Ricerc@Sapienza

The effect of sodium doping in NiO as a contact layer for perovskite solar cells
is investigated. A combined X-ray diffraction and X-ray photoelectron spectroscopy
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, the NiO/perovskite interface
in perovskite solar cells is modified via insertion of an ultrathin NaCl interlayer,

In perovskite solar cells (PSCs), the interfaces are a weak link with respect to degradation. Electrochemical reactivity of the perovskite’s halides has been reported for both molecular and polymeric hole selective layers (HSLs), and
here it is shown that also NiO brings about this decomposition mechanism. Employing NiO as an HSL in p–i–n PSCs with power conversion efficiency (PCE) of 16.8%, noncapacitive hysteresis is found in the dark, which is