The effect of hole transporting layer in charge accumulation properties of p-i-n perovskite solar cells

The charge accumulation properties of p-i-n perovskite solar cells were investi- gated using three representative organic and inorganic hole transporting layer (HTL): (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 accumula- tion is decreased in the HTL/perovskite interface, between PEDOT:PSS to Cu:NiOx and CuO. This was indicative from the decrease in double layer capacitance (Cdl) and interfacial charge accumulation capacitance (Cel), resulting in an increase to recom- bination resistance (Rrec), thus decreased charge recombination events between the three HTLs. Through AFM measurements, it is also shown that the reduced recom- bination events (followed by the increase in Rrec) are also a result of increased grain size between the three HTLs, thus reduction in the grain boundary 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