter of the periodic multilayer, thus tuning the Bragg peak spectral position (i.e., its color) over the entire visible region. Photoelectrochemical measurements show that the Bragg mirrors are conductive and distort the photocurrent response as a result of the interplay between photon and electron transport.
A working electrode design based on a highly porous 1D photonic crystal structure that opens the path towards high photocurrents in thin, transparent, dye‐sensitized solar cells is presented. By enlarging the average pore size with respect to previous photonic crystal designs, the new working electrode not only increases the device photocurrent, as predicted by theoretical models, but also allows the observation of an unprecedented boost of the cell photovoltage, which can be attributed to structural modifications caused during the integration of the photonic crystal. These synergic effects yield conversion efficiencies of around 3.5% by using just 2 μm thick electrodes, with enhancements between 100% and 150% with respect to reference cells of the same thickness.
A simple analytical model that allows designing one-dimensional photonic crystal based dye sensitized solar cells of optimized performance, accounting for the actual optical features of the device, is herein presented. Based on the theoretical description of the effect of coupling such Bragg mirrors to the light harvesting electrode, recently reported experimental values of the spectral dependence of incident photon to current conversion efficiency attained for such structures are fairly reproduced and rationalized. A thorough analysis of them in terms of the interplay between the effect of the electrode thickness and the characteristics of the Bragg reflection, such as intensity, spectral position, and width, is provided. Predictions on the maximum enhancement factors expected for realistic structures are also presented.
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