Efficient NiOx Hole Transporting Layer Obtained by the Oxidation of Metal Nickel Film for Perovskite Solar Cells

In the preparation of PSCs, NiO x is considered to be one very promising hole transport layers for its intrinsic p-type doping nature, deep-lying valence band, and high light transmittance. However, the thickness, uniformity, and composition of the NiO x film are not easy to accurately control by the solution spin-coating process. In this work, instead of the solution-processed NiO x, metal Ni is first deposited on the FTO/glass substrate by an e-beam evaporator and then converted to the NiO x by exposing it in the air with the help of annealing, which avoids the usage of a toxic solvent in the solution method. The deposition thickness and composition of the NiO x films could be well controlled. The results demonstrate that the Ni-oxidized NiO x HTL shows wonderful energy alignment, better charge extraction capability, and great efficiency in photoluminescence quenching when in contact with the perovskite film. By combining the two-step solution process method, high-performance PSC has been achieved based on the Ni-oxidized NiO x HTL, which is well above that based on the PEDOT:PSS and the solution-processed NiO x . Also, transient photocurrent (TPC) and transient photovoltage (TPV) measurements demonstrate that the device based on the Ni-oxidized NiO x HTL possesses a suppressed charge recombination and an outstanding ability of charge extraction. Furthermore, the Ni-oxidized NiO x -based devices exhibit better stability compared to the devices based on solution-processed NiO x and PEDOT:PSS HTL. All the results show that the Ni oxidation method is an efficient method to prepare the NiO x HTL in PSCs.