Nanomaterials for Innovative Energy Systems and Devices

Nanomaterials have shown unique optical, magnetic, electrical and other properties that are entirely different from their bulk counterparts. These emergent properties have shown potential applications in electronics, medicine and other fields. One of the most important applications utilizing the optical and electrical properties of nanomaterials is in solar cells. Solar energy has the potential to beat out global energy consumption demands, and therefore solar photovoltaic technology is one of the most promising renewable energy sources. At present, silicon solar cells are widely used photovoltaic technology because of high efficiency and stability. Moreover, the high fabrication cost and unsafe decomposition (after use) of silicon solar cells are the critical issues. These problems lead to search for some better alternatives. In this series, perovskite solar cells/PSCs have appeared as promising cost-effective alternatives to existing technologies. Herein, an exclusive study on role of nanomaterials as charge transport layers, absorber layers and electrodes in the fabrication of PSCs has been presented. Furthermore, role of nanomaterials as buffer layer in the fabrication of (perovskite) solar cells has been discussed which could enhance the morphology of deposited layers, and hence increase the overall performance of these solar cells.

The present chapter is devoted to the synthesis, properties, and applications of graphitic carbon nitrides in perovskite solar cells (PSCs). Graphitic carbon nitride (g-C₃N₄) is an organic semiconducting polymeric material that is analogous in structure to the two-dimensional sp²-hybridized graphene sheets. It is a metal-free polymer with a tunable bandgap of 1.8–2.7 eV. This makes it possible to absorb light in the visible spectrum of 460–698 nm thus converting 13 to 49% of solar energy to useful electrical energy. In PSCs, g-C₃N₄ acts as a photocatalyst embedded in the light-absorbing layer of the solar cell. Hence, g-C₃N₄ helps in improving the efficiency of PSCs by assisting in the charge absorption and generation at the light-absorbing layer. Due to their high photoabsorption and photoresponsiveness, semiconducting properties, high stability under physiological conditions, and good biocompatibility, graphitic carbon nitrides have won tremendous attention among researchers recently. Incorporation of g-C₃N₄ in perovskite absorber layers improves its crystallinity and passivates defects leading to reduced charge carrier recombination which ultimately results in higher power conversion efficiency of PSCs.

The global energy crisis is the most significant concern of the twenty-first century due to excessive consumption of non-renewable sources such as coal, natural gas, crude oil, etc. Renewable energy sources come out to be the most effective tool to solve these global issues. In this context, there is a need for the advancement of efficient energy storage systems for the complete utilization of renewable energy sources. To fulfill the requirement of continuous energy supply, advanced energy storage devices such as batteries and supercapacitors need to be developed. Various novel materials including metal nitrides, polyoxometalates (POMs) metal-organic frameworks (MOFs), and transition metal dichalcogenides (TMDs) have been used for the supercapacitor application. TMDs and their nanocomposites play a prominent role as active electrode materials in supercapacitors owing to their large surface area and variable oxidation states. TMDs serve as promising materials to achieve significantly high energy densities. Nowadays, supercapacitors are primarily used as a complementary aid to batteries due to their weakness in terms of low energy density. This chapter introduces the need for renewable energy and the importance of supercapacitors as an energy storage device in comparison to batteries. This also describes the supercapacitors and types of supercapacitors. Furthermore, the chapter presents the highlight and reviews the various synthesis methods of TMDs and their nanocomposites with their applications in supercapacitors for use in various fields including hybrid electric vehicles and wearable electronics. Recent advancements along with future challenges and prospects in the field of TMDs-based supercapacitors are also discussed.

Thermoelectric power generators (TEGs) are solid-state energy harvesters that have demonstrated their ability to transform the energy from thermal to electrical form via the Seebeck effect. However, this model of electric generation technology is limited to niche applications, viz., TEG in planetary explorations and the automobile industry. TEG provides one of the unsoiled forms of energy. In recent years, we have seen incredible advancements in TEGs with the use of thermoelectric alloys for power generation in different temperature regimes. The major strategies involved for better performed thermoelectric materials are (i) power factor enhancement through band structure engineering and (ii) reduction in thermal conductivity. These strategies either solo or in combination exhibit high zT thermoelectric materials. However, the development of TEG devices is still not up to the mark. The management of maximum heat transfer through the device is also interesting which needs to be dealt with for developing high-efficiency devices. The mechanism of heat conversion into electricity sounds simple but consists of inherent challenges. The desired value of the device figure of merit (ZT) can only be achieved with a synchronous optimization of electrical and thermal transport properties—electrical conductivity (σ) and Seebeck coefficient (S)—and thermal conductivity (κ). Along with ZT, the performance of TE devices also depends upon their making cost and usability in extreme conditions.

