Multi-Shaped Ag Nanoparticles in the Plasmonic Layer of Dye-Sensitized Solar Cells for Increased Power Conversion Efficiency

Optoelectronic Enhancement of Perovskite Solar Cells through the Incorporation of Plasmonic Particles

The optoelectronic advantages of anchoring plasmonic silver and copper particles and non-plasmonic titanium particles onto zinc oxide (ZnO) nanoflower (NF) scaffolds for the fabrication of perovskite solar cells (PSCs) are addressed in this article. The metallic particles were sputter-deposited as a function of sputtering time to vary their size on solution-grown ZnO NFs on which methylammonium lead iodide perovskite was crystallized in a controlled environment. Optical absorption measurements showed impressive improvements in the light-harvesting efficiency (LHE) of the devices using silver nanoparticles and some concentrations of copper, whereas the LHE was relatively lower in devices used titanium than in a control device without any metallic particles. Fully functional PSCs were fabricated using the plasmonic and non-plasmonic metallic film-decorated ZnO NFs. Several fold enhancements in photoconversion efficiency were achieved in the silver-containing devices compared with the control device, which was accompanied by an increase in the photocurrent density, photovoltage, and fill factor. To understand the plasmonic effects in the photoanode, the LHE, photo-current density, photovoltage, photoluminescence, incident photon-to-current conversion efficiency, and electrochemical impedance properties were thoroughly investigated. This research showcases the efficacy of the addition of plasmonic particles onto photo anodes, which leads to improved light scattering, better charge separation, and reduced electron–hole recombination rate.

Effect of Au Nanoparticles and Scattering Layer in Dye-Sensitized Solar Cells Based on Freestanding TiO2 Nanotube Arrays

The development of high efficiency dye-sensitized solar cells (DSSCs) has received tremendous attention. Many researchers have introduced new materials for use in DSSCs to achieve high efficiency. In this study, the change in power conversion efficiency (PCE) of DSSCs was investigated by introducing two types of materials—Au nanoparticles (Au NPs) and a scattering layer. A DSSC fabricated without neither Au NPs nor a scattering layer achieved a PCE of 5.85%. The PCE of a DSSC based on freestanding TiO₂ nanotube arrays (f-TNTAs) with Au NPs was 6.50% due to better electron generation because the plasmonic absorption band of Au NPs is 530 nm, which matches the dye absorbance. Thus, more electrons were generated at 530 nm, which affected the PCE of the DSSC. The PCE of DSSCs based on f-TNTAs with a scattering layer was 6.61% due to better light harvesting by scattering. The scattering layer reflects all wavelengths of light that improve the light harvesting in the active layer in DSSCs. Finally, the PCE of DSSCs based on the f-TNTAs with Au NPs and a scattering layer was 7.12% due to the synergy of better electron generation and light harvesting by plasmonics and scattering. The application of Au NPs and a scattering layer is a promising research area for DSSCs as they can increase the electron generation and light harvesting ability.

Biomimetic ZnO for Dye-Sensitized Solar Cells

A research study on the application of biomimetic ZnO (from eggshell membranes) as photoanodes in dye-sensitized solar cells (DSSCs) is presented. Biomimetic ZnO powder was produced and characterized. Its surface area, crystallinity, and morphology were analyzed and compared to commercial ZnO. Then, solar cells with and without dye were assembled using both the biomimetic and commercial oxides. On the dye-less cell, the oxide assumes the role of the photon absorber, while in the dye-sensitized cells, the oxide’s major function is the separation of the electron-hole pair and conduction of the electric charges formed. The characterization of the oxides showed that the biomimetic synthesis produced ZnO with a larger surface area, smaller crystallite size, and larger light absorption, possibly due to crystalline defects. SEM analysis on biomimetic ZnO revealed a tubular microstructure formed by nanocrystals, instead of the commercial powder showing spherical particles.

