Photoenergy and Thin Film Materials

Xiao-Yu Yang

• Publisher: Wiley-Scrivener
• Year: 2019
• Print ISBN: 9781119580461
• eBook ISBN: 9781119580478
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Energy

This book provides the latest research & developments and future trends in photoenergy and thin film materials—two important areas that have the potential to spearhead the future of the industry.

Photoenergy materials are expected to be a next generation class of materials to provide secure, safe, sustainable and affordable energy. Photoenergy devices are known to convert the sunlight into electricity. These types of devices are simple in design with a major advantage as they are stand-alone systems able to provide megawatts of power. They have been applied as a power source for solar home systems, remote buildings, water pumping, megawatt scale power plants, satellites, communications, and space vehicles. With such a list of enormous applications, the demand for photoenergy devices is growing every year.

On the other hand, thin films coating, which can be defined as the barriers of surface science, the fields of materials science and applied physics are progressing as a unified discipline of scientific industry. A thin film can be termed as a very fine, or thin layer of material coated on a particular surface, that can be in the range of a nanometer in thickness to several micrometers in size. Thin films are applied in numerous areas ranging from protection purposes to electronic semiconductor devices.

The 16 chapters in this volume, all written by subject matter experts, demonstrate the claim that both photoenergy and thin film materials have the potential to be the future of industry.

Part I
ADVANCED PHOTOENERGY MATERIALS

Chapter 1
Use of Carbon Nanostructures in Hybrid Photovoltaic Devices

Teresa Gatti^* and Enzo Menna^*

Department of Chemical Sciences, University of Padova, Padova, Italy

^*Corresponding authors: [email protected]; [email protected]

Abstract

This chapter provides an overview of the advantages resulting from the inclusion of carbon nanostructures (CNSs) within the different components of last-generation hybrid photovoltaic (HPV) devices. Among hybrid devices, here only dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are considered. In particular, the latter have been attracting the attention of researchers for less than a decade, but are extremely promising. In this context, CNSs are employed as auxiliary materials, to boost performances and stabilities, as well as to make production costs even lower. This chapter is indeed focused on carbon nanotubes, graphene-based materials and fullerenes. After briefly recalling the configuration of DSSCs and PSCs and the structures and properties of CNSs, strategies of CNS integration within different components of devices are described. Special attention is drawn to chemical functionalization of CNSs, enabling easier processing and addressing selective interactions with other species. Then, the discussion directs towards the roles played by the different CNS species in HPV cells, highlighting in particular strategies for improving device stability. Indeed the topic recalls nowadays a large attention from the scientific community. Finally, perspectives are indicated for further improvements of performances through the inclusion of CNSs in HPV devices.

Keywords: Carbon nanostructures, hybrid photovoltaics, carbon nanotubes, graphene based materials, fullerenes, dye sensitized solar cells, perovskite solar cells

1.1 Introduction

The need for stable photovoltaic (PV) devices comes along with the search for new solutions able to lower the overall costs of production of solar panels. PV devices based on single-crystal silicon are nowadays available on the market, providing power conversion efficiencies (PCEs) as high as 23% and 25 years operational lifetimes, as generally guaranteed by manufacturers [1]. Nevertheless, big efforts are addressed at developing new processes for their production ensuring higher-throughput, lower costs and better robustness.

Innovative perspectives were opened with the rise of organic PV (OPV) [2], which came into the international research focus at the beginning of the new millennium with the novel donor-acceptor bulk heterojunction (BHJ) architecture [3], and can provide today up to 13% PCE and encouraging lifetimes of more than 5000 hr for un-encapsulated devices [4]. At the same time, the combination of organic and inorganic materials allowed the development of alternative PV structures, defined from now on as hybrid PV (HPV) [5]. OPV and HPV are both part of the so-called “third generation” of solar devices.

Within HPV, we can distinguish two promising solutions, which couple good PCE with significant opportunities to develop low-cost, industry-scalable technologies, namely dye sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). The latter are somehow a direct legacy of the former and indeed their development is mostly based on the previous knowledge built up after more than two decades of intensive research. DSSCs [6] are also named “Graetzel-type” solar cells, after the inventor, Michael Graetzel, from the École Polytechnique Fédérale de Lausanne [7]. These devices feature a light-harvesting architecture based on a photosensitizer material, able to split excitons into separated charges, and a metal oxide semiconductor acting as the electron acceptor. In DSSCs, the photosensitizer is a molecular dye, often consisting of a ruthenium polypyridine complex, although this class is nowadays put aside by the development of metal-free organic dyes, allowing the elimination of expensive heavy metal components [6]. The advent of perovskite absorbers in 2009 [8], starting from hybrid methylammonium lead halides, evolving to hybrid mixed cation lead halides [9] and finally to all-inorganic perovskites [10], has significantly shifted the attention of the research community from DSSCs to PSCs. Perovskite materials are indeed characterized by outstanding light-absorption properties, high charge-carrier mobility and lifetime. This allows to produce solar cells with PCEs overcoming those of classical DSSCs by almost a 50% factor, with a current certified record of 23.3% (registered in 2018) [11].

The evolution of device architectures from classical DSSCs to solid state DSSCs (ssDSSCs) and then to mesoporous and planar PSCs is well described in Figure 1.1, taken from a short perspective on the rise of perovskites authored by Snaith in 2013 [12]. The replacement of the liquid electrolyte, employed in standard DSSCs, with solid hole conductors such as the well-known spiro-compound 2,20,7,70-tetrakis-(N,N-di-p-methoxyphenylamine)9,90-spirobifluorene (Spiro-OMeTAD) or the p-type semiconducting polymer poly(3-hexylthiophene) (P3HT) has allowed to overcome stability drawbacks related to undesired leakages of liquids and corrosion phenomena. At the same time, PCEs have suffered from a certain overall decrease when going from liquid-electrolyte DSSCs to ssDSSCs. The use of a mesoporous metal oxide architecture as the scaffold for the deposition of the perovskite absorbers leads to the meso-superstructured PSCs, in which hole extraction is operated, as in ssDSSC, by a solid hole transporting material (HTM), since a liquid electrolyte would dissolve the perovskite salt. The perovskite layer is either very thin (as reported in Figure 1.1) or extends further out of the mesoporous scaffold generating a perovskite-based “capping layer” on which the HTM is deposited (not depicted in the figure). Good PCEs are obtained also by employing PSCs based on planar architectures, where the active perovskite layer has a thickness around 0.5 µm. This happens since perovskites are able to generate and transport both electrons and holes to the collecting contacts with close to unity efficiency [12].

Figure 1.1 Historical evolution of light harvesting architectures, going from standard DSSCs based on liquid electrolytes (left) to ssDSS...

Table of contents

• Cover
• Title page
• Copyright page
• Preface
• Part I: Advanced Photoenergy Materials
• Part II: Advanced Thin Films Materials
• Index
• End User License Agreement