ChemInform Abstract: Nanomaterials for Energy Conversion and Storage

Using metal-dielectric core-shell nanoparticles to tune the plasmonic resonance peak for increasing optical absorption in solar cells is proposed and investigated. The enhancement region could be tuned in a large wavelength range of about 200nm.

In developing photovoltaic devices with high efficiencies, quantitative determination of the carrier loss is crucial. In conventional solar-cell characterization techniques, however, photocurrent reduction originating from parasitic light absorption and carrier recombination within the light absorber cannot be assessed easily. Here, we develop a general analysis scheme in which the optical and recombination losses in submicron-textured solar cells are evaluated systematically from external quantum efficiency (EQE) spectra. In this method, the optical absorption in solar cells is first deduced by imposing the anti-reflection condition in the calculation of the absorptance spectrum, and the carrier extraction from the light absorber layer is then modeled by considering a carrier collection length from the absorber interface. Our analysis method is appropriate for a wide variety of photovoltaic devices, including kesterite solar cells [Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4], zincblende CdTe solar cells, and hybrid perovskite (CH3NH3PbI3) solar cells, and provides excellent fitting to numerous EQE spectra reported earlier. Based on the results obtained from our EQE analyses, we discuss the effects of parasitic absorption and carrier recombination in different types of solar cells.

Front-surface photonic nanostructures contribute both reduced reflection loss and light trapping to increase optical absorption in solar cells. We investigated the effect of sub-wavelength photonic nanostructures on light trapping in thin-film crystalline silicon solar cells. We clarified that, even though the angle distribution of scattered light is small compared with that in the case of Lambertian scattering, light trapping enhances with increasing depth of the surface photonic nanostructure, which originates from the direction-dependent light transmission in the surface photonic nanostructure. Our findings indicate that this direction-dependent light transmission contributes to the advanced photon management in thin-film solar cells.

The effort to improve the energy conversion efficiency of polymer solar cells has led to the design of novel donor polymers. To improve open circuit photovoltages (OCVs) and the spectral coverage of the solar spectrum, researchers have looked for materials with high HOMO values, an easily modified electronic structure, and sufficient electronic transport within the polymers. One advance in design from our laboratories has been the development of a class of alternating polyfluorene copolymers (APFOs), which can be combined with fullerenes to make bulk heterojunction materials for photovoltaic conversion. This Account describes copolymers of fluorene that we designed to expand the range the optical absorption of solar cells to include wavelengths out to 1000 nm. In most cases, we combine these polymers with acceptors from the fullerene family, typically the phenyl C(61) butyric acid methyl ester (PCBM) molecule, to generate solar cell materials. The synthesis of alternating copolymers of fluorene with various donor-acceptor-donor elements provides the opportunity to shift both HOMO and LUMO, which we have followed by electrochemical spectroscopy. Moving the LUMO of the APFOs farther from the vacuum level eventually leads to a situation where the driving force for photo-induced charge transfer from polymer donor to fullerene acceptor goes to zero, resulting in inefficient charge generation. Moving the HOMO level closer to the vacuum level reduces the OCV of devices made from bulk heterojunction blends. As we move the bandgap toward lower energies and increase the overlap of optical absorption with the solar spectrum, both these events eventually occur. In devices based on these APFO/fullerene blends, the performance depends on the OCV, the photocurrent under solar illumination, and the fill factor. The fill factor is influenced by electrical transport and charge generation. Optimizing these parameters requires new solutions to the perennial conflict between optically thin devices, where electrical extraction of charge is not a limitation, and the optically thick devices, where extraction of charge is hampered by trapping and recombination. As a result, we have developed methods to trap light in optically thin devices. When the thin film flexible solar cells are folded, multiple reflection between adjacent solar cells leads to a longer path length for the photon through the devices and considerable improvement of the optical dissipation in the active material. These optical tricks also enable an alternative route to tandem devices, where two different bandgap materials are located on adjacent folds. Thus light not absorbed in one cell is reflected onto the next cell to produce an effective optical series arrangement. Using experiments and simulations of the light trapping effects, we demonstrate power conversion efficiency enhancements of up to a factor of 1.8.

Keywords: atomic layer deposition; batteries; energy conversion; electrochemistry; electrolysis; fuel cells; photovoltaics; solar cells; thin films

