  The charge accumulation properties of p-i-n perovskite solar cells were
investigated using three representative organic and inorganic hole transporting
layer (HTLs): a) Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)
(PEDOT:PSS, Al 4083), b) copper-doped nickel oxide (Cu:NiOx) and c) Copper
oxide (CuO). Through impedance spectroscopy analysis and modelling it is shown
that charge accumulation is decreased in the HTL/Perovskite interface, between
PEDOT:PSS to Cu:NiOx and CuO respectively. This was indicative from the
decrease in double layer capacitance (Cdl) and interfacial charge accumulation
capacitance (Cel), resulting in an increase to recombination resistance (Rrec),
thus decreased charge recombination events between the three HTLs. Through AFM
measurements it is also shown that the reduced recombination events (followed
by the increase in Rrec) is also a result of increased grain size between the
three HTLs, thus reduction in the grain boundaries area. These charge
accumulation properties of the three HTLs have resulted in an increase to the
power conversion efficiency between the PEDOT:PSS (8.44%), Cu:NiOx (11.45%) and
CuO (15.3%)-based devices.
