Reconfiguration of Interfacial and Bulk Energy Band Structure for High-Performance Organic and Thermal–Stability Enhanced Perovskite Solar Cells

Tin oxide (SnO₂) offers its advantages in widespread applications that require efficient carrier transport. However, the usages of SnO₂ in organic solar cells are hindered because of dangling bonds on the surface of SnO₂. Herein, PFN-Br as an interfacial layer to tailor the work function of SnO₂ is adopted, making it an ideal candidate for interfacial material in organic electronics. Meanwhile, such an efficient SnO₂/PFN-Br electron transport layer (ETL) can also be applied to perovskite devices and achieve competitive efficiency. To eliminate current–voltage hysteresis and improve poor thermodynamic stability of perovskite solar cells (PSCs), 5 mol% of guanidinium iodide (GAI) into the (MA)_x(FA)_{1 − x}PbI₃ precursor solution is incorporated, enabling the formation of triple-cation perovskite films with excellent optoelectronic quality and stability. The combination of an SnO₂/PFN-Br ETL and GAI doping strategy finally delivers power conversion efficiencies over 21% and negligible current–voltage hysteresis in planar PSCs. These improvements arise from the strong hydrogen bonding caused by the incorporation of GA⁺. It can stiffen the inorganic Pb–I lattice of the unit cell and restrain the formation of iodine vacancies defects. Moreover, the strong hydrogen bonding can immobilize iodide ion and thus enhance the thermal stability of the corresponding device.