Among binary chalcogenides family, Bi₂Se₃ thin films have been attracted a lot due to their unique electrical and optical properties, which enables the development of thermoelectric, optoelectronics, and topological insulator-based devices and applications. In energy field, thermoelectric material thin films have many advantages in refrigeration and power generation such as environment-friendly solid-state devices without moving parts, scalable, lightweight, long, and reliable working life at low cost. In addition, Bi₂Se₃ is a very good three-dimensional topological insulator material in which the boundary states are topologically protected against defects and non-magnetic impurities. In this chapter, we report on the deposition of Bi₂Se₃ thin films on Si (111), sapphire (0001), quartz, and Si (100) (n- and p-types) substrates by r.f. magnetron sputtering system and their optical, electrical, and thermoelectric properties. The high-resolution X-ray diffraction characterization revealed the growth of c-axis oriented Bi₂Se₃ crystalline thin film after post-selenization process of sputtered thin films. Scanning electron microscopy and energy dispersive X-ray analysis disclosed truncated hexagonal/triangular large grains with nearly stoichiometry Bi₂Se₃ film on Si(111) and sapphire (0001) substrates. Raman spectroscopy analysis also supports the good structural quality of Bi₂Se₃ thin films on these substrates as main pronounced characteristic peaks in the low wavenumber region; namely, E²_g (in-plane) A¹_1g, and A²_1g (out-of-plane) modes were observed, which revealed the pure hexagonal phase of Bi₂Se₃. Further, optical, thermoelectric and electrical characterization of the Bi₂Se₃ thin films deposited under various conditions showed the importance of r.f. power and post-selenization processes on their properties. The nearly c-axis-oriented Bi₂Se₃ thin film using magnetron sputtering with good structural quality will pave the way for futuristic large-area thermoelectric and opto-electronics devices.

Zinc oxide (ZnO), an attractive functional material having fascinating properties like large band gap (~3.37 eV), large exciton binding energy (~60 meV), high transparency, high thermal, mechanical and chemical stability, easy tailoring of structural, optical and electrical properties, has drawn a lot of attention for its optoelectronic applications including energy harvesting. Some of the promising applications are solar cells, ultraviolet light emitting diodes, photodiodes, ultraviolet lasers, high-temperature electronics, and spintronics devices. ZnO is a very versatile material vindicating itself with different access such as nanostructures, epitaxial structures, composite, and thin films. The ZnO nanostructures exist in various shapes and sizes including 0-D (nanoparticles), 1-D (nanowires, nanorods), 2-D (nanopetals, sheets), and 3-D (nanoflowers, tetrapods) structures with its tunable band gap energy, nature malleable behavior, and its potential application in optoelectronic devices. The ZnO being naturally an n-type inorganic semiconductor has been used in various types of solar cells such as conventional Si wafer solar cells, thin film solar cells, organic solar cells (OPVs), dye-sensitized solar cells (DSSCs), perovskite solar cells, hybrid solar cells (HSCs), and in several organic/inorganic as well as inorganic/inorganic heterojunction solar cell concepts. The ZnO acts as electron transport material, thereby it plays a major role in all the emerging third-generation PV devices. The ZnO thin films have manifold properties to make it interesting in photovoltaic applications. The ZnO thin film, owing to its easy synthesis and simple deposition techniques, reliability, cost effectiveness, non-toxicity, high stability, and good optoelectronic properties, has been studied extensively in several PV devices including the conventional silicon wafer-based solar cells as an antireflection and surface passivation layer. Here, a short review on ZnO nanostructures and thin films is presented in the perspective of their photovoltaic applications in different roles which include, as capping layer, electron selective layer, window layer, buffer layer, antireflection and passivation layer, as well as active layer for different types of solar cells. A brief overview of the synthesis methods of ZnO nanostructures and different deposition techniques of ZnO thin films via physical methods, cost-effective chemical routes and green methods is discussed. A brief discussion on the structural, optical, and electrical properties of the ZnO nanostructures and thin films is also included which are important for their PV applications. Finally, the chapter briefly outlines the different types of solar cells’ structures employing ZnO (nanostructures and thin films) in different roles, progress so far, their state-of-art-performance, and the challenges associated with different ZnO-based photovoltaic devices are critically discussed. At last, chapter closes with a summary including a remark indicating the future prospects of ZnO-based PV devices.

