Plasmon resonances in metal nanostructures have been extensively harnessed for light trapping in mesoporous solar cells (MSCs), including dye-sensitized solar cells (DSSCs) and recently in perovskite solar cells (PSCs). By altering the geometry, dimension, and composition of metal nanostructures, their optical characteristics can be tuned to either overlap with the sensitizer absorption and enhance light harvesting, or absorb light at a wavelength complementary to the sensitizer enabling broadband solar light capture in MSCs. In this comprehensive review, we discuss the mechanisms of plasmonic enhancement in MSCs including far-field coupling of scattered light, near-field coupling of localized electromagnetic fields, hot electron transfer, and plasmon resonant energy transfer. We then summarize the progress in plasmon enhanced DSSCs in the past decade and decouple the impact of metal nanostructure shape, size, composition, and surface coatings on the overall efficiency. Further, we also discuss the recent advances in plasmon-enhanced perovskite solar cells. Distinct from other published reviews, we discuss the significance of femtosecond spectroscopies to probe the fundamental underpinnings of plasmon enhanced phenomena and understand the mechanisms that give rise to energy transfer between metal nanoparticles and solar materials. The review concludes with a discussion on the challenges in plasmonic device fabrication, and the promise of low-loss semiconductor nanocrystals for plasmonic enhancement in MSCs that facilitate light capture in the infrared. Broader contextEmerging photovoltaics, including PSCs and their predecessors, DSSCs, collectively described as mesoporous solar cells (MSCs), have rapidly evolved as a serious contender to traditional crystalline silicon photovoltaics due to the inexpensive materials and low processing costs. However low efficiencies, specifically in thin-film architectures, have remained a major hurdle to commercialization in these classes of MSCs. The past decade has witnessed significant improvements in device performance of MSCs by integrating subwavelength plasmonic nanostructures in the active layer. Metal nanostructures function as a secondary light source to augment the total light trapped within the mesoporous layer, enabling enhanced carrier generation. This consequently decreases the amount of active material required to achieve high efficiency solar conversion. Plasmon-enhanced thin-film MSCs will ultimately enable integration on flexible substrates, resulting in low-cost and high efficiency flexible solar cells compatible with scalable manufacturing routes such as inkjet printing and roll-to-roll processing. By understanding the fundamental mechanisms of plasmonic enhancement in MSCs, this technology will ultimately enable rapid advancements in the active light management of a range of optoelectronic devices including photovoltaics, sensors, photoelectrochemical cells, and photodetectors. Absorption of TiO 2 electrodes with Au@Ag nanoparticles incorporated. (c) Current...

Plasmon resonances of anisotropic multibranched nanostructures are governed by their geometry, allowing morphology-directed selective manipulation of the optical properties. In this work, we have synthesized multibranched gold nanoantennas (MGNs) of variable geometry by a one-step seedless approach using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as a capping and reducing agent. This approach enables us to modulate the MGNs' geometry by controlling three different parameters: concentration of HEPES, concentration of Au 3+ , and pH of HEPES buffer. By altering the MGNs morphology with minimal increase in the overall dimensions, the plasmon resonances were tuned from the visible to the near-infrared. The MGNs plasmon resonances demonstrated a nonintuitive blue-shift when pH > pK a of HEPES which we attributed to emergence of charge transfer oscillations formed when MGNs cluster to dimers and trimers. Further, due to the presence of multiple sharp protrusions, the MGNs demonstrated a refractive index sensitivity of 373 nm/RIU, which is relatively high for this class of branched nanostructures of similar size. Finally, the sharp protrusions of MGNs also give rise to intense photothermal efficiencies; ∼53 °C was achieved within 5 min of laser illumination, demonstrating the efficacy of MGNs in therapeutic applications. By modulating the mass density of MGNs, the laser flux, and time of illumination, we provide a detailed analysis of the photothermal characteristics of MGNs.

This review gives a comprehensive overview of recent progress made in mixed-halide hybrid perovskite materials, focusing in particular on the impact of halide substitution on optoelectronic properties and trends in carrier dynamics.