Improving the conductivity of sol–gel derived NiOx with a mixed oxide composite to realize over 80% fill factor in inverted planar perovskite solar cells.

Charge extraction efficiency is one of the key factors to determine the performance of solar cells, which depends on the electronic properties of the electron and hole transporting layers. Sol–gel derived NiO_x as the hole transporting layer (HTL) used in perovskite solar cells (PVSCs) promises both low-cost and high-stability. However, current NiO_x based PVSCs have a relatively low fill factor (FF) and device efficiency. Here, we show that using an oxide composite approach by incorporating thermally reduced graphene oxide (rGO) into the NiO_x layer (NiO_x:rGO) can effectively improve the film conductivity without sacrificing its high work function. The improved charge extraction efficiency reduces the interfacial recombination loss and increases the carrier lifetime in NiO_x:rGO based PVSCs, which are evidenced by transient photocurrent and transient photovoltage measurements. The NiO_x:rGO based PVSC achieves a promising PCE of 19.1% with a significantly improved FF from 73% to 81% compared to the device using solely NiO_x. Moreover, the NiO_x:rGO based PVSC shows a decent photo-stability tracked at the maximum-power-point and a long shelf-lifetime with negligible degradation in device performance after 70 days. It is believed that the oxide composite transporting layer would be a promising alternative to further develop highly efficient and stable PVSCs. [ABSTRACT FROM AUTHOR]