Due to recent advancement in renewable energy productions, there is a huge demand of advanced energy storage system. To develop the efficient and high-density storage system there is a lot of focus on the applications of nanomaterials in energy storage systems. The batteries are the most important and widely used storage system among the different energy storage systems. A lot of research work is focused on improved performance of rechargeable batteries by studying the main component of the batteries which includes separators, electrolytes, and electrodes. In this chapter, the advances and role of electrode materials for the improved performance of the batteries and application of nanomaterials for attaining better capacity and long cycle life of rechargeable batteries have been discussed.

The research aimed at extraction and utilization of leachate oils obtained from food landfills and further combine them with nanoparticles in order to evaluate their performance and emission characteristics in engines. The landfill oil is originally extracted by a two-step transesterification process and its integration with nanoparticles (aluminium oxide and copper oxide) will be performed for the first time in this study. Hydrobromic acid was added in order to reduce the FFA content of the oil. FAME obtained by employing chemicals Hydrobromic acid and alkali KOH was close to 95.74% inspected by a GC machine. Stability of blends was enhanced by employing an ultrasonic reactor for agitation process. The BTE, BSFC and BP improved and all major exhaust emissions reduced. Among the nanoparticles, Al₂O₃ displayed better performance. Therefore, landfill oils if properly combined in right proportion with nanoparticles can be suitably employed as potential alternative to Petro-diesel fuel.

Energy can play an important role for industrial as well as technological advancement. Solar energy is one of the most useful sources of renewable energy. It is converted to electricity with the help of a technology called photovoltaic. Sun is said to be the source of renewable energy because the earth continuously receives solar energy through the sun. Solar technology can be classified into two parts; one is active solar system based upon an external instrument for harnessing energy and another is passive solar system which does not depend on external instruments. Semiconducting materials are the heart of electronics and optoelectronic devices and are helpful regarding devices due to their amplification properties, energy changing properties, etc. In present years, there has been considerable attention in the area of the II–VI group (CdSe, CdS, ZnSe, CdTe, etc.) semiconducting thin films because of their large range of applications. Among these, CdSe is one of the important semiconducting chalcogenide materials for its applications such as thin film transistors, solar cells, photovoltaic, optoelectronic devices, photoconductors, gas sensors, acousto-optical devices, etc. CdSe is not water-soluble, does not thermally decompose, is reliable optical as well as electrical properties such as direct energy band gap, high absorption coefficient on the visible range makes it a potential candidate for solar cell taken as an absorber layer. Several methods for thin film deposition have been adopted by various researchers like chemical vapour deposition, molecular beam epitaxy, spray pyrolysis, electrodeposition, chemical bath deposition, etc. CdSe is a direct band gap material, and at room temperature its energy band gap is equal to 1.72 eV which makes it a suitable candidate for solar cells, light-emitting diodes, photodetectors as well as other optoelectronic devices. CdSe is mainly opted for fabrication of these devices due to its large photosensitive characteristics in comparison to other II–VI materials.

Battery technology is continuously improving to meet out the demands of energy storage systems. The performance of the battery plays an important role; hence drastic enhancement in its performance is needed. There is a lot of scope for the improvement in the performance of the batteries with applications of nano-structured materials, which offer extraordinary physiochemical properties. The proper selection and the functional development of electrolyte is one of the effective ways to enhance the performance of the battery. The function of electrolytes is to prevent any unwanted chemical reaction during the Faradaic reaction at the electrodes in rechargeable batteries. Thus, the design of superior electrolytes is contingent upon a number of variables, including the nature of electrolyte, stability window, temperature stability, inertness, abundance, non-hazardousness and economical. There are variety of electrolytes available such as organic, aqueous, non-aqueous, polymer, ionic liquid and hybrid electrolytes. The use of nanomaterials and other additives in the electrolyte enhance the performance of the battery. Along with the general concept, this chapter discusses the role of different electrolytes and nanomaterials as additives for improved performance of the batteries.