Efficient energy storage systems represent a critical technology across many sectors including consumer electronics, electrified transportation, and a smart grid accommodating intermittent renewable energy sources. Arguably, the most important advance in energy storage over the past three decades is the lithium-ion battery, which was recently recognized with the Nobel Prize in Chemistry. However, despite its many successes, issues related to safety, energy density, charging time, and operating temperature range have hindered the realization of the full potential of lithium-ion battery technology, particularly in large-scale applications such as grid-level storage and full electrification of transportation networks. Nanostructured materials were once thought to present compelling opportunities for next-generation lithium-ion batteries, but inherent problems related to high surface area to volume ratios at the nanometer-scale (e.g., undesirable surface chemical interactions between electrodes and electrolytes) have impeded their adoption for commercial applications. This talk will explore how the chemical inertness of select two-dimensional (2D) materials are driving a resurgence in nanostructured lithium-ion battery materials [1]. For example, conformal graphene coatings on lithium-ion battery cathode powders mitigate surface degradation and minimize the formation of the solid electrolyte interphase, thus improving cycling stability [2]. In addition, the high electrical conductivity of graphene reduces cell impedance, resulting in enhanced kinetics that enable high-rate capability and low-temperature performance down to –20 °C [3]. On the other hand, ionogel electrolytes based on ionic liquids and hexagonal boron nitride (hBN) nanoplatelets provide safe, high-rate operation at high temperatures up to 175 °C, which represents the highest operating temperature to date for solid-state lithium-ion batteries [4,5]. The strong interfacial interactions between hBN and ionic liquids further enable novel electrolyte architectures based on layered heterostructure ionogels that result in unprecedently high energy densities and rate performance for solid-state batteries [6].[1] H. Bergeron, et al., Chemical Reviews, 121, 2713 (2021).[2] K.-Y. Park, et al., Advanced Energy Materials, 10, 2001216 (2020).[3] K.-Y. Park, et al., Advanced Materials, DOI: 10.1002/adma.202106402 (2021).[4] W. J. Hyun, et al., ACS Nano, 13, 9664 (2019).[5] W. J. Hyun, et al., Advanced Energy Materials, 10, 2002135 (2020).[6] W. J. Hyun, et al., Advanced Materials, 33, 2007864 (2021).

In this paper, a graded SiNx and SiOxNy structure is proposed as antireflection coatings deposited on top of amorphous silicon (α-Si) thin-film solar cell. The structural parameters are optimized by differential evolution in order to enhance the optical absorption of solar cells to the greatest degree. The optimal design result demonstrates that the nonlinear profile of dielectric constant is superior to the linear profile, and discrete multilayer graded antireflection coatings can outperform near continuously graded antireflection coatings. What's more, the electric field intensity distributions clearly demonstrate the proposed graded SiNx and SiOxNy structure can remarkably increase the magnitude of electric field of a-Si:H layer and hence, enhance the light trapping of a-Si:H thin-film solar cells in the whole visible and near-infrared spectrum. Finally, we have compared the optical absorption enhancements of proposed graded SiNx and SiOxNy structure with nanoparticles structure, and demonstrated that it can result in higher enhancements compared to the dielectric SiC and TiO2 nanoparticles. We have shown that the optimal graded SiNx and SiOxNy structure optimized by differential evolution can reach 33.31% enhancement which has exceeded the ideal limit of 32% of nanoparticles structure including plasmonic Ag nanoparticles, dielectric SiC and TiO2 nanoparticles.

Graphitic carbon is extensively used as anode material in most of the commercial lithium-ion batteries due to its low cost and high coulombic efficiency. However, capacity of carbon anode (372mAh/g and 830mAh/mL) is limited by the reversible electrochemical intercalation of lithium ions in its structure. So, alternative research directions and different anode materials are currently being investigated with an aim to achieve high capacity and cycling stability. Recently, nano-material research has shed light on many high performing materials. Among these, metal oxide based materials such as SnO2, MoO2, Co(OH)2 have been recognized as one of the potential candidates for anode material of lithium–ion batteries because of its higher specific lithium storage capacity [1, 2, 3]. But, their poor capacity retention over long-term charge-discharge cycling due to low electrical conductivity has prevented its use as commercial anode material in lithium-ion batteries. Furthermore, during the electrochemical cycling, metal oxides typically break into small metal clusters, resulting in a large volume expansion and a loss of capacity [4]. For improving the performance of metal oxide based materials, nanostructured materials have received much attention as battery electrodes due to the short transport lengths for both electrons and Li ions, higher electrode-electrode contact area, and better accommodation of the strain of Li insertion/extraction [5]. Although there have been reports in the electrochemical behavior and performance improvement on metal oxide based anode materials for lithium ion batteries, it is still difficult to prove the reaction mechanism and abnormal capacity clearly. For accurate explanation of reaction mechanism and abnormal capacity, it is important to analyze each region systematically. Herein, we successfully synthesized nano-structured metal oxide materials through simple synthetic strategy. This research also included its novel reaction mechanism during electrochemical cycling with lithium. Structure and electrochemical properties of synthesized material were studied by diverse electrochemical tests, combination of the synchrotron radiation XRD and XAS techniques. Especially, the changes in the local structures during cycling were investigated systematically on the basis of XAS analysis. Based on these results, novel reaction mechanism about the nano-structured metal oxide based anode material during electrochemical cycling was suggested specifically. This finding will not only be helpful in a more complete understanding of the reaction mechanism of metal oxide based anode materials but also will offer valuable guidance for developing new anode materials with abnormal high capacity for next generation rechargeable batteries. More detailed discussion will be presented at the time of meeting. [1]. Dong, Q et al., Materials Research Bulletin, 2011. 46(8): p. 1156-1162. [2]. I. A. Courtney and J. R. Dahn, J. Electrochem. Soc., 1997, 144, 2045 [3]. Wang, Z. Y et al., Chem. Commun. 2010, 46, 6906−6908 [4]. Poizot, P et al., Nature 2000, 407, 496−499 [5]. Maier, J et al., Nat. Mater. 2005, 4, 805−815.

