Menzel, D.; Al-Ashouri, A.; Tejada, A.; Levine, I.; Guerra, J.A.; Rech, B.; Albrecht, S.; Korte, L.: Field Effect Passivation in Perovskite Solar Cells by a LiF Interlayer. Advanced Energy Materials 12 (2022), p. 2201109/1-10
10.1002/aenm.202201109
Open Access Version
Abstract:
The fullerene C60 is commonly applied as the electron transport layer in highefficiency metal halide perovskite solar cells and has been found to limit their open circuit voltage. Through ultra-sensitive near-UV photoelectron spectroscopy in constant final state mode (CFSYS), with an unusually high probing depth of 5–10 nm, the perovskite/C60 interface energetics and defect formation is investigated. It is demonstrated how to consistently determine the energy level alignment by CFSYS and avoid misinterpretations by accounting for the measurement-induced surface photovoltage in photoactive layer stacks. The energetic offset between the perovskite valence band maximum and the C60 HOMO-edge is directly determined to be 0.55 eV. Furthermore, the voltage enhancement upon the incorporation of a LiF interlayer at the interface can be attributed to originate from a mild dipole effect and probably the presence of fixed charges, both reducing the hole concentration in the vicinity of the perovskite/C60 interface. This yields a field effect passivation, which overcompensates the observed enhanced defect density in the first monolayers of C60.