Dual-Site Passivation Coupling Internal Encapsulation via 3,5-Bis(trifluoromethyl)benzenethiol for Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) have made significant progress in efficiency, but their long-term operational stability remains an important yet challenging issue. Here, a dual-site passivation coupling internal encapsulation strategy is developed by introducing 3,5-bis(trifluoromethyl)-benzenethiol (35BBT) at the perovskite (PVK)/hole transport layer (HTL) interface. 35BBT provides dual active sites containing sulfur (S) atoms and fluorine (F) atoms, where the S atoms in the sulfhydryl group and the F atoms in the trifluoromethyl group coordinate with unpaired Pb²⁺ to form coordinate bonds, meanwhile the F atoms in the trifluoromethyl group form hydrogen bonds with organic cations. This dual-site passivation mitigates deep and shallow defects at the PVK/HTL interface. Notably, 35BBT, with hydrophobic trifluoromethyl and benzene rings covering the perovskite layer, enables internal encapsulation to protect the perovskite films from water and oxygen invasion. Consequently, the Ag-based device with 35BBT treatment achieves an efficiency enhancement from 22.03% to 23.86%, retaining 89.1% of its initial efficiency even after 2000 h of air exposure. This fabricated device also exhibits long-term thermal stability at 60 °C. This study offers an avenue for simultaneously passivating deep and shallow defects at the PVK/HTL interface and inhibiting water/oxygen erosion, thereby enabling the fabrication of efficient and stable PSCs for future commercial applications.