Perovskite solar cells (PSCs) with both normal (n-i-p) and inverted (p-i-n) mesoscopic structures usually exhibit higher efficiency than their planar counterparts because the mesoporous charge transport layers can supply heterogeneous nucleation sites for growing high quality perovskite crystals and enlarged charge separation area for better charge extraction. However, comparing with the achieved extremely high or even the certified world record efficiency of mesoscopic PSCs, the significant improvement of inverted mesoscopic PSCs has yet been made, mainly owing to the lack of suitable p-type semiconductors for preparing mesoporous hole transport layers (HTLs). Here, an emulsion-based bottom-up self-assembly strategy is used to prepare NiO microspheres from well-dispersed NiO nanocrystals. The self-assembled NiO microspheres are further used to fabricate mesoporous NiO HTLs of the inverted mesoscopic PSCs. The as-prepared mesoporous NiO HTL with self-assembled NiO microspheres can provide more suitable graded energy alignment, better charge carrier dynamics and reduced dark recombination in the device comparing with the inverted planar PSC with NiO nanocrystal HTL, contributing to obviously enhanced photovoltaic performance and nearly eliminated photocurrent-voltage hysteresis. Due to the general strategy of emulsion-based bottom-up self-assembly for microspheres synthesis, it will overcome the shortage of p-type materials for preparing efficient inverted mesoscopic PSCs.