Low temperature, solution processed spinel NiCo2O4 nanoparticles as efficient hole transporting material for mesoscopic n-i-p perovskite solar cells

Spinel Nickel cobaltite oxide (NiCo2O4) have received great interest due to its usage in several industrial applications. The motivation of the present study is to explore the usefulness of spinel Nickel cobaltite oxide as inorganic charge transporting layer for standard perovskite solar cells (PSCs). This is the first demonstration of successful use of NiCo2O4 nanoparticles as hole transporting layer (HTL) in standard PSCs with the triple cation perovskite material. The synthesis of nanoparticles was done using a facile chemical precipitation method without the use of surfactant. The synthesized nanoparticles were characterized by the various techniques like X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), Field emission scanning electron microscopy (FESEM), and UV-vis spectroscopy (UV-vis). The co-ordination of Ni in Co3O4 matrix, as well as M+n-O bond lengths, were confirmed by the XAS studies. The standard mesoporous PSCs were fabricated by spin-coating a thin layer of NiCo2O4 (120 nm), and fabricated PSCs show an esteemed power conversion efficiency (PCE) of > 14% (under standard illumination conditions) and long-term stability (under ambient condition RH = 30-40%) as compared to the spiro-based PSCs. To improve the device performance further we also fabricated the PSCs using the interfacial hole transporting layer, presenting a PCE of > 16% with almost negligible hysteresis that is comparable to the normal standard PSCs based on spiro-OMeTAD as HTL. The performance of PSCs was further analysed by Electrochemical Impedance Spectroscopy (EIS), Photoluminescence (PL), Time-resolved Photoluminescence (TrPL) studies. The results showed the reduced recombination resistance in the PSCs using NiCo2O4 as well as interfacial layer. These outcomes indicate the effectiveness of NiCo2O4 interlayer for stable and highly efficient perovskite solar cells.