Recent Development of Lead-Free Perovskite Solar Cells

*Anshebo Getachew Alemu and Teketel Alemu*

### **Abstract**

Recently, the world energy demand has been raised up dramatically. Numerous energy sources have been developed to satisfy the urgent energy desires and to overcome the world energy crisis. Among them, solar energy has been considered an efficient energy source for current energy requirements. Nowadays, the lead-based perovskite solar cells achieved excellent power conversion efficiency exceeding 29.1%. However, to address major problems such as toxicity and underprivileged stability, several hardworks were made toward the replacement of lead-free perovskite material in perspective of device's performance and stability. In this book chapter, we summarize material, dimensions, stability, and the current achievement of lead-free solar cells. Finally, we review the remaining challenges and future perspective for development of lead-free perovskite solar cells.

**Keywords:** material, dimensions, stability, lead-free photovoltaics

### **1. Introduction**

Nowadays, among renewable energy alternatives, solar energy is the most abundant and has minimum impact on the environment compared with nonrenewable sources such as natural gas, fossil fuels, and nuclear energy. The development of photovoltaic has made possible the change of sunlight into electrical energy with high power conversion efficiencies with low cost [1, 2]. The demand of energy from the photon energy is primary significance because it is clean, renewable, abundant, and natural [3, 4]. Among the innovative photovoltaic, perovskite solar cells have hastily enhanced to the frontline for electricity production [5]. Solar-cells-based tandem perovskite achieved world high efficiency of 29.15% in the photovoltaic research field [6] and low production cost [7–9]. However, the increased concern of lead toxicity for extensive use in addition to the distress of disposal, widespread research effort has been dedicated to the path of lead-free PSCs [10, 11]. Due to encounters such as instability in ambient conditions [12], lack of accuracy in thickness [13], and device-incompatible solution growth processes [14, 15], PSCs have not yet gained sufficient trust for commercial applications.

Therefore, novel groups of lead-free halide PSCs have been discovered for substituting lead (Pb) with other elements such as antimony (Sb) [16], bismuth (Bi) [17], germanium (Ge), [18, 19], indium (In) [20, 21], tin (Sn), [22, 23], and double halide perovskite (**Figure 1**) possession the inherent perovskite properties

**Figure 1.**

*Structure of (a) Pb-perovskite (b) tin-halide perovskites (c) double-halide perovskites. X is a halide; M and M*<sup>0</sup> *stand for monovalent and trivalent metals, respectively [24, 25].*

**Figure 2.**

*Solar cell absorbers materials .A-site cations (organic MA and FA or inorganic Cs and Rb), metals, and halides (I, Br, Cl) for perovskite structure. b/ band gaps of different materials solar cells should have band gaps from 1.1 to 2.0 eV [26–31].*

unchanged. Furthermore, these alternative Pb-free materials show significant advantages such as highlight absorption coefficients, higher charge carrier mobilities, and narrow optical band gap compared with lead-based perovskites as shown in **Figure 2** [32].

This book chapter contains of the following sections: (1) introduction of metal halide PSCs, (2) origin of lead-free perovskite solar cells, (3) lead-free Pb-free

materials, (4) dimensions of Pb-free materials, (5) limitations of Pb-lead materials, and (6) future prospective have also been discussed.
