Preface

The use of energy can be traced back to humans (species of the genus *Homo*) starting about two million years ago when they started cooking their food using firewood. Cooking had a profound evolutionary effect because it increased food efficiency, which allowed humans to spend less time foraging, chewing, and digesting. Modern anthropologists argue that *Homo erectus* developed a smaller, more efficient digestive tract, which freed up body energy to enable larger brain growth. Extended arguments reveal that cooking and control of fire generally affected species development by providing warmth and helping to fend off predators, which helped human ancestors adapt to a ground-based lifestyle. As humans developed new skills with increased activities, energy interaction and usage emerged. Energy was used not only for domestic functions but also for space applications. With industrialization, humans realized that energy was needed to move machines and do other things as well. In this quest, and without understanding the consequences of using fossil fuels extensively, many problems arose. Researchers in energy embarked on a journey to try to solve some of the problems by studying different forms of renewable energy. To understand different needs, researchers have tried to come up with ways in which small-scale energy harvesting can be adapted to different needs that do not require heavy-duty energy production. Technological advancements point directly to this quest where some gadgets have been miniaturized and others developed to help humans live better lives.

This book attempts to present a number of ideas regarding a few selected smallscale energy harvesting methods and techniques as well as theories and products that may be helpful in improving the quality of life.

Chapter 1 outlines the potential of perovskite solar cells (PSCs) as a promising form of new solar cell for power generation due to their simple processing, abundance of materials, and architectural integration, as well as good power conversion efficiencies, which rocketed from 3.8% in 2009 to 23.3% in 2018. It is pointed out in the chapter that the toxic lead (Pb) element containing the chemical composition of typically used organic–inorganic halide perovskites hinders the practical applications of PSCs. The chapter, however, gives a general discussion on perovskite crystal structure along with serious efforts focused on Pb replacement in these devices. Elaborate fundamental features of tin (Sn)-based perovskites together with their performance in PSCs is then presented, and alternative elements, such as copper (Cu), germanium (Ge), bismuth (Bi), and antimony (Sb), are outlined. Last but not least in the chapter is a summary of the challenges and opportunities based on the chapter.

In Chapter 2, thermoelectric energy generation of electrical power from temperature gradients or differences in naturally occurring geothermal heat and rocks, or from waste heat in man-made equipment and industrial processes, are discussed. Their commercial applications to replace or recharge batteries in low-power electronic systems are presented. The fundamental thermoelectric theory related to power generation, including the theoretical analysis and numerical calculations required to calculate the thermoelectric efficiency and electrical power generated when a single thermoelectric couple is given as an example. The short-term challenge for thermoelectric energy harvesting, which is a cost-effective and practical solution to replace batteries, and can be scaled to provide sufficient power to operate electrical rotating machines such as low-power motors and pumps, is clearly outlined. On the other hand, the long-term challenge of improving the efficiency, power output, cost of thermoelectric modules, and energy harvesting systems, and to develop them from low-power to medium-power applications, is presented.

The work in Chapter 3 focuses on the development of new kinds of energy harvesters that could be used in various applications, including industrial, aerospace, or consumer markets. The main aspect explores transformation of different sources of energy, such as temperature, vibration, shock, etc., into usable electric power, which in normal conditions is wasted. The process of energy harvesting relies on harvesters employing magnetomechanical effects.

Chapter 4 introduces a new energy technology in small-scale energy harvesting in relation to triboelectric nanogenerators (TENGs) that can harvest ambient mechanical energy and convert it to electricity for continuously powering small electronic devices. The fundamental working mechanism and modes of a TENG are presented. The chapter outlines how the technology can harvest all kinds of mechanical energy, especially at low frequencies, such as human motion, walking, vibration, mechanical triggering, rotating tires, wind, moving automobiles, flowing water, rain drops, as well as ocean waves.

Chapter 5 deals with the exploitation of radio waves existing in the ambient environment for battery charging, called radiofrequency energy harvesting. A method based on spectrum sensing to allow wireless devices to select the frequency band with maximum power that exceeds a predefined threshold to charge the device is described. The power threshold can be determined according to battery type and its required charging power, and the device can use this power for battery charging.

Chapter 6 does not seem to fall directly under the subject matter of this book, but covers one of the promising directions in the use of solar energy—heliomaterials science, whether for large-scale or small-scale energy production. It was, therefore, thought necessary to include this chapter in the book. The work describes important characteristics of engineering processes such as capacity, maximum and average energy densities, uniformity of energy density distribution, focal spot size, characteristics of energy density distribution and its change in time, duration of the process, and start and stop mode rate, which must be taken into consideration when developing solar furnaces. The work also looks at the drawbacks of solar concentrators and the variability of the characteristics of the focal spot with time. New ideas on the implementation of such a system are given in the discussion and conclusion.

**Reccab Manyala**

**1**

**Chapter 1**

**Abstract**

**1. Introduction**

(A = CH3NH3

, Cl<sup>−</sup> , Br<sup>−</sup>

X = I<sup>−</sup>

+

Based Solar Cells

*Yingfeng Li, Bing Jiang and Meicheng Li*

lenges and opportunities based on the chapter contents.

devices which would benefit mankind in future endeavor.

+

(MA), CH(NH2)2

**Keywords:** toxicity, stability, lead-free perovskites, chemical composition

Organic-inorganic trihalide perovskite is generally represented by ABX3

octahedron (BX6) unit. It has been witnessed that structure distortions determine the physical/electrical properties of ABX3 perovskite [20]. For example, Goldschmidt's tolerance prediction can be used for the dimensional evaluation of a perovskite as follows:

> *t =* \_\_\_\_\_\_\_ (*rA + rX*) √

\_\_\_\_\_\_\_ **2**( *rB* + *rX*

(FA), Cs+

PSCs with organometal (Pb) halide perovskites as photo-absorber showed rapid development in terms of PCEs from 3.8 to 23.3% [1–7]. The typically used Pb-based perovskites possess several appealing advantages such as broadband absorption range, long diffusion length, low exciton binding energy, and high-charge-carrier mobility [2, 3, 8–14]. However, intrinsic toxicity of Pb-based perovskites is a serious issue for both human and environment [15–19]. In this context, the replacement of Pb element in PSCs is extremely important for economical clean energy conversion

). **Figure 1** illustrates the typical cubic perovskite structure with basic

; B = Cu2+, Pb2+, Sn2+, Ge2+, Bi3+, Sb3+;

(1)

Quest for Lead-Free Perovskite-

*Sajid Sajid, Jun Ji, Haoran Jiang, Xin Liu, Mingjun Duan,* 

*Dong Wei, Peng Cui, Hao Huang, Shangyi Dou, Lihua Chu,* 

Today, the perovskite solar cells (PSCs) are showing excellent potentials in terms of simple processing, abundance of materials, and architectural integration, as well as very promising device's power conversion efficiencies (PCEs), rocketed from 3.8% in 2009 to 23.3% in 2018. However, the toxic lead (Pb) element containing the chemical composition of typically used organic-inorganic halide perovskites hinders the practical applications of PSCs. This chapter starts with a general discussion on the perovskite crystal structure along with the serious efforts focused on Pb replacement in these devices. Section 2 will elaborate the fundamental features of tin (Sn)-based perovskites together with their performance in the PSCs. Other alternative elements, such as copper (Cu), germanium (Ge), bismuth (Bi), and antimony (Sb), will be discussed in Section 3. The end will summarize the chal-

The University of Zambia, School of Natural Sciences, Department of Physics, Lusaka, Zambia
