Progress is reported in these areas: Plasmonic Light Trapping in Thin Film a-Si Solar Cells; Plasmonic Light Trapping in Thin InGaN Quantum Well Solar Cells; and Earth Abundant Cu2O and Zn3P2 Solar Cells.

The fundamental concept of the book is to explain how to make thin film solar cells from the abundant solar energy materials by low cost. The proper and optimized growth conditions are very essential while sandwiching thin films to make solar cell otherwise secondary phases play a role to undermine the working function of solar cells. The book illustrates growth and characterization of Cu2ZnSn(S1-xSex)4 thin film absorbers and their solar cells. The fabrication process of absorber layers by either vacuum or non-vacuum process is readily elaborated in the book, which helps for further development of cells. The characterization analyses such as XPS, XRD, SEM, AFM etc., lead to tailor the physical properties of the absorber layers to fit well for the solar cells. The role of secondary phases such as ZnS, Cu2-xS,SnS etc., which are determined by XPS, XRD or Raman, in the absorber layers is promptly discussed. The optical spectroscopy analysis, which finds band gap, optical constants of the films, is mentioned in the book. The electrical properties of the absorbers deal the influence of substrates, growth temperature, impurities, secondary phases etc. The low temperature I-V and C-V measurements of Cu2ZnSn(S1-xSex)4 thin film solar cells are clearly described. The solar cell parameters such as efficiency, fill factor, series resistance, parallel resistance provide handful information to understand the mechanism of physics of thin film solar cells in the book. The band structure, which supports to adjust interface states at the p-n junction of the solar cells is given. On the other hand the role of window layers with the solar cells is discussed. The simulation of theoretical efficiency of Cu2ZnSn(S1-xSex)4 thin film solar cells explains how much efficiency can be experimentally extracted from the cells. - One of the first books exploring how to conduct research on thin film solar cells, including reducing costs - Detailed instructions on conducting research

The search for cleaner, cheaper, smaller and more efficient energy technologies has to a large extent been motivated by the development of new materials. The aim of this collection of articles is therefore to focus on what materials-based solutions can offer and show how the rationale design and improvement of their physical and chemical properties can lead to energy-production alternatives that have the potential to compete with existing technologies. In terms of alternative means to generate electricity that utilize renewable energy sources, the most dramatic breakthroughs for both mobile (i.e., transportation) and stationary applications are taking place in the fields of solar and fuel cells. And from an energy-storage perspective, exciting developments can be seen emerging from the fields of rechargeable batteries and hydrogen storage.

This book reviews the current status of semiconductor materials for conversion of sunlight to electricity, and highlights advances in both basic science and manufacturing. Photovoltaic (PV) solar electric technology will be a significant contributor to world energy supplies when reliable, efficient PV power products are manufactured in large volumes at low cost. Expert chapters cover the full range of semiconductor materials for solar-to-electricity conversion, from crystalline silicon and amorphous silicon to cadmium telluride, copper indium gallium sulfide selenides, dye sensitized solar cells, organic solar cells, and environmentally friendly copper zinc tin sulfide selenides. The latest methods for synthesis and characterization of solar cell materials are described, together with techniques for measuring solar cell efficiency. Semiconductor Materials for Solar Photovoltaic Cells presents the current state of the art as well as key details about future strategies to increase the efficiency and reduce costs, with particular focus on how to reduce the gap between laboratory scale efficiency and commercial module efficiency. This book will aid materials scientists and engineers in identifying research priorities to fulfill energy needs, and will also enable researchers to understand novel semiconductor materials that are emerging in the solar market. This integrated approach also gives science and engineering students a sense of the excitement and relevance of materials science in the development of novel semiconductor materials. · Provides a comprehensive introduction to solar PV cell materials · Reviews current and future status of solar cells with respect to cost and efficiency · Covers the full range of solar cell materials, from silicon and thin films to dye sensitized and organic solar cells · Offers an in-depth account of the semiconductor material strategies and directions for further research · Features detailed tables on the world leaders in efficiency demonstrations · Edited by scientists with experience in both research and industry

