**3. Materials**

The existence of Pb is an urgent problem in contradiction of the final application of PSCs and the toxicity of lead disturbs the operational of the blood kidneys, liver, testes, brain, and nervous system [55]. In order to address toxicity and poor stability lead (Pb)-based perovskite, several hard works were made toward the replacement of lead-free perovskite material. In this section, we give comprehensive review of the Pbsubstitutes, such as Ge-based perovskite, bismuth-based perovskite, Sn-based perovskite, alkaline-earth metals perovskite, transition-metal-based perosivikate, and heterovalent perovskite.
