Superwetting Nanofluids of NiO x -Nanocrystals/CsBr Solution for Fabricating Quality NiO x -CsPbBr 3 Gradient Hybrid Film in Carbon-Based Perovskite Solar Cells.

The wettability of precursor solution on substrates is the critical factor for fabricating quality film. In this work, superwetting nanofluids (NFs) of non-stoichiometric nickel oxide (NiO x ) nanocrystals (NCs)-CsBr solution are first utilized to fabricate quality NiO x -CsPbBr 3 hybrid film with gradient-distributed NiO x NCs in the upper part for constructing hole transport ladder in carbon-based perovskite solar cells (C-PSCs). As anticipated, the crystalline properties (improved crystalline grain diameters and reduced impurity phase) and hole extraction/transport of the NiO x -CsPbBr 3 hybrid film are improved after incorporating NiO x NCs into CsPbBr 3 . This originates from the superb wettability of NiO x -CsBr NFs on substrates and the excellent hole-transport properties of NiO x . Consequently, the C-PSCs with the structure of FTO/SnO 2 /NiO x -CsPbBr 3 /C displays a power conversion efficiency of 10.07%, resulting in a 23.6% improvement as compared with the pristine CsPbBr 3 cell. This work opens up a promising strategy to improve the absorber layer in PSCs by incorporating NCs into perovskite layers through the use of the superwettability of NFs and by composition gradient engineering.