In two-step vacuum evaporation process, transporting layerprecursor are deposited in vacuum chamber A. Then substrates are transferred to chamber B to carry out the reaction. By controlled pressure in chamber B, we adjust the reaction rate. After reaction, smooth perovskite thin-film is formed. Finally, the substrates are transferred to chamber A to deposit the transporting layermetal.

A two-stage vacuum evaporation process breakthrough of the solution-process is found. Because of using the vacuum evaporation process, this technology is solvent-free. For vacuum evaporation, it is simple to make large scalesmooth perovskite thin-film. Moreover, vacuum evaporation process is also feasible to fabricate perovskite solar cells on the flexible substrates.

Currently, optoelectronic industry use vacuum evaporated machines to fabricate optoelectronic products. Therefore, vacuum evaporation process is simple to integrate with optoelectronic industry. Two-step vacuum evaporation process could be integrated to flexible substrate. Owing to excellent performance under indoor light intensity, it could be a power supplier for Internet of Things.