Thin film solar cells are promising to realize cheap solar energy. Compared to conventional wafer cells, they can reduce the use of semiconductor material by 90%. The efficiency of thin film solar cells, however, is limited due to insufficient light absorption. Sufficient light absorption at the bandgap of semiconductor requires a light path more than 10x the thickness of the semiconductor. Advanced designs for light trapping are necessary for solar cells to absorb sufficient light within a limited volume of semiconductor. The goal is to convert the incident light into a trapped mode in the semiconductor layer. In this dissertation, a critical review of currently used methods for light trapping in solar cells is presented. The disadvantage of each design is pointed out including insufficient enhancement, undesired optical loss and undesired loss in carrier transport. The focus of the dissertation is light trapping by plasmonic and photonic structures in thin film Si solar cells. The performance of light trapping by plasmonic structures is dependent on the efficiency of photon radiation from plasmonic structures. The theory of antenna radiation is used to study the radiation by plasmonic structures. In order to achieve efficient photon radiation at a plasmonic resonance, a proper distribution of surface charges is necessary. The planar fishnet structure is proposed as a substitution for plasmonic particles. Large particles are required in order to resonate at the bandgap of semiconductor material. Hence, the resulting overall thickness of solar cells with large particles is large. Instead, the resonance of fishnet structure can be tuned without affecting the overall cell thickness. Numerical simulation shows that the enhancement of light absorption in the active layer is over 10x compared to the same cell without fishnet. Photons radiated from the resonating fishnet structure travel in multiple directions within the semiconductor layer. There is enhanced field localization due to interference. The short circuit current was enhanced by 13.29%. Photonic structures such as nanodomes and gratings are studied. Compared to existing designs, photonic structures studied in this dissertation exhibited further improvements in light absorption and carrier transport. The nanodome geometry was combined with conductive charge collectors in order to perform simultaneous enhancement in optics and carrier transport. Despite the increased volume of semiconductor material, the collection length for carriers is less than the diffusion length for minority carriers. The nanodome geometry can be used in the back end and the front end of solar cells. A blazed grating structure made of transparent conductive oxide serves as the back passivation layer while enhancing light absorption. The surface area of the absorber is increased by only 15%, indicating a limited increase in surface recombination. The resulting short circuit current is enhanced by over 20%. The designs presented in the dissertation have demonstrated enhancement in Si thin film solar cells. The enhancement is achieved without hurting carrier transport in solar cells. As a result, the enhancement in light absorption can efficiently convert to the enhancement in cell efficiency. The fabrication of the proposed designs in this dissertation involves expensive process such as electron beam lithography. Future work is focused on optical designs that are feasible for cheap fabrication process. The designs studied in this dissertation can serve as prototype designs for future work.

Nanostructured solar cells are very important in renewable energy sector as well as in environmental aspects, because it is environment friendly. The nano-grating structures (such as triangular or conical shaped) have a gradual change in refractive index which acts as a multilayer antireflective coating that is leading to reduced light reflection losses over broadband ranges of wavelength and angle of incidence. There are different types of losses in solar cells that always reduce the conversion efficiency, but the light reflection loss is the most important factor that decreases the conversion efficiency of solar cells significantly. The antireflective coating is an optical coating which is applied to the surface of lenses or any optical devices to reduce the light reflection losses. This coating assists for the light trapping capturing capacity or improves the efficiency of optical devices, such as lenses or solar cells. Hence, the multilayer antireflective coatings can reduce the light reflection losses and increases the conversion efficiency of nanostructured solar cells.

