Surface Modification of NiO Nanoparticles for Highly Stable Perovskite Solar Cells Based on All-Inorganic Charge Transfer Layers

In the conventional n-i-p structure of perovskite solar cell (PSC), spiro-OMeTAD is used as the hole transport layer. However, some additives in spiro-OMeTAD, such as LiTFSI and TBP, can bring risks for perovskite degradation. Nickel oxide (NiO), a wide-band gap (3.6–4.0 eV) p-type semiconductor material with excellent electrical and optical properties, is widely applied in the PSCs and other fields. Given the suitable valence and conduction bands, NiO can effectively block electrons and transport holes, which are generated in the perovskite film after illumination. However, depositing a compact and thin NiO layer on the perovskite film is difficult because of the heat and solvent sensitivity of organic–inorganic hybrid perovskite. Here, we propose a facile method to prepare well-dissolved NiO nanoparticles in chlorobenzene, and the NiO film on perovskite is further modified by oxygen plasma or hexanethiol treatment to enhance the hole conductivity. Finally, we obtain a n-i-p structured PSC on the basis of all-inorganic charge transport layer with an efficiency of 4.21% using the prepared NiO film, and the value is further improved to 6.10% after oxygen plasma post-treatment. Moreover, the working stability is enhanced remarkably as the spiro-OMeTAD is replaced by NiO film, which is important for the application of PSCs.