“…Each layer is very important, but, in practice, the loss of efficiency is closely related to the ability of the ETL to transport photogenerated electrons. The electron transport layer plays an important role within the structure of the solar cell, since the electron transport layer, depending on its morphology, the type of material from which it is built, and its physical properties, will be used for better stability, prolonged life, and offer higher PCE, some of the most widely used materials are metal oxides, some of the most commonly used materials are metal oxides, such as TiO 2 [ 8 , 9 , 10 ], ZnO [ 11 , 12 , 13 ], SnO 2 [ 14 , 15 , 16 ], SiO 2 [ 17 ], and ZrO 2 [ 18 , 19 ]; each material provides specific advantages.…”