Energy storage is the process of capturing energy generated at one time and storing it for later usage in order to alleviate energy demand–supply mismatches. Energy storage entails transferring energy from difficult-to-store forms to more handy or cost-effective forms. The physicochemical characteristics of the materials used are strongly related to the performance of electrochemical energy storage and conversion devices. Due to their extra ordinary electrical and mechanical characteristics, nanomaterials with remarkable structures have piqued curiosity, and their surface features also play a key role in electrochemical activity. A polymeric membrane which is placed in between negative and positive electrodes of battery to not make a direct contact and prevents electrical short circuiting is known as separator. At the same time, it also transfers ions to complete the circuit during the electrochemical process. This chapter delineates about the separators and their different types in accordance with their use in different batteries and their physical and electro-chemical properties, performance, their fabrication and production techniques. This chapter also discusses the evolution of separators from early lead acid batteries to lithium ion, lithium Sulphur, lithium metal, sodium ion, zinc air, alkaline Zn/MnO₂ and iron air batteries. Role of nanomaterials in separators is also presented in this chapter.

In this chapter, the understanding of OPVs working mechanism and device structures (conventional and inverted) comprising of different types of layers is presented. Subsequently, we detailed the functioning of each layer, in the layer stack of OPVs, and the material characteristics for these layers are discussed. The active layer morphologies are detailed insight, along with their shortcomings and solution to improve them. The improvisation in optical absorption of the active layer by incorporation of plasmonic nanostructures in the different layers is also discussed. Furthermore, the use of nanotechnologies in each layer of the device is highlighted. The different types of loss-mechanism such as charge transfer loss, radiative and non-radiative recombinations are also been discussed in conjunction with the techniques to minimize these losses. Finally, the fabrication techniques, i.e., solution-processing and vacuum-processing, and roll-to-roll manufacturing of the OPVs are explained with their advantages and disadvantages. The chemical and physical degradation mechanisms leading to instabilities are also detailed insight. Along with this, the different encapsulation techniques to improve the stability of the device are elaborated.

Supercapacitors are important storage devices that display high specific capacitance much faster than batteries. They are emerging class of technology that offer higher density than traditional capacitors. This chapter is based on the review of Polyaniline (PANI)-based nanocomposite as supercapacitor electrode materials. PANI is one of the widely studied candidates for supercapacitors for one decade simply because of its eco-friendly nature, high electrical conductivity, inherently electrochemical property, extraordinary specific capacitance, and low cycling stability. The main limitation of PANI as a supercapacitor is its low cycle life. Because of this limitation, there are recent developments in PANI-based nanocomposites with carbon, activated carbon, carbon nanotubes, metal oxide, transition metal oxides, etc. This chapter will focus on achieving the high performance of the newly cultivated PANI‐based supercapacitors with and without binder addition into the PANI network. In addition, the chapter includes a brief fundamental concept of the standard synthesis and the analysis of the electrochemical properties of PANI with and without binder-based supercapacitors. Moreover, many new interesting advanced PANI composites/nanocomposites supercapacitors have also been included in this chapter.

The composite development has undergone a drastic change after the Second World War. Due to the remarkable physical and mechanical properties and high strength to weight ratio, the conventional metal-based components are bandied by the composites. The main constituents of composites are (1) matrix and (2) reinforcement. The matrix transfers stress, binds the reinforcement, and ultimately provides a unique shape to the composites. The common matrix used is metal, polymer, and ceramic. In these variants, polymer matrix composites (PMC) dominate the industrial field, especially in the aviation industry due to their excellent overall properties. The adversity in composite recycling is the separation of each structure from components. At the service of end-of-life, composites are either incinerated or deposited as landfills which induce serious environmental threats. The prolonged use of synthetic resins invokes depletion of fossil fuel, high environmental impact, and everlasting health issues in human beings and animals. To resolve this pressing dilemma the researchers focused on the development of an eco-friendly product named green composites. Green composites constitute a biodegradable polymer matrix and natural fiber-based fillers. In recent years the plant fibers like jute, hemp, coconut, and wood fibers replaced conventional fibers like glass, carbon, aramid, etc. Commonly used biodegradable polymer matrix composites are polylactic acid, polyhydroxy butyrate, starch, etc. The recent advancements in research is oriented on the development of green nanocomposites by the addition of nanoparticles. The nanoparticle addition will induce superior mechanical, thermomechanical properties, and thermal stability. By the adequate selection of polymer, the recycling process will reform the existing predicaments of polymer waste disposal. Extensive usage of biodegradable polymer will cause the recovery of repercussions due to synthetic polymer usage. Hence, green nanocomposites are playing a vital role in balancing the ecosystem and for sustainable development.