Plasmonic enhancement of betanin-lawsone co-sensitized solar cells via tailored bimodal size distribution of silver nanoparticles

Natural pigment-based photosensitizers are an attractive pathway for realizing low cost and environmentally friendly solar cells. Here, broadband light-harvesting is achieved using two natural pigments, betanin and lawsone, absorbing in the green and blue region of the solar spectrum respectively. The use of bimodal size distribution of AgNPs tailored for each of the pigments to further increase their efficiency is the key feature of this work. This study demonstrates a significant enhancement in current-density, voltage, and efficiency by 20.1%, 5.5%, and 28.6% respectively, in a betanin-lawsone co-sensitized solar cell, via plasmonic enhancement using silver nanoparticles (AgNPs). The optimum sizes of the nanoparticles have been calculated by studying their optical response and electric field profiles using Finite Difference Time Domain (FDTD) simulations, aimed at matching their resonant wavelengths with the absorption bands of the dyes. Simulations show that AgNPs of diameters 20 nm and 60 nm are optimum for enhanced absorption by lawsone and betanin respectively. The FDTD simulations of the plasmonic photoelectrodes demonstrated 30% and 15% enhancement in the power absorption by betanin and lawsone at the LSPR peaks of the 60 nm and 20 nm AgNPs respectively. An optimum overall concentration of 2% (v/v) and a ratio of 4:1 (20 nm:60 nm) of the bimodal distribution of the AgNPs, was determined for incorporation in the photoanodes. An average efficiency of 1.02 ± 0.006% was achieved by the betanin-lawsone co-sensitized solar cell with the bimodal distribution of AgNPs, compared to 0.793 ± 0.006% achieved by the non-plasmonic solar cell of otherwise identical configuration. Electrochemical impedance spectroscopy confirmed that the incorporation of the bimodal distribution of AgNPs in the solar cells also enabled enhanced electron lifetime and reduced recombination compared to the non-plasmonic counterpart, thereby improving the charge transfer. The plasmonic enhancement methodology presented here can be applied to further improve the efficiency of other natural dye-sensitized solar cells.

Au-Nanoparticle-Embedded Open-Ended Freestanding TiO2 Nanotube Arrays in Dye-Sensitized Solar Cells for Better Electron Generation and Electron Transport

Freestanding TiO₂ nanotube arrays (TNTAs) were prepared by an electrochemical method, and dye-sensitized solar cells (DSSCs) were fabricated with the open-ended freestanding TNTAs incorporated with Au nanoparticles (NPs). Open-ended freestanding TNTAs were prepared by etching the barrier layer of closed-ended freestanding TNTAs using an ion milling method, and Au NPs were incorporated into the channel of the open-ended freestanding TNTAs by an electrodeposition method. The Au-NP-embedded open-ended freestanding TNTAs were applied to DSSCs to improve the energy conversion efficiency (ECE) by better electron generation and electron transport. The ECE of DSSCs based on the closed-ended freestanding TNTAs with Au NPs increased to 6.116% from 5.502% for DSSCs based on the closed-ended freestanding TNTAs without Au NPs, an enhancement of 11.16% because of better electron generation by the plasmonic and charging effects of the Au NPs. However, the ECE of DSSCs based on the closed-ended freestanding TNTAs incorporated with Au NPs for 40 s decreased from 6.116 to 5.336% because aggregation of the Au NPs led to a decrease in the open-circuit voltage (V _oc) and fill factor. For enhanced ECE of DSSCs, the barrier layer of closed-ended freestanding TNTAs was etched by an ion milling method for 0, 30, 60, or 90 min to provide "open-ended freestanding TNTAs". Then, Au NPs were incorporated into the open-ended freestanding TNTAs. After the barrier layer was completely removed by the ion milling method for 90 min, the ECE of the DSSCs reached 7.120% because the electron transport and electrolyte diffusion were improved by the elimination of the barrier layer of the freestanding TNTAs.