Na role during sulfurization of NaF/Cu/SnS2 stacked precursor for formation of Cu2SnS3 thin film as absorber of solar cell

Sub-bandgap absorption in polymer-fullerene solar cells studied by temperature-dependent external quantum efficiency and absorption spectroscopy

Metal oxides (MOs) have attracted extensive attention because they possess various applications such as lithium- ion batteries (LIBs), dye sensitized solar cells (DSSCs), fuel cells, catalysis, gas sensors, water splitting and supercapacitors due to low cost and high compatibility with the environment. This paper is a review on recent patents and scientific research literatures related to the synthesis, and energy storage and conversion of MOs in LIBs, DSSCs and supercapacitors. These MOs are mainly transition MOs such as Co3O4, CoO, Fe2O3, Fe3O4, Mn3O4 and MnO2. Some patents and scientific research literatures are also involved in MOs such as Cu2O, TiO2, NiO, SiO2, SnO, ZnO, SnO2, Zn2SnO4-SnO2 and ruthenium oxide. In addition, some problems existing with energy storage and conversion, and future research directions are also addressed. Keywords: Dye sensitized solar cells, energy storage and conversion, lithium-ion batteries, metal oxides, supercapacitors, Nanopowder, Submicron Powder, Photoanodes, fuel cells, gas sensors

Porous silicon (Si) has a tetrahedral structure similar to that of sp3-hybridized carbon atoms in a typical diamond structure, which affords it unique chemical and physical properties including an adjustable intrinsic bandgap, a high-speed carrier transfer efficiency. It has shown great potential in photocatalysis, rechargeable batteries, solar cells, detectors, and electrocatalysis. This review introduces various porous Si-supported electrocatalysts and analyzes the reasons why porous Si is used as a new carrier/active sites from the perspectives of its molecular structure, electronic properties, synthesis methods, etc. The electrochemical applications of porous Si-based electrocatalysts in energy conversion reactions such as hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, and total water decomposition together with lithium-ion battery and supercapacitor in energy storage are summarized. The challenges and future research directions for porous Si are also discussed. This review aims to deepen the understanding of porous Si and promote the development and applications of this new type of Si material.

Energy storage technologies have become increasingly essential in addressing the global transition toward renewable energy systems. The rapid global shift toward renewable energy has made efficient and reliable energy storage technologies (ESTs) essential for addressing the intermittency of solar, wind, and other clean energy sources. Recent research highlights significant advancements in battery chemistries, supercapacitors, hydrogen storage, and thermal energy systems; however, persistent challenges such as high manufacturing costs, limited cycle life, low energy density, and environmental impacts continue to hinder large-scale implementation. Despite the growing number of studies, there is a lack of integrated knowledge that systematically maps recent trends, material innovations, and application specific challenges. This review aims to bridge that gap by comprehensively analyzing advancements in energy storage technologies over the past decade, evaluating key performance indicators such as energy and power density, efficiency, and lifecycle sustainability. By synthesizing findings from peer-reviewed literatures this study identifies critical barriers and emerging strategies such as nanostructured materials, hybrid systems, and circular economy approaches that could redefine future energy storage landscapes. The conclusions underscore the urgent need for interdisciplinary research, material optimization, and cost-effective designs to accelerate the development and deployment of next-generation storage technologies.

Considering the potential advantages of organic solar cells over their inorganic counterpart and the promise of plasmonic nanotechnology, an organic solar cell structure with integrated metal nanostructures is proposed and numerically investigated in this work. Incorporation of metal nanostructures in the active layer of a solar cell is a promising approach, as it can potentially induce localized and propagating plasmonic modes, cavity modes and optical scattering, thereby increasing optical absorption and hence conversion efficiency. In this work, the proposed plasmonic-organic solar cell structure (bulk heterojunction organic active layer with integrated metal nanostructures) is theoretically modeled and its performance parameters are evaluated. The investigation is carried out for nanostructures of different materials (silver and gold) and of different shapes (triangular, hexagonal and circular). The results of the analysis show increase in the values of power conversion efficiency and short-circuit current density of these plasmonically-modified organic solar cells. The overall optical absorption is found to be greatly enhanced for such solar cell structures compared to the basic organic solar cell.

The grand challenge of a sustainable production and use of energy has focused research on the nanostructure of materials. This aspect is considered of critical importance for improving the performance of advanced materials and electrodes to meet demanding expectations. Carbon nanotubes (CNTs) are the first and most-successful example of nanomaterials, and play a central role in the development of advanced solutions for sustainable energy applications. However, notwithstanding the rising scientific and technological interest in CNTs, their use is still largely based on phenomenological observations that miss the complexities of the nanostructure and characteristics of these materials. This Concept paper addresses the need for a rational design of CNTs for energy applications, based on an understanding of the key aspects to be considered for their optimization in different applications such as lithium ion batteries, supercapacitors, solar cells, and fuel cells.