Alberto Jiménez-Solano

Plasmonic Nanoparticles as Light-Harvesting Enhancers in Perovskite Solar Cells: A User’s Guide

In this Perspective we discuss the implications of employing metal particles of different shape, size, and composition as absorption enhancers in methylammonium lead iodide perovskite solar cells, with the aim of establishing some guidelines for the future development of plasmonic resonance-based photovoltaic devices. Hybrid perovskites present an extraordinarily high absorption coefficient which, as we show here, makes it difficult to extrapolate concepts and designs that are applied to other solution-processed photovoltaic materials. In addition, the variability of the optical constants attained from perovskite films of seemingly similar composition further complicates the analysis. We demonstrate that, by means of rigorous design, it is possible to provide a realistic prediction of the magnitude of the absorption enhancement that can be reached for perovskite films embedding metal particles. On the basis of this, we foresee that localized surface plasmon effects will provide a means to attain highly efficient perovskite solar cells using films that are thinner than those usually employed, hence facilitating collection of photocarriers and significantly reducing the amount of potentially toxic lead present in the device.

Fine Tuning the Emission Properties of Nanoemitters in Multilayered Structures by Deterministic Control of their Local Photonic Environment

Deterministic control on the dynamics of organic nanoemitters is achieved through precise control of its photonic environment. Resonators are fabricated by a combination of spin- and dip-coating techniques, which allows placement of the emitters at different positions within the sample, thus acting as a probe of the local density of states.

Integration of gold nanoparticles in optical resonators.

The optical absorption of one-dimensional photonic crystal based resonators containing different types of gold nanoparticles is controllably modified by means of the interplay between planar optical cavity modes and localized surface plasmons. Spin-casting of metal oxide nanoparticle suspensions was used to build multilayered photonic structures that host (silica-coated) gold nanorods and spheres. Strong reinforcement and depletion of the absorptance was observed at designed wavelength ranges, thus proving that our method provides a reliable means to modify the optical absorption originated at plasmonic resonances of particles of arbitrary shape and within a wide range of sizes. These observations are discussed on the basis of calculations of the spatial and spectral dependence of the optical field intensity within the multilayers.

Flexible Distributed Bragg Reflectors from Nanocolumnar Templates.

Technological evolution of flexible optoelectronic devices, such as solar cells or light emitting diodes,[1–6] must be accompanied by that of flexible optical and electronic materials in order to fulfill the increasing requirements of higher performance and functionality. In that regard, last years have seen a boost of the research in this field, a wide variety of approaches having been taken to prepare flexible components.[7–11] Integration into devices will require stability of their properties upon bending and stretching, adaptability to different types of substrates, durability, etc.[12] Among optical materials employed in optoelectronics, distributed Bragg reflectors (DBRs) play a central role as either photon frequency filters, optical cavities to enhance spontaneous or stimulated emission[13] or simply as mirrors to increase the time of residence of photons in absorbing electrodes and thus improve their photovoltaic performance.[14–16] In order to attain the flexible version of the classical stratified multilayer structure characteristic of DBRs, a common strategy is to stack thin polymer layers of alternate refractive index.[17] Enhanced spontaneous emission has been observed from flexible optical cavities prepared based on this approach.[18] Also, by rolling two polymers around a cylindrical core, tunable elastic optical multilayered fibers have been attained.[19] However, elastomers usually possess low refractive indexes, typically comprised in a narrow range, so a small dielectric contrast is typically achieved. This means that a large number of layers must be stuck in order to reach intense reflections and only in narrow spectral ranges. One way to increase the refractive index contrast between layers relies on the deposition of hybrid precursors made of a mixture of polymers and higher refractive index inorganic particles.[20] In this way, the refractive index contrast is increased, although its value is limited by the amount of particles that can be dispersed in the polymers. In addition, this approach requires a high degree of physicochemical compatibility of the particle surface with the polymer, or the strict control of the particle formation in a polymeric medium.[21]

Absorption and Emission of Light in Optoelectronic Nanomaterials: The Role of the Local Optical Environment

Tailoring the interaction of electromagnetic radiation with matter is central to the development of optoelectronic devices. This becomes particularly relevant for a new generation of devices offering the possibility of solution processing with competitive efficiencies as well as new functionalities. These devices, containing novel materials such as inorganic colloidal quantum dots or hybrid organic-inorganic lead halide perovskites, commonly demand thin (tens of nanometers) active layers in order to perform optimally and thus maximizing the way electromagnetic radiation interacts with these layers is essential. In this Perspective, we discuss the relevance of tailoring the optical environment of the active layer in an optoelectronic device and illustrate it with two real-world systems comprising photovoltaic cells and light emitting devices.

Full solution process approach for deterministic control of light emission at the nanoscale(Conference Presentation)

Porous nanostructured photonic materials in the shape of periodic multilayers have demonstrated their potential in different fields ranging from photovoltaics[1] to sensing,[2] representing an ideal platform for flexible devices. When applications dealing with light absorption or emission are considered, knowledge on how the local density of states (LDOS) is distributed within them is mandatory[3] in order to realize a judicious design which maximizes light matter interaction. Using a combination of spin and dip-casting we report a detail study of how dye doped polystyrene nanospheres constitute an effective LDOS probe to study its distribution within nanostructured photonic media.[4] This full solution process approach allows to cover large areas keeping the photonics properties. Nanospheres with a diameter of 25 nm are incorporated in nanostructured multilayers (Fig. 1a).. This allows to place them at several positions of the structured sample (Fig. 1b). A combined use of photoluminescence spectroscopy and time resolved measurements are used to optically characterize the samples. While the former shows how depending on the probe position its PL intensity can be enhanced or suppressed, the latter allows to probe the LDOS changes within the sample, monitored via changes in its lifetime. We demonstrate how information on the local photonic environment can be retrieved with a spatial resolution of 25 nm (provided by the probe size) and relative changes in the decay rates as small as ca. 1% (Fig. 1c), evidencing the possibility of exerting a fine deterministic control on the photonic surroundings of an emitter. References [1] C. López-López, S. Colodrero, M. E. Calvo and H. Míguez, Energy Environ. Sci., 23, 2805 (2013). [2] A. Jiménez-Solano, C. López-López, O. Sánchez-Sobrado, J. M. Luque, M. E. Calvo, C. Fernández-López, A. Sánchez-Iglesias, L. M. Liz-Marzán and H. Míguez. Langmuir, 28, 9161 (2012). [3] N. Danz, R. Waldhäusl, A. Bräuer and R. Kowarschik, J. Opt. Soc. Am. B, 19, 412 (2010). [4] A. Jiménez-Solano, J. F. Galisteo-López and H. Míguez, Small, 11, 2727 (2015).

Optimized light harvesting and charge collection properties of plastic dye-sensitized solar cells with theoretical modeling and synergistic approach

Highly efficient dye-sensitized solar cells were prepared on plastic substrates by a synergistic approach and reached an efficiency of 8.6%, which optimized the light trapping and charge collection properties based on a theoretical modeling.