Au-Embedded and Carbon-Doped Freestanding TiO2 Nanotube Arrays in Dye-Sensitized Solar Cells for Better Energy Conversion Efficiency

Dye-sensitized solar cells (DSSCs) are fabricated with freestanding TiO2 nanotube arrays (TNTAs) which are incorporated with Au nanoparticles (NPs) and carbon materials via electrodeposition and chemical vapor deposition (CVD) method to create a plasmonic effect and better electron transport that will enhance their energy conversion efficiency (ECE). The ECE of DSSCs based on the freestanding TNTAs is 5.87%. The ECE of DSSCs, based on the freestanding TNTAs with Au NPs or carbon materials, is 6.57% or 6.59%, respectively, and the final results of DSSCs according to the freestanding TNTAs with Au NPs and carbon materials is increased from 5.87% to 7.24%, which is an enhancement of 23.34% owing to plasmonic effect and better electron transport. Au NPs are incorporated into the channel of freestanding TNTAs and are characterized by CS-corrected-field emission transmission electron microscope (Cs-FE-TEM) and elemental mapping. Carbon materials are also well-incorporated in the channel of freestanding TNTAs and are analyzed by Raman spectroscopy.

On Modeling of Plasmon-Induced Enhancement of the Efficiency of Solar Cells Modified by Metallic Nano-Particles

We demonstrate that the direct application of numerical packets like Comsol to plasmonic effect in solar cells metallically modified in nano-scale may be strongly inaccurate if quantum corrections are neglected. The near-field coupling of surface plasmons in metallic nanoparticles deposited on the top of a solar cell with band electrons in a semiconductor substrate strongly enhances the damping of plasmons in metallic components, which is not accounted for in standard numerical packets using the Drude type dielectric function for metal (taken from measurements in bulk or in thin layers) as the prerequisite for the numerical e-m field calculus. Inclusion of the proper corrections to plasmon damping causes additional enhancement of the plasmon-induced photo-effect efficiency growth of a metalized photo-diode by ten percent, at least, in comparison to only effect induced by the electric field concentration near metallic nanoparticles. This happens to be consistent with the experimental observations which cannot be explained by only local increases of the electrical field near the curvature of metallic nanoparticles determined by a finite-element solution of the Maxwell⁻Fresnel boundary problem as given by a numerical system like Comsol. The proper damping rate for plasmons can be identified by application of the Fermi Golden Rule approach to the plasmon-band electron coupling. We demonstrate this effect including the material and size dependence in two types of solar cells, multi-crystalline Si and CIGS (copper-indium-gallium-diselenide) as idealized photo-diode semiconductor substrate modified by various metallic nano-particles, in comparison to the experimental data and Comsol simulation.

Nanoarchitectures in dye-sensitized solar cells: metal oxides, oxide perovskites and carbon-based materials

Dye-sensitized solar cells (DSSCs) have aroused great interest and been regarded as a potential renewable energy resource among the third-generation solar cell technologies to fulfill the 21^st century global energy demand. DSSCs have notable advantages such as low cost, easy fabrication process and being eco-friendly in nature. The progress of DSSCs over the last 20 years has been nearly constant due to some limitations, like poor long-term stability, narrow absorption spectrum, charge carrier transportation and collection losses and poor charge transfer mechanism for regeneration of dye molecules. The main challenge for the scientific community is to improve the performance of DSSCs by using different approaches, like finding new electrode materials with suitable nanoarchitectures, dyes in composition with promising semiconductors and metal quantum dot fluorescent dyes, and cost-effective hole transporting materials (HTMs). This review focuses on DSSC photo-physics, which includes charge separation, effective transportation, collection and recombination processes. Different nanostructured materials, including metal oxides, oxide perovskites and carbon-based composites, have been studied for photoanodes, and counter electrodes, which are crucial to achieve DSSC devices with higher efficiency and better stability.