Thermal evaporated PbI₂ enables high-quality perovskite films and improves their solar cell performance

The quality of the light-absorbing perovskite layer is essential for fabricating highly efficient and stable perovskite solar cells (PSCs). The utilization of vacuum-deposited PbI2, instead of spin-coated PbI2, significantly enhanced the quality of the perovskite film in a two-step deposition process. A uniform and agglomeration-free formation of the PbI2 layer achieved through the vacuum-deposition method promoted the efficient intercalation of MAI and led to the formation of a high-quality MAPbI(3) perovskite layer with enhanced optical properties and surface morphology. Through electrochemical impedance spectroscopy, we discovered that PSCs with vacuum-deposited PbI2 demonstrate suppressed ion migration compared to devices with spin-coated PbI2. With the application of vacuum-deposited PbI2, the power conversion efficiency (PCE) of the device is superior to devices using spin-coated PbI2. Moreover, after a 40 h thermal stability test, the device with vacuum-deposited PbI2 maintained a PCE of over 50% of its initial efficiency, while the PSC with spin-coated PbI2 dropped to 10%.