Di Girolamo, D.; Phung, N.; Jost, M.; Al-Ashouri, A.; Chistiakova, G.; Li, J.; Márquez, J.A.; Unold, T.; Korte, L.; Albrecht, S.; Di Carlo, A.; Dini, D.; Abate, A.: From Bulk to Surface: Sodium Treatment Reduces Recombination at the Nickel Oxide/Perovskite Interface. Advanced Materials Interfaces 6 (2019), p. 1900789/1-11

The effect of sodium doping in NiO as a contact layer for perovskite solar cells is investigated. A combined XRD and XPS analysis reveals that Na+ mostly segregates as NaOx/NaCl species around NiO crystallites, with the effect of reducing interface capacitance as revealed by impedance spectroscopy. Inspired by this finding, we modify the NiO/perovskite interface in perovskite solar cells via insertion of an ultra-thin NaCl interlayer, which increases the NiO work-function by 0.3eV. This leads to an increase of power conversion efficiency, approaching 18%, and open-circuit voltage due to a remarkable suppression of surface recombination, as revealed by photoluminescence analysis and light intensity dependent electrical measurements.