The two tasks performed by a solar cell are absorption of sunlight and collection of the photogenerated charges. In a conventional planar solar cell, these two processes are coupled because charges produced by light that is absorbed deep within the semiconductor must travel a long distance to the junction near the surface before they can be separated and collected. Core-shell nanowire arrays decouple the directions of light absorption and charge separation, allowing the collection of charges from poorly absorbing materials with relatively short minority carrier diffusion lengths. Additionally, because the dimensions of nanowires are on the same length scale as the wavelength of visible light, light-trapping effects allow a film of nanowires to absorb more light than would a thin film made from the equivalent volume of material. In the development of nanowire array solar cells, single-nanowire solar cells provide information about the optical and electronic properties of the junction in a particular material system. They are a simplified experimental platform that can be used to screen materials for their suitability for nanowire array solar cells. This work describes the opto-electronic properties of single-wire solar cells made from silicon, CdS/Cu2S, and ZnO/Cu2O. While silicon is a model system used to investigate fundamental optical effects, the oxide and sulfide heterojunctions are attractive for photovoltaics because of their low cost and elemental abundance in the earth's crust; they are also particularly well suited for nanowire array, rather than planar, solar cells because of their sub-micrometer minority carrier diffusion lengths. Suspended, silicon single-nanowire solar cells served as a model system with which to develop characterization techniques such as scanning photocurrent mapping (SPCM) and wavelength-dependent photocurrent measurements and to understand the optical properties of single-nanowire solar cells. These measurements and electromagnetic simulations of the wire's absorption show that the devices exhibit enhanced photocurrent at the wavelengths corresponding to the optical resonances of the nanowire. After characterization of the devices, they were used to study the interaction between a nanoscale dielectric cavity, the silicon nanowire, and a plasmonic nanocrystal, which is summarized below. In planar solar cells, the CdS/Cu2S heterojunction is formed by a low-temperature cation-exchange reaction that creates an epitaxial interface between the two sulfides. This chemistry was adapted to single-nanowire solar cells and determined to produce high-quality junctions at the nanoscale, suitable for nanowire photovoltaics. The high carrier concentration of Cu2S or one of its neighboring Cu(2-x)S phases, however, often led to full depletion of the CdS nanowire core, prohibiting efficient collection of photogenerated charges. To address this difficulty, indium-doped CdS nanowires were synthesized, and single-nanowire solar cells were fabricated from them. I-V curves under simulated sunlight and SPCM show that the difficulty in collecting from the CdS core was resolved, and these devices yielded single-nanowire efficiencies averaging 2.5%. These indium-doped solar cells were also used as platforms to study the interaction between a single-nanowire solar cell and plasmonic nanocrystals, discussed below. Finally, the cation-exchange chemistry was applied to hydrothermally synthesized CdS nanorod arrays to produce micro-array nanorod solar cells with efficiencies reaching 0.2%. In recent photovoltaic research, nanomaterials have offered two new approaches for trapping light within solar cells to increase their absorption: nanostructuring the absorbing semiconductor and using metallic nanostructures to couple light into the absorbing layer. These two approaches are combined in the study of silicon and In-CdS/Cu(2-x)S single-nanowire solar cells decorated with silver nanocrystals. Wavelength-dependent photocurrent measurements and finite-difference time domain (FDTD) simulations show that increases in photocurrent arise at wavelengths corresponding to the nanocrystal's surface plasmon resonances, while decreases occur at wavelengths corresponding to optical resonances of the nanowire. SPCM experimentally confirms that changes in the device's photocurrent come from the silver nanocrystal. These results demonstrate that understanding the interactions between nanoscale absorbers and plasmonic nanostructures is essential to optimizing the efficiency of nanostructured solar cells. Because of the earth-abundance, non-toxicity, and low cost of copper and zinc, the ZnO/Cu2O heterojunction is an attractive material system for solar energy conversion. Beginning with Cu2O wires synthesized via a high-temperature, vapor-phase reaction, single-wire ZnO/Cu2O and ZnO/TiO2/Cu2O heterostructure diodes were fabricated. Devices showed photocurrent and photovoltage under laser illumination, and a few exhibited photovoltaic performance under 1-sun illumination. The general lack of photoresponse under 1-sun conditions is attributed to full depletion of the Cu2O wire's core, greatly reducing its conductivity. For the devices that did function as solar cells under 1-sun conditions, a combination of the large size of the Cu2O wires, the charge-screening ability of the TiO2 buffer layer, and possible incorporation of chlorine into the wires is likely responsible for their improved performance.

Systematically describes the physical and materials properties of copper-based quaternary chalcogenide semiconductor materials, enabling their potential for photovoltaic device applications. Intended for scientists and engineers, in particular, in the fields of multinary semiconductor physics and a variety of photovoltaic and optoelectronic devices.

This book explores the incorporation of plasmonic nanostructures into organic solar cells, which offers an attractive light trapping and absorption approach to enhance power conversion efficiencies. The authors review the latest advances in the field and discuss the characterization of these hybrid devices using a combination of optical and electrical probes. Transient optical spectroscopies such as transient absorption and transient photoluminescence spectroscopy offer powerful tools for observing charge carrier dynamics in plasmonic organic solar cells. In conjunction with device electrical characterizations, they provide unambiguous proof of the effect of the plasmonic nanostructures on the solar cells’ performance. However, there have been a number of controversies over the effects of such integration – where both enhanced and decreased performance have been reported. Importantly, the new insights into the photophysics and charge dynamics of plasmonic organic solar cells that these spectroscopy methods yield could be used to resolve these controversies and provide clear guidelines for device design and fabrication.

This book is a printed edition of the Special Issue "Nanostructured Solar Cells" that was published in Nanomaterials